Multiple response optimization of processing and formulation parameters of Eudragit RL/RS-based matrix tablets for sustained delivery of diclofenac

CONTEXT

Multiple response optimization is an efficient technique to develop sustained release formulation while decreasing the number of experiments based on trial and error approach.

OBJECTIVE

Diclofenac matrix tablets were optimized to achieve a release profile conforming to USP monograph, matching Voltaren^®SR and withstand formulation variables. The percent of drug released at predetermined multiple time points were the response variables in the design. Statistical models were obtained with relative contour diagrams being overlaid to predict process and formulation parameters expected to produce the target release profile.

MATERIALS AND METHODS

Tablets were prepared by wet granulation using mixture of equivalent quantities of Eudragit RL/RS at overall polymer concentration of 10-30%w/w and compressed at 5-15KN.

RESULTS AND DISCUSSION

Drug release from the optimized formulation E4 (15%w/w, 15KN) was similar to Voltaren, conformed to USP monograph and found to be stable. Substituting lactose with mannitol, reversing the ratio between lactose and microcrystalline cellulose or increasing drug load showed no significant difference in drug release. Using dextromethorphan hydrobromide as a model soluble drug showed burst release due to higher solubility and formation of micro cavities.

CONCLUSION

A numerical optimization technique was employed to develop a stable consistent promising formulation for sustained delivery of diclofenac.

STUDYING THE IMPACT OF FORMULATION AND PROCESSING PARAMETERS ON THE RELEASE CHARACTERISTICS FROM HYDROXYPROPYL METHYLCELLULOSE MATRIX TABLETS OF DICLOFENAC

Hydrophilic matrices, especially HPMC based, are widely used to provide sustained delivery where drug release occurs mainly by diffusion. A 3(2) full factorial design was used to develop and evaluate HPMC matrix tablet for sustained delivery of diclofenac. The influences of polymer concentration/viscosity, diluent type/ratio, drug load/solubility, compression force and pH change on drug release were investigated. Ten tablet formulations were prepared using wet granulation. HPMC K15M (10-30% w/w) was used as the polymer forming matrix. The release kinetics, compatibility studies, lot reproducibility and effect on storage were discussed. Increasing polymer concentration and compression force showed antagonistic effect on release rate. Mannitol tends to increase release rate more than lactose. Reversing diluent ratio between lactose and MCC did not affect drug release. Changing pH resulted in burst release whereas drug solubility is pH independent. F1 showed similar release to Voltaren SR and followed Higuchi model. Drug and polymer were compatible to each other. The formulation is stable at long and intermediate conditions with a significant increase in release rate at accelerated conditions due to water uptake and polymer swelling. The developed formulation was successful for a sustained delivery of diclofenac.

Role of adenosine A2A receptor in cerebral ischemia reperfusion injury: Signaling to phosphorylated extracellular signal-regulated protein kinase (pERK1/2)

Following brain ischemia reperfusion (IR), the dramatic increase in adenosine activates A2AR to induce further neuronal damage. Noteworthy, A2A antagonists have proven efficacious in halting IR injury, however, the detailed downstream signaling remains elusive. To this end, the present study aimed to investigate the possible involvement of phospho-extracellular signal-regulated kinase (pERK1/2) pathway in mediating protection afforded by the central A2A blockade. Male Wistar rats (250-270 g) subjected to bilateral carotid occlusion for 45 min followed by a 24-h reperfusion period showed increased infarct size corroborating histopathological damage, memory impairment and motor incoordination as well as increased locomotor activity. Those events were mitigated by the unilateral intrahippocampal administration of the selective A2A antagonist SCH58261 via a decrease in pERK1/2 downstream from diacyl glycerol (DAG) signaling. Consequent to pERK1/2 inhibition, reduced hippocampal microglial activation, glial tumor necrosis factor-alpha (TNF-α) and brain-derived neurotropic factor (BDNF) expression, glutamate (Glu), inducible nitric oxide synthase (iNOS) and thiobarbituric acid reactive substances (TBARS) were evident in animals receiving SCH58261. Additionally, the anti-inflammatory cytokine interleukin-10 (IL-10) increased following nuclear factor (erythroid-derived 2)-like 2 (Nrf-2). Taken all together, these events suppressed apoptotic pathways via a reduction in cytochrome c (Cyt. c) as well as caspase-3 supporting a crucial role for pERK1/2 inhibition in consequent reduction of inflammatory and excitotoxic cascades as well as correction of the redox imbalance.

Splenda alters gut microflora and increases intestinal p-glycoprotein and cytochrome p-450 in male rats

Splenda is comprised of the high-potency artificial sweetener sucralose (1.1%) and the fillers maltodextrin and glucose. Splenda was administered by oral gavage at 100, 300, 500, or 1000 mg/kg to male Sprague-Dawley rats for 12-wk, during which fecal samples were collected weekly for bacterial analysis and measurement of fecal pH. After 12-wk, half of the animals from each treatment group were sacrificed to determine the intestinal expression of the membrane efflux transporter P-glycoprotein (P-gp) and the cytochrome P-450 (CYP) metabolism system by Western blot. The remaining animals were allowed to recover for an additional 12-wk, and further assessments of fecal microflora, fecal pH, and expression of P-gp and CYP were determined. At the end of the 12-wk treatment period, the numbers of total anaerobes, bifidobacteria, lactobacilli, Bacteroides, clostridia, and total aerobic bacteria were significantly decreased; however, there was no significant treatment effect on enterobacteria. Splenda also increased fecal pH and enhanced the expression of P-gp by 2.43-fold, CYP3A4 by 2.51-fold, and CYP2D1 by 3.49-fold. Following the 12-wk recovery period, only the total anaerobes and bifidobacteria remained significantly depressed, whereas pH values, P-gp, and CYP3A4 and CYP2D1 remained elevated. These changes occurred at Splenda dosages that contained sucralose at 1.1-11 mg/kg (the US FDA Acceptable Daily Intake for sucralose is 5 mg/kg). Evidence indicates that a 12-wk administration of Splenda exerted numerous adverse effects, including (1) reduction in beneficial fecal microflora, (2) increased fecal pH, and (3) enhanced expression levels of P-gp, CYP3A4, and CYP2D1, which are known to limit the bioavailability of orally administered drugs.

Imidacloprid induces neurobehavioral deficits and increases expression of glial fibrillary acidic protein in the motor cortex and hippocampus in offspring rats following in utero exposure

Imidacloprid, a neonicotinoid, is one of the fastest growing insecticides in use worldwide because of its selectivity for insects. The potential for neurotoxicity following in utero exposure to imidacloprid is not known. Timed pregnant Sprague-Dawley rats (300-350 g) on d 9 of gestation were treated with a single intraperitoneal injection (i.p.) of imidacloprid (337 mg/kg, 0.75 x LD50, in corn oil). Control rats were treated with corn oil. On postnatal day (PND) 30, all male and female offspring were evaluated for (a) acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity, (b) ligand binding for nicotinic acetylcholine receptors (nAChR) and muscarinic acetylcholine receptors (m2 mAChR), (c) sensorimotor performance (inclined plane, beam-walking, and forepaw grip), and (d) pathological alterations in the brain (using cresyl violet and glial fibrillary acidic protein [GFAP] immunostaining). The offspring of treated mothers exhibited significant sensorimotor impairments at PND 30 during behavioral assessments. These changes were associated with increased AChE activity in the midbrain, cortex and brainstem (125-145% increase) and in plasma (125% increase). Ligand binding densities for [3H]cytosine for alpha4beta2 type nAchR did not show any significant change, whereas [3H]AFDX 384, a ligand for m2mAChR, was significantly increased in the cortex of offspring (120-155% increase) of imidacloprid-treated mothers. Histopathological evaluation using cresyl violet staining did not show any alteration in surviving neurons in various brain regions. On the other hand, there was a rise in GFAP immunostaining in motor cortex layer III, CA1, CA3, and the dentate gyrus subfield of the hippocampus of offspring of imidacloprid-treated mothers. The results indicate that gestational exposure to a single large, nonlethal, dose of imidacloprid produces significant neurobehavioral deficits and an increased expression of GFAP in several brain regions of the offspring on PND 30, corresponding to a human early adolescent age. These changes may have long-term adverse health effects in the offspring.

Testicular germ-cell apoptosis in stressed rats following combined exposure to pyridostigmine bromide, N,N-diethyl m-toluamide (DEET), and permethrin

This study reports and characterizes the testicular apoptosis following daily exposure of male Sprague-Dawley rats to subchronic combined doses of pyridostigmine bromide (PB, 1.3 mg/kg/d in water, oral), a drug used for treatment of myasthenia gravis and prophylactic treatment against nerve agents during the Persian Gulf War; the insect repellent N,N-diethyl m-toluamide (DEET, 40 mg/kg/d in ethanol, dermal); and the insecticide permethrin (0.13 mg/kg in ethanol, dermal), with and without stress for 28 d. Combined exposure to these chemicals was implicated in the development of illnesses including genitourinary disorders among many veterans of the Persian Gulf War. Previous studies from this laboratory have shown that exposure to combination of these chemicals produced greater toxicity compared to single components. Exposure to stress alone did not cause any significant histopathological alterations in the testes. Administration of combination of these chemicals induced apoptosis in rat testicular germ cells, Sertoli cells, and Leydig cells, as well as in the endothelial lining of the blood vessels. Testicular damage was significantly augmented when the animals were further exposed to a combination of chemicals and stress. Histopathological examination of testicular tissue sections showed that apoptosis was confined to the basal germ cells and spermatocytes, indicating suppression of spermatogenesis. Increased apoptosis of testicular cells coincided, in timing and localization, with increased expression of the apoptosis-promoting proteins Bax and p53. Furthermore, significant increase of 3-nitrotyrosine immunostaining in the testis revealed oxidative and/or nitrosation induction of cell death. In conclusion, combined exposure to real-life doses of test compounds caused germ-cell apoptosis that was significantly enhanced by stress.

