Increase of opioid mu-receptor gene expression in streptozotocin-induced diabetic rats

Opioids play an important role in the regulation of glucose homeostasis. In the previous report, we showed that activation of opioid mu-receptors produced a plasma glucose lowering effect in diabetic rats lacking insulin. In the present study, we found that the response of opioid mu-receptor is more sensitive in streptozotocin-induced diabetic rats (STZ-diabetic rats) than in normal rats. Intravenous injection of loperamide, an agonist of opioid mu-receptors, induced a dose-dependent decrease of plasma glucose from 3 microg/kg to 60 microg/kg in fasting STZ-diabetic rats. However, loperamide decreased the plasma glucose of normal fasting rats at the doses of 0.3 mg/kg to 1.5 mg/kg, which were much higher than those needed to produce the same effect in diabetic rats. The plasma glucose-lowering action of loperamide at the dose effective in normal rats disappeared in opioid mu-receptor knockout mice, while the plasma glucose-lowering response to loperamide was still observed in wild-type mice. This opens the possibility of mediation through opioid mu-receptor in the plasma glucose-lowering action of loperamide. Moreover, the mRNA level of opioid mu-receptor in the liver markedly increased in STZ-diabetic rats compared to normal rats. Normalization of plasma glucose concentrations in STZ-diabetic rats with exogenous insulin or phlorizin reversed mRNA and protein levels of opioid mu-receptor in the liver after 4 days of treatment. This shows that correction of hyperglycemia in STZ-diabetic rats may reverse the higher gene expression of opioid mu-receptor. These results suggest that hyperglycemia is responsible for increase of opioid mu-receptor in STZ-diabetic rats.

Loss of plasma glucose lowering response to cold stress in opioid mu-receptor knock-out diabetic mice

Opioid mu-receptor plays an important role in the regulation of glucose homeostasis in diabetic rats lacking insulin. Opioid mu-receptor knockout mice were employed to identify the essential role of this receptor in the present study. Western blotting analysis characterized the deletion of opioid mu-receptor in liver of knockout mice as compared to that of normal (wild-type) mice. We found that the plasma glucose concentration of diabetic mice induced by intraperitoneal injection of streptozotocin was markedly decreased after exposure to cold-stress in a cold room for 1 h. However, this plasma glucose lowering response to cold-stress was disappeared in diabetic mice lacking opioid mu-receptor. The important role of opioid mu-receptor in the plasma glucose lowering response to cold stress can thus be considered. Moreover, bilateral adrenalectomy abolished this plasma glucose lowering response to cold stress in diabetic mice with opioid mu-receptor, as compared to the shamed-operated animals. Therefore, activation of opioid mu-receptor by opioid from adrenal gland appears to be responsible for the plasma glucose lowering response to cold-stress in diabetic mice with insulin deficiency.

Release of beta-endorphin by prostaglandin E2 to lower plasma glucose in streptozotocin-induced diabetic rats

In the present study, Wistar rats, which received a streptozotocin injection to induce diabetes (STZ-diabetic rats), a model similar to insulin-dependent diabetes mellitus (IDDM) or type 1 diabetes mellitus, were used to investigate the effect of prostaglandin (PG) E2 on plasma glucose. Intravenous injection of PGE2 produced a dose-dependent lowering of plasma glucose level in fasting STZ-diabetic rats after 60 min. In addition to the blockade of this hypoglycemic effect by guanethidine (a noradrenergic nerve terminal-blocking agent), prazosin at a dose effective to block alpha1-adrenoceptors abolished the action of PGE2. An increase of plasma norepinephrine (NE) was also observed in STZ-diabetic rats receiving PGE2 injections. Participation of sympathetic stimulation by PGE2 may thus be speculated. Also, the plasma glucose-lowering effect of PGE2 was also blocked by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptor. Injection of PGE2 increased plasma beta-endorphin-like immunoreactivity (BER) in STZ-diabetic rats, and this action was abolished by prazosin. Bilateral adrenalectomy resulted in the loss of this PGE2 effect, and no increase was seen in plasma BER with PGE2 in STZ-diabetic rats. Therefore, beta-endorphin from the adrenal gland appears to be responsible for the lowering of plasma glucose in STZ-diabetic rats by PGE2 through an increase of NE release to activate alpha1-adrenoceptors.

