Protein kinase C -activating isophthalate derivatives mitigate Alzheimer's disease-related cellular alterations

Abnormal protein kinase C (PKC) function contributes to many pathophysiological processes relevant for Alzheimer's disease (AD), such as amyloid precursor protein (APP) processing. Phorbol esters and other PKC activators have been demonstrated to enhance the secretion of soluble APPα (sAPPα), reduce the levels of β-amyloid (Aβ), induce synaptogenesis, and promote neuroprotection. We have previously described isophthalate derivatives as a structurally simple family of PKC activators. Here, we characterised the effects of isophthalate derivatives HMI-1a3 and HMI-1b11 on neuronal viability, neuroinflammatory response, processing of APP and dendritic spine density and morphology in in vitro. HMI-1a3 increased the viability of embryonic primary cortical neurons and decreased the production of the pro-inflammatory mediator TNFα, but not that of nitric oxide, in mouse neuron-BV2 microglia co-cultures upon LPS- and IFN-γ-induced neuroinflammation. Furthermore, both HMI-1a3 and HMI-1b11 increased the levels of sAPPα relative to total sAPP and the ratio of Aβ42/Aβ40 in human SH-SY5Y neuroblastoma cells. Finally, bryostatin-1, but not HMI-1a3, increased the number of mushroom spines in proportion to total spine density in mature mouse hippocampal neuron cultures. These results suggest that the PKC activator HMI-1a3 exerts neuroprotective functions in the in vitro models relevant for AD by reducing the production of TNFα and increasing the secretion of neuroprotective sAPPα.

Labelling, molecular modelling and biological evaluation of vardenafil: a potential agent for diagnostic evaluation of erectile dysfunction

^99mTc-tricarbonyl-vardenafil was specifically radiosynthesized for diagnostic evaluation of erectile dysfunction with a radiochemical yield ~97.2%. It was stable in saline up to 15h and in serum for more than 6h. The radiocomplex was lipophilic with a partition coefficient ~1.32 and plasma protein binding 72-76%. Its structure was determined using molecular mechanics and confirmed by NMR. In-silico docking to its target PDE₅ enzyme was performed. The radiocomplex inhibitory activity was assessed and its IC₅₀ was 0.7nM. Biodistribution in normal rats and biological evaluation in rat models of erectile dysfunction were performed. The results strongly suggested that ^99mTc-tricarbonyl-vardenafil is a good candidate to image erectile dysfunction in humans.

[Effect of Catechol-O-methyltransferase deficiency on reinforcing effects of cocaine (experimental study)]

Catechol-O-methyltransferase (COMT) remains an important regulatory element in prefrontal cortex dopamine homeostasis. The literature data suggest that individual differences in COMT activity (Val158Met polymorphism) might have indirect downstream effects on the reward system. The aim of the present study was to examine whether COMT deletion affects reinforcing effects of cocaine in mice. The study was conducted in male mice with homozygous COMT deletion as well as their C57BL/6J wild-type littermates. Animals were trained to nose-poke to receive response-contingent intravenous infusions of cocaine (0.3 mg/kg per infusion; final schedule of reinforcement - fixed ratio (FR) 3 time out 30 s). Following the initial acquisition phase, cocaine self-administration dose-effect functions (0.03, 0.1, 0.3, 1, and 3 mg/kg per infusion) were determined under FR3 and progressive ratio (PR) schedules of reinforcement. Cocaine dose-dependently maintained responding under FR3 and PR schedule of reinforcement when the unit dose of cocaine was varied across the sessions. The total cocaine intake did not differ in COMT deletion mice and wild-type mice. The results of this study suggest that individual differences in COMT activity do not affect primary reinforcing effects of cocaine in mice.