Pharmacokinetic profile and placental transfer of a single intravenous injection of [(14)C]chlorpyrifos in pregnant rats

The pharmacokinetics and placental transfer of a single intravenous dose of 5.0 mg/kg (10 micro Ci/kg) ring-labeled [(14)C]chlorpyrifos were investigated in pregnant Sprague-Dawley rats at 11-13 days of gestation. Three rats were killed at 5, 15 or 30 min, or 1, 2, 4, 8, 12, 18, 24, 36, 48, 72 or 96 h after dosing. Radioactivity and 3,5,6-trichloropyridinol (TCP) were detected in all tissues 5 min after dosing. Chlorpyrifos was only found in maternal plasma and liver. Peak maternal plasma concentration of radioactivity ( micro g chlorpyrifos equivalents/ml) was 157 at 5 min, compared with 1.9 for fetal plasma at 15 min. The maximum concentrations of radioactivity ( micro g chlorpyrifos equivalents/g), detected in most tissues within 12 h of dosing, were, in descending order: liver (30), brain (29), placenta (21), and fetus (2). All peaks occurred at 5 min except for fetus and fetal plasma, which were at 15 min. TCP was detected by HPLC as the major compound identified in plasma and tissues. The maximum concentration detected was in plasma, at 12.4 micro g/ml, and for the following tissues was: liver 4.3 ng/g fresh tissue, fetus 4 ng/g, placenta 2.97 ng/g, brain 1.68 ng/g, and fetal plasma 0.52 ng/g. All TCP peaks occurred at 5 min except for fetus at 30 min and fetal plasma at 15 min. Parent chlorpyrifos was detected in maternal plasma and liver at maximum concentrations of 5.1 micro g/ml and 0.40 micro g/g, respectively, at 5 min. Chlorpyrifos was detectable in maternal plasma up to 36 h after dosing, and in liver up to 24 h after dosing. Pharmacokinetic analysis best described radioactivity, chlorpyrifos, and TCP as disappearing biexponentially from plasma and tissues. The terminal elimination half-lives of radioactivity, chlorpyrifos and TCP from maternal plasma were 16, 18, and 16 h, respectively. The results indicate that (1). chlorpyrifos undergoes a rapid metabolism to its major metabolites (TCP); (2). chlorpyrifos and its metabolites are distributed to all maternal and fetal tissues and plasma; and (3). the elimination of chlorpyrifos and TCP is slow, with redistribution from lipid stores a likely determinant of elimination rates.

Early differential elevation and persistence of phosphorylated cAMP-response element binding protein (p-CREB) in the central nervous system of hens treated with diisopropyl phosphorofluoridate, an OPIDN-causing compound

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus-ester-induced delayed neurotoxicity in sensitive species. We studied the effect of single dose of DFP on the expression of phosphorylated cAMP-response element binding protein (p-CREB), which is a well known transcription factor involved in several pathways mediating different types of external stimuli. The hens were perfused with neutral buffered formalin at different time points, i.e., 0.5, 1.0, and 2.0 hrs, as well as 1, 2, 5, and 20 days after dosing. The central nervous system regions of the whole brain were dissected and 7-micron sections were stained for either p-CREB immunopositivity or with hematoxylin and eosin. Results indicated an early differential increase of p-CREB immunopositivity in susceptible regions such as cerebellum, brainstem, and midbrain within 2 hrs. These induced levels persisted upto 5 days in these tissues, although the time course of p-CREB immunopositivity was distinctly different for each region. In the cerebellum induction of p-CREB was seen in the granular layer where both the granulocytes and the glial cells showed induction. Increased immunopositivity for p-CREB in the Purkinje cells and in some basket cells of the molecular layer was noticed over time, but the induction was not as great as in the granular layer. Of all the tissues cerebellum showed the strongest intensity of immunopositivity of the cells as well as the highest (absolute) number of pCREB-positive cells. The brainstem showed a similar fluctuating pattern like the cerebellum with the highest percentage increase of the immunoreactive cells at 5 days preceded by the lowest dip in immunopositivity at 2 days. In the midbrain, there was a time-dependent increase in the immunopositivity from 0.5 hr onwards until reaching control levels at 20 days. Immunopositivity was also noted in portions of the spina medularis and spina oblongata. The cerebrum (non-susceptible tissue) of DFP-treated hens did not show much deviation from the controls. The endothelial cells of the susceptible regions showed induction at early time points, in contrast to the absence of induction in cerebrum. Spatial and temporal differences in the immunopositivity pattern indicate probable involvement of CREB-independent pathways also. Overall, the complex induction pattern of p-CREB, along with our earlier observations of the early induction of c-fos, c-jun and Protein Kinase A (PKA) as well as the induction of Calcium2+/Calmodulin dependent Protein Kinase II (CaM kinase II) at later periods, strongly suggest an activator role of CREB mediated pathways that may lead to the clinical development of delayed neurotoxicity.

Absorption, distribution, metabolism and excretion of daily oral doses of [14C]methyl parathion in hens

Adult hens were given oral daily doses of 2 mg (2 microC(i))/kg/day (14% of oral LD(50) in male rats) of [14C]methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate) for 10 consecutive days. Five treated hens were sacrificed at 1, 2, 4, 8, 12, 24, and 48 h after the last dose. Methyl parathion was absorbed from the gastrointestinal tract and distributed rapidly. Maximum radioactivity was detected in tissues within 8 h of dosing, (ng methyl parathion equivalent/g fresh tissue or ml plasma): Plasma (189.2), liver (94.7), kidney (146.2), brain (61.4), gastrointestinal tissues (106.7). Methyl parathion was detected in the plasma, kidney and liver, while methyl parathion metabolite p-nitrophenol was detected in the liver and in the kidney. Elimination of methyl parathion from plasma was monophasic with a terminal half-life of 17.5 h, corresponding to an elimination rate constant of 0.039 ng/hr. Most of the absorbed radioactivity was excreted in the combined fecal-urine excreta (98%). Analysis of the metabolites in the excreta revealed that non-conjugated metabolites accounted for 13% of the total excretion. Conjugated metabolites accounted for 87% of the total excretion; of that, 6% as p-nitrophenyl-glucoronide conjugate, 7% as p-nitrophenyl-sulfate conjugate, 23% as bound hot sulfuric acid hydrolyzable residues, and 51% as water soluble metabolites. The presence of majority of radioactivity in the excreta as conjugated metabolites indicates that determining only unbound p-nitrophenol as a biological marker for methyl parathion exposure underestimates total fecal-urine excretion of p-nitrophenol. The slow elimination rate of methyl parathion is significant, since hens are more comparable to humans with respect to their cytochrome P450 activities.

Synthesis of some 2-methylthiouracil nucleosides and its 5-halo analogues of 2-acetamido-2-deoxy-D-glucose

This paper describes the regiospecific synthesis of 5-halo-2-methylthiouracil nucleosides by direct glycosylation followed by halogenation by an electrophilic halogen reagent and sodium azide under mild conditions. The compounds were suggested to be effective as antiviral agents.

Evidence for the involvement of central I1 imidazoline receptor in ethanol counteraction of clonidine hypotension in spontaneously hypertensive rats

Our previous studies have shown that ethanol counteracts centrally mediated hypotensive responses to clonidine. In this study, we investigated the relative roles of central alpha2-adrenergic and I1 imidazoline receptors in the antagonistic ethanol-clonidine hemodynamic interaction. The effects of selective blockade of alpha2- or I1 receptor by 2-methoxyidazoxan and efaroxan, respectively, on the blood pressure and heart rate responses to clonidine and subsequent ethanol administration were evaluated in conscious spontaneously hypertensive rats. Intracisternal administration of clonidine (1.5 microg/kg) produced significant (30 mm Hg; p < 0.05) and sustained (at least 60 min) decreases in blood pressure and heart rate. Systemic ethanol (1 g/kg), administered 10 min after clonidine, counteracted the hypotensive response and restored blood pressure to the preclonidine levels. Treatment with 2-methoxyidazoxan (0.16 microg/kg, intracisternal) or efaroxan (0.45 microg/kg, intracisternal) produced similar attenuation of the hypotensive and bradycardic responses to clonidine. The ability of ethanol to counteract the hypotensive action of clonidine was significantly (p < 0.05) attenuated in rats pretreated with efaroxan. The pressor response to ethanol lasted only 10 min compared with at least 60 min in the absence of efaroxan. In contrast, ethanol counteraction of clonidine-evoked hypotension was not altered when alpha2-adrenoceptors were blocked by 2-methoxyidazoxan. These findings suggest that centrally mediated hypotensive and bradycardic effects of clonidine in conscious spontaneously hypertensive rats involve activation of both alpha2-adrenergic and I1 imidazoline receptors. Furthermore, the findings suggest the dependence of a fully expressed ethanol counteraction of the hypotensive action of clonidine on functional I1 receptor within the central nervous system.

An association between the estrogen-dependent hypotensive effect of ethanol and an elevated brainstem c-jun mRNA in female rats

We have recently demonstrated that chronic ethanol administration lowers blood pressure (BP) in female rats and this effect is significantly attenuated by ovariectomy. The present study investigated whether ethanol hypotension is estrogen dependent. Further, since estrogen regulates AP-1 activity, the study was extended to determine whether estrogen/c-jun interaction is involved in the estrogen-dependent hypotensive effect of ethanol. Changes in BP and heart rate (HR) were evaluated in radiotelemetered pair-fed sham-operated (SO), ovariectomized (OVX), and OVX estradiol (E2)-treated rats receiving liquid diet with or without ethanol (5%, w/v) for 12 weeks. The in situ hybridization technique was used to measure the c-jun mRNA expression in two brainstem areas, the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (RVLM). Ethanol feeding caused significant (P<0.05) decreases in BP in SO rats that started at week 1 and reached its maximum (approximately 10 mmHg) at week 6 and remained at that level till the end of week 12. In OVX rats, ethanol had no effect on BP during the first 5 weeks after which a decrease of 5 mmHg was demonstrated and remained thereafter. Estrogen replacement (17beta-estradiol subcutaneous pellet, 14.2 microg/day) restored the hypotensive effect of ethanol to a level similar to that of SO rats both in terms of magnitude and duration. Densitometric analysis of the in situ hybridization autoradiograms revealed that OVX and E2 replacement had no effect on c-jun mRNA expression in the NTS or RVLM. Ethanol feeding produced a significant (twofold) increase in c-jun mRNA expression in the RVLM of SO rats versus no effect in the NTS. The increased expression of c-jun mRNA observed following ethanol treatment in the RVLM of SO rats was abolished in OVX rats and restored to SO levels after E2 replacement. These findings suggest a link between the estrogen-dependent hypotensive effect of chronically administered ethanol and the increased expression of c-jun mRNA in the brainstem of female rats.