Stimulatory effect of isoferulic acid on alpha1A-adrenoceptor to increase glucose uptake into cultured myoblast C2C12 cell of mice

In an attempt to elucidate the effect of isoferulic acid on alpha1-adrenoceptor (AR), the myoblast C2C12 cells of mice were employed to investigate the change of glucose uptake in the present study. Isoferulic acid enhanced the uptake of radioactive glucose into C2C12 cells in a concentration-dependent manner, which were abolished by pretreatment with prazosin. Effect of isoferulic acid on alpha1-AR was further characterized using the displacement of [3H]YM617 binding in C2C12 cells. The radioactive glucose uptake increasing action of isoferulic acid was abolished by tamsulosin or WB 4101 at concentration sufficient to block alpha1A-adrenoceptor (alpha1A-AR) but it was not modified by chlorethylclonidine (CEC) at the concentration sufficient to abolish alpha1B-AR. An activation of alpha1A-AR by isoferulic acid in C2C12 cells can thus be considered. Pharmacological inhibition of phospholipase C (PLC) by U73312 resulted in a concentration-dependent reduction of isoferulic acid-stimulated glucose uptake in C2C12 cells. This inhibition by U73112 was specific because the inactive congener, U73343, failed to modify the action of isoferulic acid. Also, chelerythrine and GF 109203X diminished the action of isoferulic acid at concentration sufficient to inhibit the activity of protein kinase C (PKC). The obtained data suggest that an activation of alpha1A-AR by isoferulic acid may increase the glucose uptake via PLC-PKC pathway in C2C12 cells.

Modest overexpression of neuropeptide Y in the brain leads to obesity after high-sucrose feeding

Neuropeptide Y (NPY), one of the most abundant peptide transmitters in the mammalian brain, is assumed to play an important role in feeding and body weight regulation. However, there is little genetic evidence that overexpression or knockout of the NPY gene leads to altered body weight regulation. Previously, we developed NPY-overexpressing mice by using the Thy-1 promoter, which restricts NPY expression strictly within neurons in the central nervous system, but we failed to observe the obese phenotype in the heterozygote. Here we report that in the homozygous mice, overexpression of NPY leads to an obese phenotype, but only after appropriate dietary exposure. NPY-overexpressing mice exhibited significantly increased body weight gain with transiently increased food intake after 50% sucrose--loaded diet, and later they developed hyperglycemia and hyperinsulinemia without altered glucose excursion during 1 year of our observation period.

Stimulatory effect of D-ephedrine on beta3-adrenoceptors in adipose tissue of rats

The effect of ephedrine on beta3-adrenoceptos (beta3-AR) was studied in the isolated adipose tissue of Wistar rat. Incubation with D-ephedrine (0.1-10 microM) induced a concentration-dependent decrease of uptake of [14C]-deoxy-D-glucose into white adipose tissues (WAT). The inhibitory effect of D-ephedrine was potentiated by BRL 37344, the agonist of beta3-AR and concentration-dependently inhibited by SR 59230A, the selective antagonist of beta3-AR. The action of D-ephedrine on beta3-AR was further blocked by the antibodies for beta3-AR, but not the immunoglobulin. in a concentration-dependent manner. Moreover, D-ephedrine increased glycerol release from the isolated brown adipose tissues (BAT) and this action was also abolished by SR 59230A at concentration sufficient to block beta3-AR. Thus, these results suggest that D-ephedrine has the ability to activate beta3-AR both in WAT and BAT of Wistar rats in vitro.