Cotinine binding to nicotinic acetylcholine receptors in bovine chromaffin cell and rat brain membranes

Cotinine is the major metabolite of nicotine. It has nicotine-like biological activity, but its potency is low. We studied cotinine binding to nicotinic receptors labelled with [3H]epibatidine. In membranes from cultured bovine chromaffin cells [3H]epibatidine bound to two apparent sites with K(d) values of 93 and 1400 pM. The low-affinity binding represented two-thirds of the binding sites. In rat frontal cortex and hippocampus homogenate membranes, only one apparent binding site was detected. The Kd values were 40 and 62 pM, in frontal cortex and hippocampus, respectively. Nicotine displaced [3H]epibatidine 10 times more potently from the brain than from the chromaffin cell membranes, and cotinine had over two orders of magnitude lower affinity than nicotine. In addition, the competitive nicotinic receptor antagonists methyllycaconitine and dihydro beta-erythroidine displaced [3H]epibatidine (100 pM and 1 nM) from the chromaffin cell membranes. Alpha-bungarotoxin did not affect the binding of 100 pM [3H]epibatidine. However, upon labelling with 1 nM [3H]epibatidine alpha-bungarotoxin (10 nM to 10 microM) displaced one-sixth of the bound radioligand. Our results demonstrate that 100 pM to 1 nM [3H]epibatidine labels mostly neuronal heteropentameric nicotinic receptors in bovine chromaffin cell membranes, and that cotinine is a low-affinity nicotinic ligand both in the adrenal chromaffin cell and in the brain receptors.

Hydrogen peroxide attenuates store-operated calcium entry and enhances calcium extrusion in thyroid FRTL-5 cells

Redox modulation participates in the regulation of intracellular free calcium concentration ([Ca(2+)](i)) in several cell types. In thyroid cells, including FRTL-5 cells, changes in [Ca(2+)](i) regulate several important functions, including the production of H(2)O(2) (hydrogen peroxide). As H(2)O(2) is of crucial importance for the production of thyroid hormones, we investigated the effects of H(2)O(2) on [Ca(2+)](i) in thyroid FRTL-5 cells. H(2)O(2) itself did not modulate basal [Ca(2+)](i). However, H(2)O(2) attenuated store-operated calcium entry evoked by thapsigargin, both in a sodium-containing buffer and in a sodium-free buffer. The effect of H(2)O(2) was abrogated by the reducing agent beta-mercaptoethanol. H(2)O(2) also attenuated the thapsigargin-evoked entry of barium and manganese. The effect of H(2)O(2) was, at least in part, mediated by activation of protein kinase C (PKC), as H(2)O(2) enhanced the binding of [(3)H]phorbol 12,13-dibutyrate. H(2)O(2) also stimulated the translocation of the isoenzyme PKCepsilon from the cytosolic fraction to the particulate fraction. Furthermore, H(2)O(2) did not attenuate store-operated calcium entry in cells treated with staurosporine or calphostin C, or in cells with down-regulated PKC. H(2)O(2) depolarized the membrane potential in bisoxonol-loaded cells and when patch-clamp in the whole-cell mode was used. The depolarization was attenuated in cells with down-regulated PKC. This depolarization, at least in part, explained the H(2)O(2)-evoked inhibition of calcium entry. In addition, H(2)O(2) enhanced the extrusion of calcium from cells stimulated with thapsigargin and this effect was abolished in cells with down-regulated PKC and after treatment of the cells with the reducing agent beta-mercaptoethanol. In conclusion H(2)O(2) attenuates an increase in [Ca(2+)](i). As H(2)O(2) is produced in thyroid cells in a calcium-dependent manner, our results suggest that H(2)O(2) may participate in the regulation of [Ca(2+)](i) in these cells via a negative-feedback mechanism involving activation of PKC.