Effect of long-term ethanol feeding on brainstem alpha(2)-receptor binding in Wistar-Kyoto and spontaneously hypertensive rats

Our previous studies have shown that ethanol attenuates baroreflex function in Wistar-Kyoto (WKY) but not in spontaneously hypertensive rats (SHRs). The present study determined the effects of chronic ethanol administration on alpha(2)-binding sites in brainstem areas that modulate baroreflexes. In vitro autoradiography was utilized to evaluate the effect of a 3-month ethanol feeding on the density (B(max)) and affinity (K(D)) of alpha(2)-adrenoceptors in the middle (mNTS) and rostral (rNTS) portions of the nucleus tractus solitarius of SHRs and WKY rats. Autoradiographic examination of brainstem sections preincubated with [125I]p-iodoclonidine revealed no inter-strain differences in alpha(2)-binding in control rats. Ethanol feeding caused strain-dependent changes in alpha(2)-binding activity, which comprised significant (P<0.05) decreases in the density of alpha(2)-binding sites in both areas of the NTS in SHRs versus no effect in WKY rats. These findings do not favor a role for brainstem alpha(2)-adrenoceptors in ethanol-induced attenuation of baroreflexes. Interestingly, the ethanol-evoked reduction in the NTS alpha(2)-receptor density in SHRs may explain reported findings that ethanol abolishes the hypotensive effect of the alpha(2)-adrenoceptor agonist clonidine in this rat model.

Effects of daily dermal application of DEET and epermethrin, alone and in combination, on sensorimotor performance, blood-brain barrier, and blood-testis barrier in rats

DEET and permethrin were implicated in the development of illnesses in some veterans of the Persian Gulf War. This study was designed to investigate the effects of daily dermal application of these chemicals, alone or in combination, on the permeability of the blood-brain barrier (BBB) and blood-testes barrier (BTB) and on sensorimotor performance in male Sprague-Dawley rats. Groups of five rats were treated with a dermal daily dose of 4, 40, or 400 mg/kg DEET in ethanol or 0.013, 0.13, or 1.3 mg/kg permethrin in ethanol for 60 d. A group of 10 rats received a daily dermal dose of ethanol and served as controls. BBB permeability was assessed by injection of an iv dose of the quaternary ammonium compound [3H]hexamethonium iodide. While permethrin produced no effect on BBB permeability, DEET alone caused a decrease in BBB permeability in brainstem. A combination of DEET and permethrin significantly decreased the BBB permeability in the cortex. BTB permeability was decreased by treatment with DEET alone and in combination with permethrin. The same animals underwent a battery of functional behavior tests 30, 45, and 60 d after exposure to evaluate their sensorimotor abilities. All treatments caused a significant decline in sensorimotor performance in a dose- and time-dependent manner. These results show that daily dermal exposure to DEET, alone or in combination with permethrin, decreased BBB permeability in certain brain regions, and impaired sensorimotor performance.

Locomotor and sensorimotor performance deficit in rats following exposure to pyridostigmine bromide, DEET, and permethrin, alone and in combination

Since their return from Persian Gulf War (PGW), many veterans have complained of symptoms including muscle and joint pain, ataxia, chronic fatigue, headache, and difficulty with concentration. The causes of the symptoms remain unknown. Because these veterans were exposed to a combination of chemicals including pyridostigmine bromide (PB), DEET, and permethrin, we investigated the effects of these agents, alone and in combination, on the sensorimotor behavior and central cholinergic system of rats. Male Sprague-Dawley rats (200-250 gm) were treated with DEET (40 mg/kg, dermal) or permethrin (0.13 mg/kg, dermal), alone and in combination with PB (1.3 mg/kg, oral, last 15 days only), for 45 days. Sensorimotor ability was assessed by a battery of behavioral tests that included beam-walk score, beam-walk time, incline plane performance, and forepaw grip on days 30 and 45 following the treatment. On day 45 the animals were sacrificed, and plasma and CNS cholinesterase, and brain choline acetyl transferase, muscarinic and nicotinic acetylcholine receptors were evaluated. Animals treated with PB, alone or in combination with DEET and permethrin, showed a significant deficit in beam-walk score as well as beam-walk time as compared with controls. Treatment with either DEET or permethrin, alone or in combination with each other, did not have a significant effect on beam-walk score. All chemicals, alone or in combination, resulted in a significant impairment in incline plane testing on days 30 and 45 following treatment. Treatment with PB, DEET, or permethrin alone did not have any inhibitory effect on plasma or brain cholinesterase activities, except that PB alone caused moderate inhibition in midbrain acetylcholinesterase (AChE) activity. Treatment with permethrin alone caused significant increase in cortical and cerebellar AChE activity. A combination of DEET and permethrin or PB and DEET led to significant decrease in AChE activity in brainstem and midbrain and brainstem, respectively. A significant decrease in brainstem AChE activity was observed following combined exposure to PB and permethrin. Coexposure with PB, DEET, and permethrin resulted in significant inhibition in AChE in brainstem and midbrain. No effect was observed on choline acetyl transferase activity in brainstem or cortex, except combined exposure to PB, DEET, and permethrin caused a slight but significant increase in cortical choline acetyltransferase activity. Treatment with PB, DEET, and permethrin alone caused a significant increase in ligand binding for m2 muscarinic acetylcholine receptor (mAChR) in the cortex. Coexposure to PB, DEET, and permethrin did not have any effect over that of PB-induced increase in ligand binding. There was no significant change in ligand binding for nicotinic acetylcholine receptor (nAChR) associated with treatment with the chemical alone; a combination of PB and DEET or coexposure with PB, DEET, and permethrin caused a significant increase in nAChR ligand binding in the cortex. Thus, these results suggest that exposure to physiologically relevant doses of PB, DEET, and permethrin, alone or in combination, leads to neurobehavioral deficits and region-specific alterations in AChE and acetylcholine receptors.

Imidazoline I(1) receptor-induced activation of phosphatidylcholine-specific phospholipase C elicits mitogen-activated protein kinase phosphorylation in PC12 cells

In the present study, we tested the hypothesis that the activation of imidazoline I(1)-receptor, which is coupled to phosphatidylcholine-specific phospholipase C, results in downstream activation of mitogen-activated protein kinase (p42(mapk) and p44(mapk) isoforms) in PC12 cells. PC12 cells pretreated with nerve growth factor (50 ng/ml, 48 h) to initiate neuronal differentiation were incubated with [methyl-3H]choline and [3H]myristate. Activation of imidazoline I(1) receptor by rilmenidine (10 microM) caused time-dependent increases in diacylglycerol accumulation and phosphocholine release. The Western blotting analysis showed that rilmenidine (10 microM) produced a time-dependent activation of p42(mapk) and p44(mapk) that reached its maximum at 15 min and returned to control levels after 30 min. This finding was confirmed by immunofluorescence labeling of activated mitogen-activated protein kinase in the same model system. Efaroxan (imidazoline I(1)-receptor antagonist) or tricyclodecan-9-yl-xanthogenate (D609, phosphatidylcholine-specific phospholipase C inhibitor) attenuated the phosphorylation of p42(mapk) and p44(mapk) induced by rilmenidine. Nerve growth factor-induced phosphorylation of both mitogen-activated protein kinase isoforms was not affected by D609. These results support the hypothesis that the activation of the imidazoline I(1) receptor coupled phosphatidylcholine-specific phospholipase C results in the downstream activation of mitogen-activated protein kinase.

Subchronic effects following a single sarin exposure on blood-brain and blood-testes barrier permeability, acetylcholinesterase, and acetylcholine receptors in the central nervous system of rat: a dose-response study

Subchronic neurotoxic effects of sarin (O-isopropyl methylphosphonofluoridate) treatment at various doses in male Sprague Dawley rats were studied. The animals were treated with a single intramuscular (im) injection of 0.01, 0.1, 0.5, or 1 x LD50 (100 microg/kg). The animals were maintained for 90 d thereafter. [3H]Hexamethonium iodide was used to monitor the changes in blood-brain barrier (BBB) permeability in cortex, brainstem, midbrain, and cerebellum. Brainstem exhibited a significant decrease (approximately 58% of control) in uptake of [3H]hexamethonium iodide at 1 x LD50 dose. No significant changes were observed in BBB permeability in cortex, midbrain, and cerebellum at any dose. Plasma butyrylcholinesterase (BChE) activity remained unchanged, reflecting recovery of the enzyme activity from the initial inhibition following single exposure of 1 x LD50 sarin. Acetylcholinesterase (AChE) activity in the cortex remained inhibited (approximately 29%), whereas in the brainstem there was an increase (approximately 20%) at 1 x LD50 dose of sarin. The m2-selective muscarinic acetylcholine receptor (m2-mAChR) ligand binding was inhibited significantly at 1 x LD50 in the cortex, whereas brainstem showed significantly increased (approximately 45%) ligand binding at 1 x LD50 dose. Nicotinic acetylcholine receptor (nAChR), on the other hand, showed a biphasic response in ligand binding in the cortex with a decrease (approximately 30%) at 0.01 x LD50 but an increase (approximately 40%) at 1 x LD5O. Brainstem did not show any significant change in nAChR ligand binding. These results suggest that single exposure of sarin could lead to changes that may play an important role in neuropathological abnormalities in the central nervous system.

Effect of long-term ovariectomy and estrogen replacement on the expression of estrogen receptor gene in female rats

OBJECTIVE

Estrogen exerts a wide variety of actions involving many target tissues. We studied the effects of long-term ovariectomy (OVX) and OVX with 17beta-estradiol treatment (OVXE2) on the level of estrogen receptor (ER) gene expression in target tissues of female rats.

DESIGN

Three groups of Sprague-Dawley female rats were utilized in this study: sham operated (SO), OVX and OVXE2.

METHODS

SO and OVX were performed 2 weeks before starting the 17beta-estradiol treatment. All groups were maintained on liquid diet for 12 weeks from the time of estradiol treatment. Total RNA was prepared from the tissues of the rats and relative quantitative reverse transcription PCR was utilized to compare the ER alpha-subtype (ERalpha) mRNA level in the three groups for each target tissue.

RESULTS

Following long-term OVX, the levels of ERalpha expression showed a significant increase in the uterus, kidney and cerebral cortex and no significant change in the liver, cerebellum, brainstem, heart and thoracic and abdominal aorta compared with their SO levels. On the other hand, a 12-week treatment of OVX rats with 17beta-estradiol restored the previously upregulated ERalpha mRNA to near SO levels except for the liver where the 17beta-estradiol treatment resulted in a significant increase in the ERalpha mRNA level compared with that in SO rats.

CONCLUSIONS

We conclude that the regulation of ERs by its ligand is tissue specific.