Changes in endogenous monoamines in aged rats

1. It has been documented that ageing may alter endogenous neurotransmitters. However, these results are controversial. Thus, in the present study, cerebral cortex and plasma from male Wistar rats aged 8 weeks and 6, 12 or 24 months were used to investigate the changes in monoamines using electrochemical detection. 2. A marked decrease in L-dihydroxyphenylalanine (L-DOPA) was observed in aged rats. Like the decrease in dopamine (DA), levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-HIAA), the major metabolite of 5-HT, in aged rats were decreased in the cerebral cortex and plasma. Plasma levels of noradrenaline and levels of adrenaline in the cerebral cortex were also decreased in aged rats. Moreover, levels of 3,4-dihydroxyphenylacetic acid (DOPAC), a metabolite of DA, in the cerebral cortex and plasma were reduced by ageing. The level of homovanillic acid (HVA) in all samples was markedly increased with ageing. 3. The ratio of DOPAC/DA and 5-HIAA/5-HT, being closely linked with the activity of monoamine oxidase, was increased in the cerebral cortex and plasma with ageing. The ratio of HVA/DOPAC, an index of the activity of catechol-O-methyltransferase, was also higher in the cerebral cortex and plasma of aged rats. 4. These data suggest that ageing may alter endogenous monoamines in both the brain and peripheral tissues.

Decrease of muscarinic M2 cholinoceptor gene expression in the heart of aged rat

It is well known that the baroreflex activity decreases with aging. However, the mechanisms of this change are still not clear. Thus, we investigated one of the parameters to see whether aging alters gene expression of muscarinic receptors in the heart of Wistar rat aged between 2 months (adult) and 24 months (aged). The mRNA level determination by Northern blot analysis for muscarinic M2 cholinoceptors in aged rat was decreased as compared to that in 2-month-old rats. Quantification of receptor protein using selective antibodies indicated that the level of muscarinic M2 cholinoceptor in the heart of 24-month-old rats was lower than that in 2-month-old animals. These results indicate the decrease of muscarinic M2 cholinoceptor in heart with aging that may contribute as one of the parameters for dysfunction in baroreflex activity.

Characterization of adenosine A1 receptor in cultured myoblast C2C12 cells of mice

In an attempt to investigate the presence of adenosine A1 receptor in cell line, we used N6-cyclopentyladenosine (CPA), an agonist of adenosine A1 receptor, to incubate with C2C12 cells in vitro. CPA increased the uptake of radioactive glucose into C2C12 cells in a concentration-dependent manner and this action was abolished by the antagonists, both 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (1,3-dipropy1-8-cyclopentylxanthine) and 8-(p-sulfophenyl)theophylline (8-SPT), at concentrations sufficient to block adenosine A1 receptor. Northern blot analysis showed the expression of adenosine A1 receptor mRNA by C2C12 cells. Western blotting also indicated a positive correlation (r = 0.99) of antibody recognized adenosine A1 receptor with membrane protein. The presence of adenosine A1 receptor in C2C12 cells can thus be considered. In the presence of U73312 (1-[6[[(17 beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H- pyrrole-2,5-dione), the specific inhibitor of phospholipase C, glucose uptake stimulated by CPA into C2C12 cells was reduced concentration-dependently while it was not modified by U73343 (1-[6[[(17 beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-2,5- pyrrolidinedione), the negative control of U73312. Moreover, chelerythrine and GF 109203X (3-[1-[3-(dimethylamino)propyl]-1H-indol-3-yl]-4-(1H-indol-3- yl)-1H-pyrrole-2,5-dione) also diminished the CPA-stimulated glucose uptake at concentrations sufficient to inhibit protein kinase C. The obtained data suggest that activation of adenosine A1 receptor in C2C12 cells may increase the glucose uptake via phospholipase C-protein kinase C pathway.

Synergistic cytotoxicity of Rana catesbeiana ribonuclease and IFN-gamma on hepatoma cells

RC-RNase purified from Rana catesbeiana (bullfrog) oocytes is a pyrimidine-guanine sequence-specific ribonuclease. RC-RNase is derived from the RNase superfamily genes exerting distinct ribonucleolytic activity and possesses cytotoxicity to tumor cells, but rarely to primary cells. In this study, we utilized RC-RNase to function with antiproliferative cytokines. The combination with TNF-alpha or TNF-beta would not aggravate cell death. However, the combination with IFN-gamma could induce synergistic cytotoxicity verified by XTT assays toward three hepatoma cell lines bearing different differentiation stages. The distinct cytotoxicity from RC-RNase or RC-RNase/IFN-gamma on different hepatoma cells was correlated with the differentiation extent but not the proliferation rate of the cells. Despite the synergistic cytotoxicity and severe mitochondrial disruptions in the RC-RNase/IFN-gamma-treated cells, we scarcely detected any significant feature of apoptosis or necrosis by FACS analysis on annexin-V/propidium iodide staining. The mechanisms of cell death triggered by RC-RNase or RC-RNase/IFN-gamma require further investigation.