3-Cloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a rat thyroid gland carcinogen, does not affect serum levels of TSH and thyroid hormones

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a chlorine disinfection by-product in drinking water, causes follicular adenomas and carcinomas in thyroid glands of Wistar rats with an unknown mechanism. We evaluated effects of MX on blood thyroid stimulating hormone (TSH), thyroxine (T(4)), triiodothyronine (T(3)), prolactin (PRL) and growth hormone (GH) levels in male and female Wistar rats to assess their role in the tumorigenesis. The levels of TSH, PRL and GH in serum of male rats were not significantly affected by a single dose of 1, 10 or 60 mg/kg of MX administered by gavage 2 h before sampling. In repeated dose experiments MX was administered at dose levels of 1, 10 or 60 mg/kg of MX (40 mg/kg for females) in water by gavage daily for 1 or 3 weeks. Thyroid glands, adrenal glands and the liver were evaluated for morphological changes and cell proliferation activity after staining with proliferating cell nuclear antigen (PCNA). The dose of 60 mg/kg MX was toxic upon repeated administration. Nevertheless, MX did not affect blood TSH and T(4) levels at any time point in either sex. T(3) concentration increased transiently in males (by 37% after week 1) at the highest MX dose but not in females. MX did not change the weights of thyroid glands, their morphology and cell proliferation activity by the end of the week 3. MX did not affect blood PRL levels but decreased GH levels in males at all doses after the first week of MX treatment. The results indicate that MX does not alter blood TSH and thyroid hormone levels in rats, and imply that MX may not cause thyroid follicular cell tumors by TSH-mediated hormonal promotion.

Cotinine and nicotine inhibit each other's calcium responses in bovine chromaffin cells

Cotinine is the major metabolite of nicotine. It has some biological activity, but its pathophysiological effects are largely unclear. We studied whether cotinine initiates calcium transients or affects those induced by nicotine. In bovine adrenal chromaffin cells labeled with the fluorescent calcium indicator Fura 2, cotinine (0. 32-3.2 mM) concentration-dependently increased the intracellular Ca(2+) concentration ([Ca(2+)](i)). The effect was abolished by omitting extracellular Ca(2+) during the stimulations. Also nicotinic receptor channel blockers hexamethonium (10 microM-1 mM) and chlorisondamine (100 microM), as well as a competitive nicotinic receptor antagonist dihydro-beta-erythroidine (10-100 microM), inhibited the response. Cotinine (0.32-3.2 mM) preincubation for 2 min inhibited both the nicotine-induced and the cotinine-induced increases in [Ca(2+)](i). Also nicotine (3.2-10 microM) inhibited the cotinine-induced increase in [Ca(2+)](i). Tetrodotoxin (1 microM) and thapsigargin (1 microM) pretreatments did not affect the responses to cotinine, while 300 nM nimodipine partially inhibited the cotinine-induced increase in [Ca(2+)](i). The results indicate that cotinine has nicotine-like effects on chromaffin cells. It may also desensitize the nicotinic cholinergic receptors, possibly by acting as a low-affinity agonist at these receptors.

Hypothalamic histamine, growth rate, plasma prolactin and growth hormone levels in rats with long-term portacaval anastomosis

OBJECTIVE AND DESIGN

Histamine can modulate feeding behaviour and hormone release; therefore we examined the hypothalamic histamine system, the growth pattern and the serum levels of prolactin and growth hormone in rats with portacaval anastomosis (PCA).

MATERIAL

The growth rate of 30 PCA- and 30 sham-operated male Han:Wistar rats was monitored for 6 months. Thirteen sham and 9 PCA rats were used for biochemical studies.

METHODS

Histamine was assayed by HPLC, tele-methylhistamine by GC-MS, prolactin and growth hormone by RIA. Student's t-test was used to compare the groups.

RESULTS

Six months after surgery, the PCA rats exhibited marked growth retardation (weight gain of 20 g vs. 140 g for the sham rats; p < 0.001), increased plasma levels of prolactin (9.7 +/- 2.4 vs. 3.6 +/- 0.6; p<0.01) and unaltered growth hormone levels (6.2 +/- 0.5 vs. 8.1 +/- 1.0). A six-fold elevation of histamine concentration (29.5 +/- 3.9 vs. 4.8 +/- 0.4; p<0.001) and a two-fold increase of tele-methylhistamine levels (1.8 +/- 0.1 vs. 0.8 +/- 0.02; p<0.001) were found in hypothalamus.