Radiotelemetric evaluation of hemodynamic effects of long-term ethanol in spontaneously hypertensive and Wistar-Kyoto rats

This study determined the hemodynamic effects of chronic ethanol in telemetered freely moving age-matched spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Changes in blood pressure (BP), heart rate (HR), and plasma norepinephrine (as index of sympathetic activity) were evaluated in pair-fed rats receiving liquid diet with or without ethanol (5%, w/v) for 12 weeks. The SHRs exhibited higher baseline BP and lower HR compared with WKY rats. When normalized for body weight, daily ethanol intake was higher in SHRs compared with WKY rats. However, blood ethanol concentration was similar except for a higher level in SHRs at weeks 7 through 9. Ethanol had no effect on BP in WKY rats but caused decreases in BP in SHRs that reached a maximum (approximately 30 mm Hg) at week 5 and remained thereafter. Ethanol also caused reductions in the BP variability and the circadian fluctuations in BP in SHRs but not in WKY rats. Plasma norepinephrine levels were elevated by ethanol in WKY rats, but not in SHRs. The HR was not affected by ethanol in SHRs and showed increases in WKY rats. These findings suggest that chronic ethanol feeding differentially affects BP in SHRs (hypotension) and WKY rats (no effect). The lack of a hypotensive response to ethanol in WKY rats may relate, at least partly, to the associated sympathoexcitation. The present study used the telemetry technique for BP measurement, which eliminates the confounding and stressful effects of other conventional techniques.

Clonidine diminishes c-jun gene expression in the cardiovascular sensitive areas of the rat brainstem

The present study investigated the effect of clonidine on the basal and inducible c-jun and c-fos mRNA expression in the nucleus tractus solitarius (middle, mNTS, and rostral, rNTS) and the rostral ventrolateral medulla (caudal, cRVLM, and rostral, rRVLM). Conscious rats received saline, clonidine (30 microg/kg, i.v.), saline plus sodium nitroprusside (NP), or clonidine plus NP. Under basal conditions (saline-infused rats), c-jun mRNA was expressed in the mNTS and rRVLM but not in the rNTS or cRVLM whereas c-fos mRNA was not detectable. Clonidine attenuated the increases in c-fos in the mNTS and cRVLM and c-jun gene expression in the mNTS and rRVLM caused by NP-evoked hypotension and also reduced the basal expression of c-jun mRNA in the mNTS and rRVLM. These findings establish a causal link between clonidine inhibition of c-fos expression in brainstem and its hypotensive action, and provide the first evidence that clonidine attenuates the expression of the closely linked c-jun gene in neurons implicated in centrally mediated hypotension.

Neurotoxicity of ethyl methacrylate in rats

Ethyl methacrylate (ethyl 2-methyl-2-propenoate, EMA) has been implicated in the development of neurologic impairment following occupational exposure. The potential of EMA to produce neurotoxicity was investigated in adult male Sprague-Dawley rats in two experiments. In the first experiment, animals were administered 100, 200, 400, or 800 mg/kg by daily intraperitoneal (i.p.) injections for 60 d. Control rats received daily i.p. injections of 1 ml saline/kg. Clinical observations, spontaneous motor activity, and performance in the Morris water maze were assessed. Alterations in clinical parameters in the higher dose groups included lethargy, impaired breathing, decreased weight gain, and increased mortality. Alterations in motor activity were observed at 100 mg/kg, a dose that did not cause alterations in clinical parameters, body weight gain, or mortality. There was also a dose-dependent impairment in performance in the Morris water maze. In the second experiment, animals were administered EMA in drinking water at concentrations of 0.1, 0.2, or 0.5% for 60 d. Control rats were administered tap water. Animals were perfused at the termination of exposure and samples of brain, spinal cord, and sciatic nerve were prepared for histological examination. Spongiform alterations were observed in fiber tracts of the forebrain, brainstem, and spinal cord. Clusters of axonal swellings were scattered throughout the dorsal, ventral, and lateral columns of the spinal cord, and typically involved internodal segments of two or three neighboring axons. Shrunken axons with separated myelin lamellae and large axons with thinner than normal myelin sheaths were apparent in the sciatic nerve. The patterns of alterations in the white matter of the spinal cord and the sciatic nerve are consistent with myelinopathy, but additional experiments are necessary to confirm whether oligodendroglia and Schwann cells are the primary sites of injury. In addition to the alterations associated with myelin, there was a decrease in the density of neurons in the ventral horn of the spinal cord. While the observed effects of EMA on the nervous system of rats are consistent with neurologic symptoms of workers exposed to EMA, additional experiments are necessary to determine if the level and route of exposures associated with occupational use produce these impairments in experimental animals.

Placental transfer and pharmacokinetics of a single dermal dose of [14C]methyl parathion in rats

The pharmacokinetics and placental transfer of a single dermal 10.0 mg (10microCi)/kg dose of uniformly phenyl-labeled [14C] methyl parathion (0,0-dimethyl 0-4-nitrophenyl phosphorothioate) were investigated in pregnant Sprague-Dawley rats at 14-18 days of gestation. Three rats were killed at each time interval: 1, 2, 4, 12, 24, 48, 72, and 96 h after dosing. Radioactivity disappeared biexponentially from the administration sites, which retained 50% and 3% of the dose after 1 h and 96 h, respectively. Most of the absorbed radioactivity was excreted in the urine (91%). Only 3% of the 14C was recovered in the feces. One h after the administration, radioactivity was detected in all tissues, including fetal tissue. The peak maternal plasma concentration of radioactivity (ng methyl parathion equivalent/ml) was 1005 at 2 h, compared to 318 ng for fetal plasma at 12 h. The maximum concentrations of radioactivity (ng methyl parathion equivalent/g), detected in most tissues within 12 h of dosing, were, in descending order: adipose tissue (67,532), kidney (1,571), spleen (1,256), spinal cord (1,004), heart (729), liver (706), brain (546), placenta (389), and fetus (256). The metabolism studies showed that methyl parathion, detected by HPLC, was the major compound identified in plasma and tissues. The maximum concentration detected was in plasma, at 513 ng/ml, and in the following tissues (ng/g fresh tissue): kidney (819), fetus (668), placenta (394), liver (375), and brain (282). The metabolite methyl paraoxon was detected in maternal brain and liver at maximum concentrations (ng/g fresh tissue) of 135 and 64 after 12 h and 4 h respectively, while p-nitrophenol was only detected in liver at a maximum concentration of 21 ng/g 72 h after dosing. Pharmacokinetic studies showed that methyl parathion disappeared monoexponentially from plasma and tissues. The half-life of elimination of methyl parathion from plasma was 11 h corresponding to a constant rate value of 0.06 h(-1). The results indicate that skin and placenta are poor barriers against methyl parathion permeability, resulting in a rapid and extensive dermal absorption of this insecticide and extensive placental transfer. This is indicated by the relative residence (R(R)) of methyl parathion in the plasma, which was largest in the placenta followed by the fetus. This study suggests that pregnant women and fetuses may be at risk of cholinergic toxicity following dermal exposure to methyl parathion.

Ovariectomy alters the chronic hemodynamic and sympathetic effects of ethanol in radiotelemetered female rats

This study determined the chronic hemodynamic effects of ethanol in telemetered freely moving female Sprague-Dawley rats. The role of ovarian hormones and sympathetic activity in the modulation of ethanol responses was also investigated. Changes in blood pressure (BP), heart rate (HR), and plasma estrogen and norepinephrine (NE, as index of sympathetic activity) were evaluated in pair-fed sham-operated (SO) and ovariectomized (OVX) rats receiving liquid diet with or without ethanol (5%, w/v) for 12 weeks. OVX caused a significant increase (about 40 g) in body weight, compared with the sham operation, which was apparent after two weeks and remained so for the duration of the study. The body weight showed gradual and similar increases in both ethanol and control groups. Ethanol feeding had no effect on the plasma estrogen level in SO or OVX rats. Daily ethanol intake was significantly (P < 0.05) less in OVX compared with SO rats whereas the blood ethanol concentration were similar in the two groups except for a significantly (P < 0.05) higher level in OVX rats at weeks 8, 10, and 11. Ethanol feeding caused significant (P < 0.05) decreases in BP in SO rats that started at week land reached maximal response (approximately 10 mmHg) at week 6 and remained at that level till the end of week 12. In OVX rats, ethanol had no effect on BPduring the first 5 weeks of the study. A slight but significant reduction in BP (about 5 mmHg) by ethanol in OVX rats started to appear at week 6 and remained for the following 5 weeks. The reduced hypotensive effect of ethanol in OVX rats was associated with an increase in the sympathetic activity as indicated by the significant (P < 0.05) increases in plasma NE levels. This sympathoexcitatory effect of ethanol was not demonstrated in SO rats. The HR was not affected by ethanol in the two groups of rats except for significant (P < 0.05) increases at weeks 1 through 3 in SO rats. The present findings suggest that the ovarian hormones modulate, at least partly, the hemodynamic and neurohumoral effects of chronic ethanol feeding in female rats. Ethanol lowers BP in female rats and this effect was delayed and diminished in OVX rats due possibly to the associated increase in sympathetic activity.

Homoacyclovir analogues of unnatural bases and their activity against hepatitis B virus

The ambident nucleophilic nature of the sodium salts of 2(1H)-qunioxalinone (2) and the phthalazinedione (3) has been realized from their alkylation with 2-(2-chloroethoxy)ethylacetate (1) to afford 1-[2-(2-acetoxyethoxy)ethyl]-2(1H)-quinoxalinone (8) and 2-[2-(2-acetoxyethoxy)ethoxy]qunioxaline (9) as well as 10 and 11, respectively. The corresponding derivatives 12-15 were similarly prepared by the alkylation of the unnatural bases 4-7 with 1. Treatment of the alkylated derivatives 8-15 with methanolic ammonia solution (1:1) at room temperature gave the corresponding hydroxyalkyl derivatives 16-23. The site of the alkylation was deduced from the spectral characteristics of the products. The activity of compounds 16-22 against Hepatitis B virus (HBV) in HepG2 cell has been tested. Some of the compounds showed high viral replication inhibition with low cytotoxicity.

Sexually dimorphic hemodynamic effects of intragastric ethanol in conscious rats

This study investigated the gender-related differences in hemodynamic effects of small to moderate doses of intragastrically (i.g.) administered ethanol in conscious rats. Changes evoked by ethanol (0.25, 0.5 or 1 g/kg) in mean arterial pressure (MAP), heart rate, cardiac index (CI), stroke volume (SV), and total peripheral resistance (TPR) were followed for 90 min in age-matched male and female Sprague-Dawley rats. Baseline values of MAP (121+/-2 vs. 124+/-2 mm Hg) were similar whereas CI (55+/-2 vs. 43+/-2 ml/min/100 g) and TPR (2.2+/-0.1 vs. 3.0+/-0.1 mm Hg/ml/min/100 g) were significantly (P<0.05) higher and lower, respectively, in female compared with male rats. In male rats, the middle dose (0.5 g/kg) of ethanol caused a slight increase in MAP due to significant (P<0.05) increases in CO whereas the other two doses (0.25 and 1 g/kg) had no effect on MAP. In female rats, MAP was not affected by ethanol (0.25 and 0.5 g/kg) and showed a significant reduction by the higher dose (1 g/kg) that was associated with decreases in CO and SV while TPR did not change. The hypotensive effect of ethanol (1 g/kg) in female rats started after 50 min, was maximal (13+/-1.7 mm Hg) at 70 min and remained so for the remaining 20 min of the study. Blood ethanol concentrations were similar in male and female rats. These findings suggest that the hemodynamic responses to i.g. ethanol are gender-related and that ethanol-evoked hypotension in female rats appears to involve a reduction in cardiac output.