CONCLUSION

We suggest that increased histaminergic activity in the hypothalamus may be involved in the development of growth retardation and in the enhanced basal secretion of prolactin in male rats with long-term PCA.

Inhibition of nicotinic responses by cotinine in bovine adrenal chromaffin cells

We studied the effects of cotinine, the major metabolite of nicotine, on nicotine-induced increase in [3H]phorbol dibutyrate binding, activation of protein kinase C and [3H]noradrenaline release in primary cultured bovine adrenal chromaffin cells. Cotinine (1 mM, 15 min.) and nicotine (10 microM, 5 min.) increased the [3H]phorbol binding by 100% and 150%, respectively. Both a short-term (10 min.) and a long-term (24 hr) pretreatment with cotinine inhibited the effect of nicotine. A 24 hr pretreatment with cotinine (1 mM) also reduced the nicotine-induced increase in membrane-bound protein kinase C activity. Cotinine pretreatment (10 min.) dose-dependently inhibited the release of [3H]noradrenaline induced by nicotine and dimethylphenylpiperazinium. Cotinine pretreatment did not reduce the [3H]noradrenaline release induced by high extracellular potassium (56 mM) or veratrine (10 mg l-1). The results indicate that cotinine inhibits activation of protein kinase C and noradrenaline release induced by nicotinic agonists in primary cultures of bovine adrenal chromaffin cells. The results suggest that pre-existing cotinine could modify responses to acute exposure to nicotine in neural systems.

Nicotine-like effects of cotinine on protein kinase C activity and noradrenaline release in bovine adrenal chromaffin cells

1. We studied the effect of cotinine, a slowly eliminated metabolite of nicotine, on protein kinase C (PKC) distribution and noradrenaline release in primary cultured bovine adrenal chromaffin cells. Changes in PKC activity were detected by [3H]-phorbol-12,13-dibutyrate binding, histone phosphorylation assay and by Western blot. 2. Cotinine (10-32 mM) increased phorbol binding to chromaffin cells in response to 10 min but not to 24 h exposure. The increased binding was reversed by a nicotinic antagonist hexamethonium (10 microM). 3. Cotinine (10 mM, 30 min) also increased membrane-associated PKC activity and membrane-associated PKC alpha and epsilon immunoreactivity. 4. Cotinine (0.1-32 mM for 10 s to 20 min) dose- and time-dependently increased the release of preloaded [3H]-noradrenaline from the cultured cells. The release increased with increasing duration of the contact period. In treatments lasting 1 min or longer, a peak effect was followed by a reduced response at higher concentrations. 5. We confirm the earlier findings that cotinine is biologically active, and conclude that its effects are at least partly mediated via nicotinic cholinergic receptors and through PKC.

Carcinogenicity of the drinking water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone in the rat

BACKGROUND

Several epidemiologic studies have suggested that the consumption of chlorinated drinking water may be associated with the development of certain cancers in humans. 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a byproduct of the chemical reactions that occur in chlorinated drinking water, has been found to be mutagenic in bacteria and mammalian cells; however, its potential to cause tumors in animals has not been tested previously.

PURPOSE

The objective of this study was to evaluate the carcinogenicity of MX in rats given MX in their drinking water.

METHODS

MX was administered to male and female Wistar rats (50 rats per dose group) in drinking water for 104 weeks at concentrations yielding the average daily doses of MX of 0.4 mg/kg of animal weight (low dose), 1.3 mg/kg (mid dose), and 5.0 mg/kg (high dose) for males and 0.6 mg/kg, 1.9 mg/kg, and 6.6 mg/kg for females, respectively. Control rats received water from the same source used for preparation of the MX dose formulations (after its adjustment to the same pH range). Body weight, clinical signs, and food and water consumption were recorded regularly. At the end of the treatment period, the animals were killed and full histopathologic analysis was performed on 47 tissues and all lesions.

RESULTS

Dose-dependent increases in tumor incidence were observed in rats given MX-containing drinking water; the same MX doses had no obvious toxic effects on animals. MX consumption increased most drastically the prevalence of follicular adenoma (up to 43% and 72% in high-dose males and females, a test [one-sided] for positive trend in all dose groups P = .0045 and P = .0000, respectively) and carcinoma (55% [P = .0000] and 44% [P = .0000], respectively) in thyroid glands and cholangioma in the liver (8% [P = .0009] and 66% [P = .0000] in the high-dose males and females, respectively). Among rats given the higher doses of MX in their drinking water, cortical adenomas of the adrenal glands were increased in both sexes, alveolar and bronchiolar adenomas of the lungs and Langerhans' cell adenomas of the pancreas were increased in males, and lymphomas, leukemias, and adenocarcinomas and fibroadenomas of the mammary glands were increased in females. Even the lowest MX dose studied was carcinogenic.

CONCLUSION

MX is a potent carcinogen in both male and female rats, and it causes tumors at doses that are not overtly toxic to rats.

IMPLICATIONS

Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor in the possible association between consumption of chlorinated drinking water and cancer in humans.

Role of protein kinase C in microglia-induced neurotoxicity in mesencephalic cultures

Microglial activation selectively kills certain neuron populations in mixed neuronal/glial cultures, which may prove useful for modeling neurodegenerative diseases such as Parkinson's disease. In mesencephalic mixed neuronal/glial cultures, microglial activation by zymosan A killed more dopaminergic neurons, assessed by [3H]dopamine uptake and by counting tyrosine hydroxylase-immunoreactive neuron number, than did microglial activation by lipopolysaccharide (LPS). The additional toxicity of zymosan resulted from microglial protein kinase C (PKC) activation. Both zymosan and PMA, but not LPS, activated PKC in enriched microglial preparations. In the mixed neuronal/glial cultures, activation of PKC by phorbol myristate acetate (PMA) increased LPS-induced nitric oxide (NO; by nitrite measurements), but not zymosan-induced NO production, and increased LPS-induced dopaminergic neurotoxicity, but not zymosan-induced dopaminergic neurotoxicity. Additive effects of PMA and LPS, similar to zymosan effects alone, reflected activation of distinct neurotoxic pathways in the microglia. The NO synthase inhibitor N-nitro-L-arginine methyl ester (NAME) totally blocked the neurotoxicity of LPS, and partially blocked zymosan-induced neurotoxicity; NAME did not block the PKC component of neurotoxicity. In addition to stimulating NO production as effectively as LPS, zymosan also activates microglial PKC and associated non-NO-mediated neurotoxic pathways that may be important in human neurodegenerative diseases. Since the role of NO in human microglia-induced neurotoxicity is controversial, zymosan may prove more useful than LPS as a microglial activator in the rodent mixed neuronal/glial culture model.

Evidence for cholecystokininA receptors in bovine adrenal chromaffin cells

We have studied a possible role of cholecystokinin (CCK) in regulating adrenal medullary function. Caerulein (10(-10)-10(-7) M), a CCK receptor agonist, increased formation of inositol phosphates in primary cultured bovine adrenal medullary (BAM) chromaffin cells in a concentration-dependent manner. The effect of caerulein was antagonized by devazepide, a selective CCKA-receptor antagonist, but not by L-365.260, a selective CCKB-receptor antagonist. These results suggest that BAM cells possess functional CCK receptors of the CCKA-subtype. Stimulation of these receptors with caerulein activates a signal transduction pathway via phospholipase C. CCK may regulate catecholamine release in BAM cells.