Role of the sympathetic control of vascular resistance in ethanol-clonidine hemodynamic interaction in SHRs

Our previous studies showed that ethanol selectively counteracts centrally mediated hypotensive responses. In this study, we investigated the role of sympathetic nerve activity, cardiac output (CO), and total peripheral resistance (TPR) in this antagonistic hemodynamic interaction between ethanol and clonidine. Changes in blood pressure (BP), heart rate (HR), CO, stroke volume (SV), and TPR elicited by intracisternal (i.c.) clonidine and subsequent ethanol or saline were evaluated in conscious freely moving spontaneously hypertensive rats (SHRs). Clonidine (0.5 microg, i.c.) evoked hypotension was due to a significant reduction in TPR (from 3.6+/-0.21 to 2.8+/-0.17 mm Hg/ml/min/100 g), which was associated with a significant (p < 0.05) reduction in plasma norepinephrine (NE, from 660+/-115 to 310+/-50 pg/ml), measured as index of sympathetic activity. Ethanol (1 g/kg, i.v.) counteracted the hypotensive effect of clonidine and produced significant (p < 0.05) increases in plasma NE and TPR. Further support for the hypothesis that ethanol selectively counteracts centrally mediated hypotension was sought by investigating the effect of ethanol on peripherally mediated hemodynamic responses to hydralazine. Hydralazine (0.4 mg/kg, i.v.) produced a hypotension similar in magnitude to that produced by clonidine, which was also due to a significant reduction in TPR. However, unlike the case with clonidine, reflex increases in HR, SV, and hence CO were evident. Ethanol given after hydralazine produced a short-lived pressor effect (<10 min vs. 60 min in case of clonidine) in spite of a sustained increase in TPR. The latter was offset by the simultaneous decreases in CO, SV, and HR. A 30% increase in plasma NE caused by hydralazine returned to baseline level after ethanol or saline. Blood ethanol concentrations were similar in all treatment groups. These findings suggest that ethanol selectively counteracts centrally evoked hypotensive responses by counteracting the sympathoinhibition-mediated decreases in TPR elicited by centrally administered clonidine in conscious SHRs.

Synthesis and anti-hepatitis B virus activity of some 2,3-dihydroxyprop-1-yl unnatural hetaryls

The sodium salts of some hetaryls of the quinoxalin-2-ones 2-4, phthalazine-1,4-dione 5, phthalazin-1-one 6, and pyridazin-6-ones 7 and 8 were alkylated with (+/-) 2,3-O-isopropylidene-1-O-(4-toluenesulfonyl)glycerol (1) to give the respective tetraseco-nucleosides 9-15. Their deisopropylidenation with 70% acetic acid in water gave the corresponding 2,3-dihydroxyprop-1-yl hetaryls 16-22. Compounds 16-22 showed varying inhibition activity against Hepatitis B virus (HBV) with low to moderate cytotoxicity, where 18 and 21 showed the highest replication inhibition and low cytotoxicity.

Gender difference in baroreflex-mediated bradycardia in young rats: role of cardiac sympathetic and parasympathetic components

In a previous clinical study we have demonstrated a significantly lower baroreflex-mediated bradycardic response in young women compared with men. The present study determined whether sexual dimorphism in baroreflex sensitivity in young rats also covers the reflex tachycardic response. The study was then extended to test the hypothesis that an attenuated cardiac cholinergic component of the baroreflex heart rate response in females may account for the gender difference. Baroreflex sensitivity (BRS) was expressed as the regression coefficient of the reciprocal relationship between evoked changes in blood pressure and heart rate. BRS measured in conscious rats with phenylephrine (BRS(PE)) and nitroprusside (BRS(NP)) represented the reflex bradycardic and tachycardic responses, respectively. Female rats exhibited significantly lower BRS(PE) compared with male rats (-1.53+/-0.1 vs. -2.36+/-0.13 beats x min(-1) x mmHg(-1); p < 0.05) but similar BRS(NP) (-2.60+/-0.20 vs. -2.29+/-0.17 beats x min(-1) x mmHg(-1)). Blockade of cardiac muscarinic receptors with atropine methyl bromide elicited greater attenuation of BRS(PE) in male than in female rats (72+/-4.6 vs. 53+/-6.7% inhibition; p < 0.01) and abolished the gender difference. In male rats cardiac muscarinic blockade attenuated BRS(PE) significantly more than did cardiac beta-adrenergic receptor blockade with propranolol (72+/-4.6 vs. 43+/-2.7; p < 0.01), which suggests greater dependence of BRS(PE) on the parasympathetic component. In females, muscarinic and beta-adrenergic blockade elicited similar attenuation of BRS(PE). The findings suggest that (i) BRS is differentially influenced by gender; female rats exhibit substantially lower BRS(PE) but similar BRS(NP) compared with age-matched male rats and (ii) the sexual dimorphism in BRS(PE) results, at least partly, from a smaller increase in vagal outflow to the heart in response to baroreceptor activation.

Estrogen enhancement of baroreflex sensitivity is centrally mediated

We have recently shown that estrogen enhances baroreceptor control of reflex bradycardia in conscious rats. The present study replicated this finding in pentobarbital sodium-anesthetized rats, and the study was extended to investigate whether this effect of estrogen is centrally or peripherally mediated. Hemodynamic responses to electrical stimulation of the central end of the aortic depressor or the vagal efferent nerve were evaluated in pentobarbital sodium-anesthetized sham-operated (SO), ovariectomized (OVX), and OVX estradiol-treated Sprague-Dawley rats. Phenylephrine (1-16 microgram/kg iv) elicited dose-dependent pressor and bradycardic responses. Regression analysis of the baroreflex curves, relating changes in mean arterial pressure and heart rate, revealed a significantly smaller baroreflex sensitivity in OVX compared with SO anesthetized rats (-0.54 +/- 0.05 and -0.91 +/- 0.12 beats. min-1. mmHg-1, respectively; P < 0.05). Treatment of OVX rats with 17beta-estradiol (E2, 50 microgram. kg-1. day-1 for 2 days subcutaneously) significantly enhanced baroreflex sensitivity to a level similar to that of SO rats (P < 0.05). The enhancing effect of E2 on the baroreflex-mediated bradycardia, observed in conscious and anesthetized rats, seems to be selective because the baroreflex-mediated tachycardic responses measured in a separate group of conscious rats were not altered by ovariectomy or E2 administration. Electrical stimulation of the aortic nerve elicited frequency-dependent depressor and bradycardic responses that were significantly smaller in OVX compared with SO values (P < 0.05). Treatment of OVX rats with E2 restored the hemodynamic responses to aortic stimulation to near SO levels. On the other hand, hemodynamic responses to vagal stimulation were not affected by OVX or treatment with E2. These findings suggest that enhancement of reflex bradycardia by estrogen is centrally mediated and involves interaction with central projections of the aortic nerve.

Estrogen-dependent hypotensive effects of ethanol in conscious female rats

This study investigated the role of estrogen in the acute hemodynamic responses to intragastric (i.g.) ethanol in conscious female rats. Changes evoked by ethanol or equal volume of water in mean arterial pressure, heart rate, cardiac index, stroke volume (SV), and total peripheral resistance were followed in sham-operated, ovariectomy (OVX) vehicle-treated (OVX-veh), and OVX 17beta-estradiol (E2)-treated (OVX-E2) Sprague-Dawley rats. Plasma norepinephrine (NE) was measured as an index of sympathetic activity. In sham-operated rats, ethanol caused significant decreases in mean arterial pressure that were associated with significant reductions in cardiac index and SV, whereas total peripheral resistance was not changed. Measured plasma NE levels were not affected by ethanol except for a significant reduction observed one time. OVX abolished the hypotensive effect of ethanol and the associated decreases in cardiac output, SV, and plasma NE. Treatment of OVX rats with E2 restored the hypotensive and sympathoinhibitory (decreases in plasma NE) responses to ethanol. Blood ethanol concentrations were not affected by OVX or subsequent E2 administration. These findings suggest that intragastric ethanol elicits estrogen-dependent decreases in blood pressure in female rats, which results mainly from a reduction in cardiac output. The mechanism by which ethanol elicits E2-dependent hypotension remains to be determined.

Ethanol counteraction of I1-imidazoline but not alpha-2 adrenergic receptor-mediated reduction in vascular resistance in conscious spontaneously hypertensive rats

Our recent findings have shown that ethanol selectively counteracts decreases in blood pressure (BP) evoked via activation of central I1-imidazoline receptors but not alpha-2 adrenoceptors in conscious spontaneously hypertensive rats (SHRs). This study investigated the role of sympathetic activity, cardiac output and total peripheral resistance (TPR) in the differential effect of ethanol on centrally mediated hypotension. Changes in plasma norepinephrine (NE), as index of sympathetic activity, BP, heart rate, cardiac index, stroke volume, and TPR elicited by rilmenidine or alpha-methylnorepinephrine (selective I1 and alpha-2 receptor agonists, respectively) and subsequent ethanol (0.5 or 1 g/kg) or saline, were evaluated in conscious SHRs. Intracisternal rilmenidine (25 microg) or alpha-methylnorepinephrine (alpha-MNE; 4 microg) elicited similar decreases in BP, TPR, and plasma NE, but cardiac index was not changed. Ethanol (0.5 g/kg i.v.) had no effect on hemodynamic responses to rilmenidine or alpha-MNE. The higher dose (1 g/kg i.v.) of ethanol counteracted the hypotensive response to rilmenidine and significantly (P <.05) elevated TPR and plasma NE. In contrast, ethanol (1 g/kg) had no effect on the hypotensive responses to alpha-MNE but significantly (P <.05) elevated plasma NE. However, this increase in NE was approximately one third of the increase evoked by ethanol when given after rilmenidine. These findings suggest that the selective counteraction by ethanol of the hypotension evoked via activation of central I1 but not alpha-2 receptors may relate, at least in part, to its greater ability to reverse the sympathoinhibition and the associated decrease in vascular resistance mediated by I1 receptors.