Cytotoxicity of macrolide antibiotics in a cultured human liver cell line

Cytotoxicity of erythromycin base, erythromycin estolate, erythromycin-11,12-cyclic carbonate, roxithromycin, clarithromycin and azithromycin was compared in cultured human non-malignant Chang liver cells using reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and cellular protein concentration as end points of toxicity. Erythromycin estolate was the most toxic macrolide in all tests differing clearly from all the other macrolides studied. Erythromycin-11,12-cyclic carbonate was also more toxic than the other macrolides. Roxithromycin and clarithromycin were the next toxic derivatives, while erythromycin base and azithromycin were least toxic. Thus, cytotoxicity of the new semisynthetic macrolides, roxithromycin, clarithromycin and azithromycin, is not substantially different from that of erythromycin base. In view of the low level of hepatotoxicity of macrolides hitherto reported in humans, the results do not suggest any substantial risk for hepatic disorders related to the use of azithromycin, clarithromycin and roxithromycin.

Morphine withdrawal alters anterior pituitary hormone secretion, brain endopeptidase activity and brain monoamine metabolism in the rat

Rats were made tolerant to morphine by a 5-day regimen with increasing doses. The time course of changes in serum anterior pituitary hormone levels, brain endo- and exopeptidase activity, levels of brain biogenic amines and body weight were studied during abrupt morphine withdrawal. Cold stimulated secretion of thyrotropin and the secretion of growth hormone were both decreased whereas that of prolactin was increased. In the hypothalamus both prolyl endopeptidase and dipeptidyl peptidase IV activities were concomitantly increased. The hypothalamic 5 hydroxyindole acetic acid levels were also increased. Changes in hormone secretion, peptidase activity and monoamine turnover had returned to baseline levels by 92 hr. Our results indicate that morphine withdrawal and the associated stress produce alterations in anterior pituitary thyrotropin and growth hormone secretion. Concomitant increases in hypothalamic prolyl endopeptidase and dipeptidyl peptidase activities may contribute to these changes.

Effect of modified brain histamine contents on prolactin and thyrotropin secretion in male rats

Effects of modified brain histamine contents on thyrotropin and prolactin secretion were studied in male rats. Under basal conditions the histamine content in the hypothalamus was approximately 8-10-fold higher than that in the striatum and the rest of the brain. L-histidine (1000 mg/kg, ip), a histamine precursor, and metoprine (20 mg/kg, ip), an inhibitor of histamine methyltransferase, elevated histamine content in the brain by 65% and 167%, respectively. When the treatments were given together an additive effect (119-250% increase) on brain histamine was observed. Metoprine significantly decreased serum prolactin levels, while L-histidine had no effect. This effect of metoprine was not modified by treatment with L-histidine. Thus, metoprine has an inhibitory effect on prolactin secretion that is not related to elevated brain histamine contents. The increased brain histamine content after L-histidine treatment had no effect on prolactin secretion. Basal levels of serum thyrotropin were decreased by both L-histidine and metoprine, L-histidine being more potent. In rats treated with alpha-fluoromethylhistidine, an inhibitor of L-histidine decarboxylase, the cold-induced (rats kept for 60 min at +4 degrees C) thyrotropin secretion was increased while the stress-induced prolactin secretion was decreased. In these rats, metoprine did not affect thyrotropin release but blunted the prolactin response. In conclusion, endogenous histamine inhibits thyrotropin secretion but does not affect prolactin release. Owing to its other effects, metoprine is not suitable as a tool to elevate endogenous histamine contents in the brain, at least when the regulation of anterior pituitary hormone release is being studied.

Differential disappearance of tolerance to thermal, hormonal and locomotor effects of morphine in the male rat

Development and disappearance of tolerance to various effects of morphine was studied by comparing the effect of acute morphine at 6 h and at 92 h after cessation of a 5-day regimen with increasing doses of morphine. After the 6-h lag time, tolerance manifested to the thermal, locomotor depressant and hormonal (stimulation of growth hormone and prolactin secretion) effects of morphine. The hypokinetic effect of morphine was replaced by a hyperkinetic effect and increased locomotor activity was evident following the challenge dose of morphine. Tolerance disappeared in different ways during the 92-h lag time. Tolerance persisted (hypothermic and hypokinetic effect) or disappeared considerably (prolactin secretion) during the 92-h withdrawal period. Tolerance to some effects also faded completely, and in contrast, even sensitization to various effects of morphine (growth hormone secretion, hyperthermic effect) could be seen after the 92-h withdrawal period. In addition, the original hypokinetic effect of morphine was replaced by a hyperkinetic effect (i.e., enhanced locomotor activity), which was even stronger after the 92-h lag time. The observed dissociation, which has not been seen to such an extent before, may be due to the differential modulation of the subtypes of mu-opioid receptors or differences in the adaptive mechanisms, e.g. conditioning, in various brain areas. Faster recovery of tolerance to an inhibitory than to a stimulatory effect of morphine during the withdrawal period may partially explain the sensitization to some effects of morphine.

Cold exposure attenuates effects of secretagogues on serum prolactin and growth hormone levels in male rats

The stimulatory effect of morphine, dexmedetomidine (an alpha 2-adrenoceptor agonist), 1-(3-chlorophenyl)-piperazine (m-CPP, a 5-HT1B agonist), U-50488H (a kappa-opioid receptor agonist), pimozide (a dopamine antagonist), and restraint stress on prolactin and growth hormone (GH) secretion was compared during cold exposure (4 degrees C) and under basal conditions (30 degrees C) in male rats. Rectal temperature was also measured. The stimulatory effect of morphine, dexmedetomidine, m-CPP, and partially U-50488H on prolactin secretion was attenuated in rats kept at 4 degrees C. Cold exposure did not abolish prolactin release induced by pimozide and restraint stress. Cold exposure also antagonized the effect of morphine and dexmedetomidine on GH secretion. The stimulatory effect of morphine on prolactin and GH secretion was restored in the warm environment despite the sustained hypothermia. Cold exposure blocked the stimulatory effect of morphine on prolactin secretion in rats that were tolerant to the hypothermic effect of morphine. Thus hypothermia caused by morphine, dexmedetomidine, and m-CPP during cold exposure is not the sole factor in the antagonistic effect of cold. We suggest that cold exposure releases some compound(s) modulating hypothalamic neural pathways.

N-nitro-L-arginine attenuates development of tolerance to antinociceptive but not to hormonal effects of morphine

The effect of N-nitro-L-arginine methyl ester on thyrotropin (TSH), growth hormone (GH) and prolactin levels in serum was studied after a single dose in male rats. The effect of repeated N-nitro-L-arginine methyl ester on the development of tolerance to the multiple effects of morphine was also examined. N-Nitro-L-arginine methyl ester (25 mg/kg i.p.) decreased cold-stimulated (rats were kept 30 min at +4 degrees C) TSH levels but did not alter basal TSH, GH or prolactin levels. Acute or repeated N-nitro-L-arginine methyl ester treatments were not antinociceptive alone, neither did they modify the effect of acute morphine. A 5-day treatment with increasing doses of morphine induced antinociceptive tolerance. This was attenuated by N-nitro-L-arginine methyl ester co-administration on the 3rd day, less so on the 5th day. Repeated morphine produced tolerance to the effect on TSH (decrease) and prolactin (increase) levels, but sensitization to the GH-elevating effect, measured after a 4-day delay. A 5-day treatment with N-nitro-L-arginine methyl ester did not modify the development of tolerance to the hormonal effects of morphine. In the case of TSH, it is difficult to draw a conclusion because the 5-day N-nitro-L-arginine methyl ester and morphine treatment generally decreased basal TSH levels. Sensitization to the hyperthermic effect of morphine occurred after a 4-day delay and this was not altered by N-nitro-L-arginine methyl ester. These results suggest that both nitric oxide-dependent and independent mechanisms are involved in the development of tolerance to the various effects of morphine.