Acute hemodynamic effects of ethanol in conscious spontaneously hypertensive and normotensive rats

This study investigated the differential hemodynamic effects of small to high doses of ethanol in conscious age-matched spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKYs). Changes evoked by ethanol (0.25, 0.5, or 1 g/kg, i.v.) or equal volume of saline in mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), and total peripheral resistance (TPR) were followed for 90 min in the two rat strains. The baseline MAP (163 +/- 4 vs. 113 +/- 2 mm Hg) of SHRs was significantly (p < 0.05) higher, compared with WKYs due mainly to the presence of an elevated TPR 13.82 +/- 0.12 vs. 2.51 +/- 0.09 mm Hg/ml/min/100 g, p < 0.05) in SHRs. In both rat strains, all doses of ethanol produced immediate increases in MAP at 1 min, after which the MAP responses varied and depended on the rat strain and dose of ethanol used. In WKYs, 0.25 g/kg ethanol had no effect on MAP, but caused significant decreases in CO and SV and increased HR. Ethanol (0.5 and 1 g/kg) produced a short-lived (10 min) and dose-related increase in MAP. The higher dose (1 g/kg) of ethanol elicited significant (p < 0.05) increases in TPR that were counterbalanced by concomitant decreases in CO and SV. In SHRs, the two higher doses (0.5 and 1 g/kg) of ethanol elicited significant (p < 0.05) decreases and increases in MAP, respectively, compared with control (saline-treated) values. The pressor response to the 1 g/kg dose of ethanol was associated with an increase in TPR that achieved a statistical significance (p < 0.05) at 50 and 80 min after ethanol administration. HR was significantly (p < 0.05) reduced by the two higher doses of ethanol, whereas SV and CO were not changed. Blood ethanol concentrations measured 10, 30, and 60 min after ethanol administration were similar in SHRs and WKYs. These findings suggest that acute administration of ethanol to conscious rats elicits hemodynamic responses that are strain- and dose-dependent. In contrast to a short-lived and dose-related pressor response in WKYs, ethanol (0.5 and 1 g/kg) elicited opposite and longer lasting effects on MAP (decreases and increases, respectively) in SHRs. In both rat strains, the pressor response to the higher dose of ethanol was associated with an increase in TPR; an effect that was compromised by a concomitant decrease in CO in WKYs but not SHRs.

Synthesis of new thiolated acyclonucleosides with potential anti-HBV activity

Treatment of the sodium salt of compounds 1, 7 or 12 with chloroethyl methyl ether, 2-chloroethyl toluoylate or 2-(2-chloro ethoxy)ethyl acetate afforded the corresponding derivatives 2, 3, 4, 8, 9, 13 and 14. Ammonolysis of 3, 4, 9 and 14 at room temperature gave the corresponding hydroxyalkyl derivatives 5, 6, 10, 11, and 15, respectively. Alkylation of 2,4-dithiouracil gave 2,4-dialkylthio pyrimidine.

Ethanol selectively counteracts hypotension evoked by central I(1)-imidazoline but not alpha2-adrenergic receptor activation in spontaneously hypertensive rats

Previous studies from our laboratory showed that ethanol counteracts hypotensive responses to clonidine in spontaneously hypertensive rats. This study investigated whether this effect of ethanol involves interaction with central alpha2-adrenoceptors or I(1)-imidazoline receptors or both. The effects of ethanol (0.5 or 1 g/kg, i.v.) or an equal volume of saline on hypotensive and bradycardic responses to clonidine (mixed alpha2-adrenoceptor/I(1)-imidazoline receptor agonist), rilmenidine (selective I(1)-imidazoline receptor agonist), or alpha-methylnorepinephrine (selective alpha2-adrenoceptor agonist) were studied in conscious spontaneously hypertensive rats. Intracisternal administration of clonidine (0.5 microg), rilmenidine (25 microg), or alpha-methylnorepinephrine (4 microg) elicited similar decreases in mean arterial pressure (MAP; 25-30 mm Hg) that lasted > or =60 min. Subsequent administration of ethanol (0.5 and 1 g/kg, i.v.) counteracted the hypotensive effect of clonidine in a dose-related manner. Ethanol (1 g/kg) increased the blood pressure to levels similar to baseline (preclonidine) levels, and blood pressure remained significantly (p < 0.05) higher compared with the corresponding values in saline-treated rats. Similarly, ethanol (0.5 and 1 g/kg, i.v.) dose-dependently counteracted the hypotensive effect of rilmenidine. The antagonizing effects of ethanol on hypotension evoked by clonidine and rilmenidine were comparable in terms of both magnitude and duration. In contrast, ethanol (0.5 or 1 g/kg) had no effect on hypotension evoked by alpha-methylnorepinephrine. Except for a brief increase in blood pressure by ethanol (1 g/kg) at 5 min, blood pressure values obtained in alpha-methylnorepinephrine-treated rats receiving any of the two doses of ethanol were similar to postsaline values. Ethanol had no effect on bradycardic responses to any of the three hypotensive agents. Blood ethanol concentrations were similar regardless of the antihypertensive drug used. We concluded that the adverse hemodynamic effect of ethanol on centrally mediated hypotensive responses depends on the types of receptors involved in the elicitation of this response. That ethanol counteracts decreases in blood pressure evoked by clonidine and rilmenidine but not by alpha-methylnorepinephrine suggests an interaction between ethanol and central pathways involved in I(1)-imidazoline receptor-mediated hypotension.

Ethanol counteraction of clonidine-evoked inhibition of norepinephrine release in rostral ventrolateral medulla of rats

Previous studies from our laboratory demonstrated an antagonistic hemodynamic interaction between ethanol and clonidine in conscious and in urethane-anesthetized rats. The present study tested the hypothesis that ethanol produces its effect by counteracting clonidine-evoked inhibition of norepinephrine (NE) release at its major site of action, the rostral ventrolateral medulla (RVLM). In vivo electrochemical measurement of real-time changes in NE level in the RVLM of urethane-anesthetized Sprague-Dawley rats was made along with blood pressure and heart rate. Clonidine (30 microg/kg, i.v.) produced significant decreases (p < 0.05) in NE electrochemical signal and blood pressure. Ethanol (1 g/kg, i.v.) administered 10 min after clonidine significantly (p < 0.05) increased NE signal and counteracted clonidine-evoked hypotension. Equal volume of saline had no effect on NE signal in the RVLM nor on the hypotensive response to clonidine. Pretreatment with the same dose of ethanol (1 g/kg) caused slight increases in RVLM NE level and in blood pressure, but did not influence the electrochemical and blood pressure responses to clonidine; clonidine (30 microg/kg) administration 10 min after ethanol resulted in significant (p < 0.05) decreases in NE signal and blood pressure. These findings suggest that: (i) ethanol counteraction of the hypotensive action of clonidine involves, at least in part, opposite effects on central pathways that use NE as a neurotransmitter; (ii) the RVLM represents a possible site for the adverse hemodynamic interaction between ethanol and clonidine; and (iii) ethanol-evoked increase in RVLM NE, which correlates with its pressor effect, is much enhanced when RVLM NE level is reduced by clonidine.

The organophosphate pesticide chlorpyrifos affects form deprivation myopia

PURPOSE

The effects of the anti-cholinesterase organophosphate pesticide chlorpyrifos (CPF) on the refractive development of the eye were examined. Form deprivation was used to induce eye growth to address the previously reported relationship between organophosphate pesticide use and the incidence of myopia.

METHODS

Chickens, a well-established animal model for experimental myopia and organophosphate neurotoxicity, were dosed with chlorpyrifos (3 mg/kg per day, orally, from day 2 to day 9 after hatching) or corn oil vehicle (VEH) with or without monocular form deprivation (MFD) over the same period. The set of dependent measures included the refractive state of each eye measured using retinoscopy, axial dimensions determined with A-scan ultrasound, and intraocular pressure.

RESULTS

Dosing with CPF yielded an inhibition of 35% butyrylcholinesterase in plasma and 45% acetylcholinesterase in brain. MFD resulted in a significant degree of myopia in form-deprived eyes resulting from significant lengthening of the vitreal chamber of the eye. CPF significantly reduced the effect of MFD, resulting in less myopic eyes (mean refraction: VEH-MFD = -16.2 +/- 2.3 diopters; CPF-MFD = -11.1 +/- 1.8 diopters) with significantly shorter vitreal chambers. Nonoccluded eyes were, on average, slightly hyperopic. Treatment with CPF for 1 week in the absence of MFD led to no significant change in ocular dimensions or refraction relative to controls.

CONCLUSIONS

The use of form deprivation as a challenge suggests that CPF treatment interferes with the visual regulation of eye growth.

Ovariectomy abolishes ethanol-induced impairment of baroreflex control of heart rate in conscious rats

Our previous studies have shown that ethanol attenuates baroreflex control of heart rate in male rats. The present study investigated whether this effect of ethanol is gender-related, and whether it involves hormonal factors. The effect of intragastric administration of ethanol or equal volume of water on baroreflex-mediated decreases in heart rate in response to increments in blood pressure evoked by phenylephrine were evaluated in conscious age-matched male and female Sprague-Dawley rats as well as in ovariectomized rats. Baroreflex curves relating changes in blood pressure and associated heart rate responses were constructed, and the slopes of the regression lines were taken as a measure of baroreflex sensitivity. Phenylephrine (1-16 microg kg(-1), i.v.) elicited dose-dependent pressor responses that were similar in all groups of rats. However, the associated reflex bradycardic responses depended on the rat preparation and the dose of ethanol employed. In water-treated (control) animals, significantly (P < 0.05) lesser reflex bradycardic responses were observed in female compared with male rats (baroreflex sensitivity, -1.21 +/- 0.12 vs. -1.67 +/- 0.12 beats min(-1) mmHg(-1)). Ovariectomy resulted in a further reduction in baroreflex sensitivity (-0.82 +/- 0.06 beats min(-1) mmHg(-1)), suggesting a favorable role for ovarian hormones in baroreflex modulation. In male rats, ethanol (0.25, 0.5, or 1 g kg(-1), intragastric) elicited dose-related decreases in reflex bradycardic responses. The reduction in the regression coefficient obtained by the two higher doses (0.5 and 1 g kg(-1)) of ethanol was statistically significant compared with control values. The ability of ethanol to reduce baroreflex sensitivity appears to be gender-independent as it was similarly demonstrated in intact female rats. In contrast, ethanol had no effect on reflex bradycardic responses in ovariectomized rats at any of the doses tested. The data suggest that ethanol reduces baroreflex control of heart rate irrespective of the rat gender. Further, the lack of an effect of ethanol on baroreflex sensitivity in ovariectomized rats may suggest a role for ovarian hormones in ethanol-evoked baroreflex attenuation.