Variation in tolerance to the antinociceptive, hormonal and thermal effects of morphine after a 5-day pre-treatment of male rats with increasing doses of morphine

The manifestation of tolerance to the effects of morphine on nociception and the secretion of anterior pituitary hormones, and the correlation of hormonal effects to changes in body temperature and to hypothalamic monoamines were studied in male rats. Morphine (three times a day in increasing doses) or saline (control) were administered intraperitoneally during a 5-day treatment and either saline or morphine was administered as an acute challenge 92 h later. The influence of the thermal environment on the effect of morphine on the body temperature was also studied. The 5-day morphine regimen was sufficient for the development of tolerance to the antinociceptive effect of morphine. After a 92-h lag-time, the tolerance was still complete. Tolerance to the depressant effect of morphine (10-25 mg/kg) on cold-stimulated TSH secretion was seen at 2 h, but was only barely detectable at 1 h, after the injection of a challenge dose. On the other hand, a tolerance to the stimulatory effect of morphine on prolactin secretion was already seen 1 h after the acute dose of morphine. Tolerance to the hypothermic effect of morphine (25 mg/kg) was evident in rats kept at +4 degrees C after the challenge dose. On the contrary, no tolerance to the hyperthermic effect of morphine (15 or 25 mg/kg) was observed in rats kept at +30 degrees C. However, the hyperthermia was reversed when these rats were moved to +4 degrees C for 30 min, irrespective of whether they were morphine pretreated or not. Thus the removal of the hyperthermic stimulus decreased the core temperature of all rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous histamine in cultured bovine adrenal chromaffin cells

Histamine releases catecholamines and opioids in primary cultured bovine adrenal medullary (BAM) chromaffin cells. We have studied whether histamine is synthesized and localized in BAM cells, and whether it can be released upon activation with secretagogues. In BAM cells histamine is immunohistochemically co-localized with tyrosine hydroxylase in 45 +/- 8% of all cells. Only histamine immunoreactivity was observed in 8 +/- 2% of all BAM cells. No mast-cell-like cells were observed in our system. Histamine can be released from BAM cells by high potassium (56 mM K+) in a calcium-dependent manner. Compound 48/80 did not release histamine from BAM cells but nicotine caused a dose-dependent liberation of the amine. Cultured BAM cells have histidine decarboxylase activity which is inhibited by alpha-fluoromethylhistidine. These results indicate that endogenous histamine is synthesized, stored and released in BAM chromaffin cells in vitro.

Effects of intraventricular taurine, homotaurine and GABA on serum prolactin and thyrotropin levels in female and in male rats

Serum prolactin and thyrotropin levels of conscious, unrestrained male and female rats were compared after intracerebroventricular (i.c.v.) administration of taurine, gamma-aminobutyric acid (GABA) and homotaurine. The amino acids studied had no clear effect on serum basal thyrotropin levels in male or female rats. All amino acids elevated serum prolactin levels in female rats at the dose of 5 mumol/rat; homotaurine by about 18-fold, taurine and GABA by 3-fold. Only homotaurine elevated serum prolactin of male rats at this dose, but its effect was less pronounced (p < 0.01) in male than in female rats. Although homotaurine was clearly more potent than the two other amino acids, at the dose of 10 mumol/rat taurine and GABA also elevated serum prolactin in male rats. These findings show that there are gender-related differences in the responses of serum prolactin levels to homotaurine, taurine and GABA in rats. The tuberoinfundibular dopaminergic pathway, which exerts tonic inhibitory influence on prolactin secretion, is sexually differentiated. Hence the gender-related differences in the effects of the amino acids on prolactin secretion suggest that they might inhibit dopamine release from the median eminence. In case of homotaurine, the gender effect was most pronounced. The less clear dependence of GABA's effect on the gender is in accordance with the suggestions that GABA influences the secretion of serum prolactin by more than one mechanism.