Estrogen enhances baroreflex control of heart rate in conscious ovariectomized rats

In previous studies, we have shown that the baroreflex control of heart rate is significantly attenuated in females compared with age-matched males. This study investigated the role of estrogen in the modulation of baroreflex function in conscious unrestrained rats. Baroreflex-mediated decreases in heart rate in response to increments in blood pressure evoked by phenylephrine were evaluated in conscious freely moving male and female Sprague-Dawley rats as well as in ovariectomized rats. The effect of a 2-day 17 beta-estradiol (50 micrograms.kg-1.day-1, s.c.) or vehicle treatment on baroreflex sensitivity was investigated in ovariectomized rats. Intravenous bolus doses of phenylephrine (1-16 micrograms/kg) elicited dose-dependent pressor and bradycardic responses in all groups of rats. Regression analysis of the baroreflex curves relating increments in blood pressure to the associated heart rate responses revealed a significantly (p < 0.05) smaller baroreflex sensitivity in female compared with male rats (-1.22 +/- 0.07 and -1.85 +/- 0.15 beats.min-1.mmHg-1, respectively), suggesting an attenuated baroreflex function in females. In age-matched ovariectomized rats, baroreflex sensitivity showed further reduction (-0.93 +/- 0.02 beats.min-1.mmHg-1). Treatment of ovariectomized rats with 17 beta-estradiol significantly (p < 0.05) enhanced the baroreflex sensitivity (-1.41 +/- 0.16 beats.min-1.mmHg-1) to a level that was slightly higher than that of sham-operated female rats. Furthermore, baroreflex sensitivity of ovariectomized estradiol-treated rats was not significantly different from that of age-matched male rats. The vehicle, on the other hand, had no effect on baroreflex sensitivity of ovariectomized rats. These data support our earlier findings that sexual dimorphism exists in baroreflex control of heart rate. More importantly, the present study provides experimental evidence that suggests a facilitatory role for estrogen in the modulation of baroreflex function.

Role of cardiac output in ethanol-evoked attenuation of centrally mediated hypotension in conscious rats

Our previous studies have shown that ethanol selectively counteracts centrally mediated hypotensive responses. This study investigated the role of cardiac output and peripheral resistance in the antagonistic interaction between ethanol and antihypertensive drugs. Changes in blood pressure, heart rate, cardiac index, stroke volume, and peripheral resistance elicited by clonidine and subsequent ethanol or saline administration were evaluated in conscious rats. The aortic barodenervated rat was employed because it exhibits greater hypotensive responses to clonidine compared with the intact rat. Aortic barodenervation elicited acute rises in blood pressure, heart rate, and peripheral resistance, whereas cardiac index and stroke volume were not altered. The blood pressure of conscious aortic barodenervated rats returned to sham-operated levels by 48 hours due to concomitant reductions in cardiac index and stroke volume; the peripheral resistance, however, remained significantly elevated. Clonidine (30 microg/kg, I.V.) elicited greater decreases in blood pressure in aortic barodenervated compared with sham-operated rats. The hypotension was caused by decreases in cardiac index and stroke volume because peripheral resistance did not change. Ethanol (1 g/kg, I.V.) counteracted the hypotensive effect of clonidine and raised blood pressure to levels higher than preclonidine values. Significant (P<.05) increases in cardiac index and stroke volume and decreases in peripheral resistance accompanied the pressor effect of ethanol. Additional control groups were included in the study to determine the selectivity of the interaction. A dose of hydralazine (0.5 mg/kg, I.V.) was used that produced similar hypotension to that evoked by clonidine in aortic barodenervated rats. Hydralazine-evoked hypotension was similar in denervated and control rats and resulted from significant reductions in peripheral resistance. Reflex increases in heart rate and stroke volume and hence cardiac output were observed. Ethanol given after hydralazine produced a short-lived pressor effect (<5 minutes versus 40 minutes in the case of clonidine) and counteracted the sympathetically mediated increases in cardiac output, stroke volume, and heart rate. These findings support our hypothesis that ethanol selectively counteracts hypotensive responses of central origin by reversing the reduction in cardiac output elicited by clonidine.

Aortic barodenervation up-regulates alpha2-adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla: an autoradiographic study

Earlier findings have shown that alpha2-adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla modulate baroreflexes. The present study investigated whether attenuation of baroreflexes induced by surgical interruption of aortic baroafferents is related to an alteration of alpha2-adrenoceptor binding in these regions of the brainstem. In vitro autoradiography was utilized to assess the density and binding dissociation constant (affinity) of alpha2-adrenoceptors in the rostral ventrolateral medulla and in the middle and rostral portions of the nucleus tractus solitarius of aortic-barodenervated and sham-operated rats. Compared to sham operation, aortic barodenervation caused an acute rise in mean arterial pressure and heart rate and a significant reduction in baroreflex sensitivity. Two days later, mean arterial pressure and heart rate of conscious aortic-barodenervated rats subsided to sham-operated levels, whereas the baroreflex sensitivity remained significantly (P<0.05) reduced when measured by phenylephrine (0.55+/-0.08 vs 1.26+/-0.07 ms/mmHg) or nitroprusside (0.43+/-0.06 vs 1.01+/-0.09ms/mmHg). Examination of brainstem coronal sections obtained from separate groups of rats 48 h after surgery and preincubated with [3H]rauwolscine (0.5-16 nM) revealed that labeling of alpha2 binding sites was saturable and of high affinity. Scatchard analysis of the saturation isotherms obtained from the three brain areas of sham-operated rats showed an uneven distribution of alpha2 binding sites; the rostral nucleus tractus solitarius exhibited the highest density and lowest affinity. Aortic barodenervation caused region-dependent changes in the binding activity of alpha2-adrenoceptors. These changes comprised significant (P<0.05) increases in the density of alpha2-adrenoceptors in the middle nucleus tractus solitarius (436+/-60 vs 240+/-50 fmol/mg protein) and rostral ventrolateral medulla (350+/-67 vs 194+/-35 fmol/mg protein) compared with sham-operated rats; no significant changes occurred in the rostral nucleus tractus solitarius. The affinity of alpha2 binding sites was not changed by aortic barodenervation in any of the three brain regions. These findings suggest that attenuation of baroreflexes produced by aortic barodenervation coincides with up-regulation of alpha2-adrenoceptors in brainstem areas that play critical roles in the control of cardiovascular functions.

Contrasting effects of urethane, ketamine, and thiopental anesthesia on ethanol-clonidine hemodynamic interaction

In previous studies, we have shown that ethanol counteracts the hypotensive and sympathoinhibitory effects of clonidine in conscious rats but enhances these responses in alpha-chloralose anesthetized rats. This study investigated whether the latter finding pertains to other anesthetics that act by different mechanisms. The hemodynamic interaction between clonidine and ethanol was evaluated in conscious aortic barodenervated rats and in rats anesthetized with urethane, ketamine, or thiopental. The conscious aortic barodenervated rat was used because it exhibits a greater hypotensive response to clonidine compared with intact (sham-operated) rats. Starting from similar baseline values of blood pressure (BP) and heart rate, clonidine (30 micrograms/kg, iv) elicited similar decreases in BP in all groups of rats (conscious aortic barodenervated or anesthetized). Subsequent administration of ethanol (1 g/kg, iv) counteracted the hypotensive effect of clonidine in conscious aortic barodenervated rats and raised the BP to levels higher than the baseline (preclonidine) values. The pressor effect of ethanol persisted for at least 30 min. In contrast, preadministration of ethanol had no effect on the hypotensive effect of the subsequently administered clonidine. The antagonistic clonidine-ethanol hemodynamic interaction in conscious rats was not altered in urethane-anesthetized rats, both in terms of magnitude and duration. In ketamine-anesthetized rats, a short lasting (< 10 min) pressor effect of ethanol was observed. In contrast, ethanol augmented the hypotensive effect of clonidine in thiopental-anesthetized rats; the hypotensive effect of clonidine became slightly but significantly (p < 0.05) greater after ethanol compared with respective time control values. These findings suggest that the adverse hemodynamic effect of ethanol on centrally mediated hypotensive response is modified by different anesthetics. The antagonistic hemodynamic interaction, demonstrated in conscious rats, is replicated in urethane-anesthetized rats but weakened and reversed in ketamine- and thiopental-anesthetized rats, respectively. Therefore, urethane-anesthetized rats may be used in mechanistic studies on the antagonistic ethanol-clonidine hemodynamic interaction that cannot be undertaken, for technical reasons, in conscious rats.

Ethanol microinjection into the area postrema selectively attenuates baroreflex sensitivity measured by vasopressin in conscious rats

Microinjection of ethanol (10 microg) into the area postrema (AP) of conscious rats attenuated baroreflex sensitivity (BRS) measured by arginine vasopressin (AVP) (-1.73 +/- 0.13 versus -2.47 +/- 0.16 bpm/mmHg), but not by phenylephrine (PE) (-1.94 +/- 0.26 versus -1.82 +/- 0.20 bpm/mmHg). Intra-AP injection of the V1 receptor antagonist D(CH2)5Tyr(Me)AVP replicated the differential effects of ethanol on BRS measured by AVP (-1.89 +/- 0.11 versus -2.52 +/- 0.10 bpm/mmHg) and PE (-2.10 +/- 0.12 versus -2.09 +/- 0.19 bpm/mmHg). Intra-AP artificial cerebrospinal fluid (ACSF) did not change BRS measured by AVP or PE. These data suggest that ethanol attenuates the facilitatory action of AVP on baroreflexes via its interaction with AVP neurons in the AP.

Increased neurotoxicity following concurrent exposure to pyridostigmine bromide, DEET, and chlorpyrifos

The operating environment of the service personnel during the Persian Gulf War involved psychological, biological, and chemical elements including exposure to pesticides such as the insect repellent DEET (N,N-diethyl-m-toluamide) and the insecticide chlorpyrifos (O,O-diethyl O-3,5,6-trichloropyridinyl phosphorothioate) and to pyridostigmine bromide (PB,3-dimethylaminocarbonyloxy-N-methylpyridinium bromide) that was administered as a prophylactic agent against possible nerve gas attack. The present study was designed to determine the toxicity produced by individual or coexposure of hens 5 days/week for 2 months to 5 mg PB/kg/day in water, by gavage; 500 mg DEET/kg/day, neat, sc; and 10 mg chlorpyrifos kg/day in corn oil, sc. Coexposure to various binary treatments produced greater neurotoxicity than that caused by individual exposures and was characterized by severe neurologic deficit and neuropathological alterations. Also, neurotoxicity was further enhanced following concurrent administration of the three chemicals. Severe inhibition of plasma butyrylcholinesterase (BuChE) activity was produced in hens treated with PB (activity 17% of control) compared to those treated with chlorpyrifos (activity 51% of control) or DEET (activity 83% of control). BuChE inhibition was further increased in binary and tertiary treatment groups compared to individual treatment groups. In contrast, a significant inhibition of brain acetylcholinesterase (AChE) was produced in hens administered chlorpyrifos alone (activity 67% of control), while those given chlorpyrifos in combination with other compounds exhibited a significant inhibition of brain AChE activity ranging from 43 to 76%. Brain neurotoxicity target esterase (NTE) was not inhibited in any of the individual treatment groups or PB/DEET, but was significantly inhibited and had activity expressed as a percentage of control in groups administered combined chlorpyrifos with PB of 73% or DEET of 74% and in the tertiary treatment group of 71%. We hypothesize that test compounds may compete for xenobiotic metabolizing enzymes in the liver and blood and may also compromise the integrity of the blood-brain barrier, leading to an increase in their "effective concentrations" in the nervous system to levels equivalent to the toxic doses of individual compounds. This is consistent with the present observation of increases in (1) the inhibition of brain AChE and NTE, (2) the extent of neurologic dysfunction, and (3) the severity and frequency of neuropathologic lesions in the combined treatment groups compared to those administered individual compounds.

Synergistic behavioral interaction between ethanol and clonidine in rats: role of alpha-2 adrenoceptors

Activation of central alpha-2 adrenoceptor leads to a sleep-like state. The present study investigated the effect of ethanol on the loss of the righting reflex (LORR) and hypotension evoked by clonidine in Sprague-Dawley rats. Clonidine at 30 micrograms/kg had no effect on righting reflex, but a higher dose (60 micrograms/kg) elicited variable LORR that averaged 6.5 +/- 4.1 min. Similarly, 0.5 g/kg of ethanol elicited little effect (0.17 +/- 0.17 min), but a higher dose (1 g/kg) produced 2.5 +/- 1.1 min of LORR. Ethanol (0.5 g/kg), combined with the lower dose of clonidine, still had little effect on LORR, but when combined with the higher dose of clonidine the LORR (34.8 +/- 6.5 min) became significantly (P < .01) greater than the sum of the individual effects. Similarly, rats that received a combination of the higher dose (1 g/kg) of ethanol and lower dose (30 micrograms/kg) of clonidine exhibited significantly (P < .01) greater LORR (18.6 +/- 2.5 min) than the sum of individual effects. These findings suggest a synergistic interaction that is dose-related. The alpha-2 adrenoceptor antagonist yohimbine (1 mg/kg), or a mixed antagonist of imidazoline and alpha-2 adrenoceptors, idazoxan (60 micrograms/kg), counteracted the synergistic interaction between ethanol and clonidine on LORR; yohimbine was more effective than idazoxan, but the difference was not significant. Ethanol counteracted the hypotensive effect of clonidine and significantly (P < .05) increased blood pressure to levels higher than preclonidine and corresponding control values. Therefore, the synergistic interaction on LORR cannot be accounted for by an enhanced hypotensive response to clonidine. Furthermore, idazoxan counteracted the hypotensive response to clonidine more effectively than did yohimbine. Taken together, the findings suggest: 1) ethanol differentially influences the sedative (synergistic interaction) and hypotensive (antagonistic interaction) effects of clonidine; 2) the synergistic behavioral interaction is dose-related and involves, at least in part, central alpha-2 adrenoceptors; and 3) the hypotensive effect of clonidine is primarily mediated via imidazoline receptors.

Structure-activity relationships for the binding of arylpiperazines and arylbiguanides at 5-HT3 serotonin receptors

Arylpiperazines are nonselective agents that bind at 5-HT3 serotonin receptors with moderate to high affinity, whereas 1-phenylbiguanide is a low-affinity but more selective 5-HT3 agonist. In an attempt to enhance the affinity of the latter agent, and working with the assumption that similarities might exist between the binding of the two types of agents, we formulated structure-activity relationships for the binding of the arylpiperazines and then incorporated those substituents, leading to high affinity for the arylpiperazines, into 1-phenylbiguanide. A subsequent investigation examined the structure-activity relationships of the arylbiguanides and identified arylguanidines as a novel class of 5-HT3 ligands. Although curious similarities exist between the structure-activity relationships of the arylpiperazines, arylbiguanides, and arylguanidines, it cannot be concluded that all three series of compounds are binding in the same manner. Furthermore, upon investigating pairs of compounds in the three series, the arylpiperazines behaved as 5-HT3 antagonists (von Bezold-Jarisch assay) whereas the arylbiguanides and arylguanidines acted as 5-HT3 agonists.

Differential alteration of neuronal and cardiovascular responses to adenosine microinjected into the nucleus tractus solitarius of spontaneously hypertensive rats

We previously reported that adenosine elicited site-dependent neuronal and cardiovascular responses in two subareas of the nucleus tractus solitarius (NTS) of normotensive rats. Pressor and tachycardic responses were obtained from the rostral NTS (adenosine pressor system), and depressor and bradycardic responses were obtained from the caudal NTS (adenosine depressor system). In both areas, adenosine inhibited the firing rate of barosensitive neurons. The present study investigated whether spontaneously hypertensive rats (SHR) exhibit abnormal neuronal and cardiovascular responses mediated by the adenosine pressor and depressor systems within the NTS. Male SHR and Wistar-Kyoto rats (WKY) were anesthesized with urethane and prepared for blood pressure and heart rate recording, stereotaxic microinjection of adenosine into the NTS, and extracellular recording of single-unit neuronal activity of NTS neurons. Chemical identification of the targeted neuronal pool was made by L-glutamate (5 nmol) and confirmed by histology. SHR exhibited significantly higher mean arterial pressure and firing rate of caudal NTS neurons (45.0 +/- 4.5 versus 27.3 +/- 4.7 spikes per 2.5 seconds, P <.05) but similar heart rate and neuronal firing rate of rostral NTS neurons compared with WKY. Adenosine (0.1, 1, and 10 nmol) elicited dose-related neuronal and cardiovascular responses in both strains. However, SHR exhibited differential alterations in both adenosine systems. Compared with WKY, SHR exhibited attenuated pressor, tachycardic, and neuronal responses mediated by the adenosine pressor system and exaggerated depressor, bradycardic, and neuronal responses mediated by the adenosine depressor system. In both strains, the responses elicited by adenosine were virtually abolished by theophylline (10 mg/kg IV), suggesting that these responses were mediated by adenosine receptors in the NTS. Furthermore, the theophylline-evoked increase in blood pressure was twofold higher in SHR (15.0 +/- 1.7 versus 6.9 +/- 1.5 mm Hg, P <.05); larger but nonsignificant increases in heart rate and neuronal firing rate also were evident in SHR compared with WKY. These findings suggest differential alterations in adenosine pressor and depressor systems in the NTS of SHR, which may be implicated in the pathophysiology of this model of hypertension.

Upregulation of imidazoline receptors in the medulla oblongata accounts for the enhanced hypotensive effect of clonidine in aortic barodenervated rats

The present study tested the hypothesis that an upregulation of the imidazoline receptor in the rostral ventrolateral medulla (RVLM) of aortic barodenervated (ABD) rats may account for the enhanced hypotensive effect of clonidine. In vitro autoradiographic radioligand binding studies were utilized to investigate the binding characteristics of imidazoline receptors in the RVLM and nucleus tractus solitarius (NTS), areas that play critical roles in cardiovascular regulation and elicitation of clonidine responses. ABD but not sham operation (SO) caused immediate and significant (P < 0.05) increases in mean arterial pressure (MAP) and heart rate (HR) and an impairment of the baroreflex-mediated HR response (baroreflex sensitivity, BRS). Two days after ABD, these parameters, except BRS, subsided to near-control (SO) levels. Intracisternal (i.c.) administration of clonidine (0.1 micrograms) elicited a 3-fold greater decrease in BP of conscious ABD compared with SO rats (-20.3 +/- 2.6 vs. -7.4 +/- 0.9 mmHg) thus demonstrating the ability of ABD to enhance centrally-mediated hypotensive responses. Autoradiographic visualization of brain sections obtained from separate groups of ABD and SO rats 48 h after surgery preincubated with [3H]idazoxan (2.5-3.5 nM) showed that [3H]idazoxan binding in RVLM, middle NTM (mNTS) and rostral NTS (rNTS) was saturable and of high affinity. Uneven distribution of imidazoline binding sites was evident since in control (SO) rats, Scatchard analysis of binding data revealed similar densities (Bmax) of [3H]idazoxan binding sites in the RVLM and mNTS versus significantly higher density in the rNTS. In ABD rats, the binding dissociation constant (Kd) was significantly decreased in both the RVLM (8.1 +/- 3.1 vs. 21.4 +/- 5.0 nM) and rNTS (12.3 +/- 1.3 vs. 18.6 +/- 3.1 nM) compared with SO rats while the Bmax was not affected. This finding suggests an increased receptor affinity in the RVLM and rNTS of barodenervated rats. The mNTS of ABD rats exhibited significant increases in the Bmax (861 +/- 96 vs. 570 +/- 87 fmol/mg protein) compared with values of SO rats but the receptor affinity was not affected. It is concluded that: (i) aortic baroreceptors exert a tonic inhibitory influence on central imidazoline receptor function; and (ii) the enhanced hypotensive effect of clonidine in conscious ABD rats may be accounted for by the increased affinity of the medullary imidazoline receptors particularly in the RVLM.

Toxicokinetics of a single 50 mg/kg oral dose of [2,3-14C]acrylamide in White Leghorn hens

A single oral dose of [2,3-14C]acrylamide (50 mg/kg) was administered in water to adult white leghorn hens. Seven groups of three hens were euthanized between 2 and 120 hr after administration. Within 12 hr, the hens excreted 70% of the administered dose, and more than 99% within 48 hr. Blood, plasma, liver, and muscle contained the greatest percentage of administered dose at 4 hr after dosing. Less than 0.02% of the administered dose appeared in brain at any time. Radiolabel accumulated in the eggs, with 0.52% of the administered dose accumulated within 5 days. Binding of radiolabel to erythrocytes was minimal. Elimination of radiolabel from all tissues was biphasic. Terminal elimination half-lives for 14C were longer than 10 days, at which time less than 0.2% of the administered dose remains in the tissues. Distribution half-lives for 14C were longest for whole blood and shortest for kidney. Radioactivity in the blood and plasma reached a peak at between 4 and 12 hr. Most of this radioactivity was identified as acrylamide, which disappeared biexponentially with terminal elimination half-lives longer than 10 days. Distribution half-lives for acrylamide were longest in brain and shortest in whole blood. These results show that orally administered acrylamide is poorly absorbed and rapidly eliminated from hens and accumulates in their eggs in a nonextractable form.