Stimulation of insulin release in rats by Die-Huang-Wan, a herbal mixture used in Chinese traditional medicine

Die-Huang-Wan is a herbal mixture widely used in Chinese traditional medicine to treat diabetic disorders. We have investigated the effect of Die-Huang-Wan on plasma glucose concentration in-vivo. Die-Huang-Wan was administered orally (5.0, 15.0 or 26.0 mg kg(-1)) to three rat models. Wistar rats were used as the normal animal model, rats with insulin-resistance (induced by the repeated thrice daily injection of human long-acting insulin) were used as the non-insulin-dependent diabetic model, and streptozotocin-induced diabetic rats were used as the insulin-dependent diabetic model. In normal rats, approximately 1 h after oral administration of Die-Huang-Wan the plasma glucose concentration decreased significantly in a dose-dependent manner, from 5 to 26.0 mg kg(-1). A similar effect was observed in rats with insulin-resistance. However, this effect was not observed in streptozotocin-induced diabetic rats, even at an oral dose of 26.0 mg kg(-1). These results suggested an insulin-dependent action, a view supported by the increase of plasma insulin-like immunoreactivity in normal rats receiving Die-Huang-Wan. The results indicated that Die-Huang-Wan had an ability to stimulate the secretion of insulin and this preparation seemed helpful in improving the diabetic condition, especially hyperglycaemia in type-II diabetes.

Decrease of hypothalamic neuropeptide Y gene expression by vanadyl sulfate in streptozotocin-induced diabetic rats

In an attempt to elucidate the effect of vanadium compounds on the gene expression of neuropeptide Y (NPY), vanadyl sulfate (VOSO4) was orally administrated at the dose of 1 mg/kg body weight into streptozotocin-induced diabetic rats (STZ-diabetic rats) three times daily for 1 week. We found a marked lowering of plasma glucose with a significant decrease of food and water intake in these STZ-diabetic rats treated with VOSO4, although the weight gain was unaffected. The increase of hypothalamic NPY, both the mRNA level and peptide concentration, in STZ-diabetic rats was also reduced by this oral treatment of VOSO4. However, similar treatment of VOSO4 in normal rats failed to modify the feeding behavior and hypothalamic NPY gene expression. These data suggest that decrease of hypothalamic NPY gene expression by VOSO4 is related to the recovery of hyperphagia in diabetic rats lacking insulin.

Insulin restores neuronal nitric oxide synthase expression in streptozotocin-induced diabetic rats

Nitric oxide (NO) is known to play an important role in the pathophysiology of insulin-dependent diabetic mellitus (IDDM). In an attempt to investigate the relation between insulin and NO in IDDM, the present study employed male Wistar rats to induce IDDM by intravenous injection of streptozotocin (STZ). Four groups of rats were used; untreated normal control group, insulin treated STZ group, vehicle-treated STZ control, and one group of age-matched rats which were orally supplied with glucose to increase plasma glucose (glucose-challenged rats). Changes of the activity and gene expression of neuronal nitric oxide synthase (nNOS) were examined in cerebellum and kidney of these groups. The activity of nNOS in cerebellum, determined by conversion of [3H] L-arginine to [3H] L-citrulline, in STZ-induced diabetic rats was markedly lower than normal rats. Insulin treatment reversed the nNOS activity. Similar reversion by insulin treatment was also obtained in the gene expression of nNOS. However, the activity and gene expression of nNOS in glucose-challenged rats were not different from those in normal rats. The role of hyperglycemia can thus be ruled out. These findings indicated that an impairment of nNOS in the brain of rats with IDDM is mainly due to the absence of insulin.

Stimulatory effect of trans-cinnamaldehyde on norepinephrine secretion in cultured pheochromocytoma (PC-12) cells

AIM

The effect of trans-cinnamaldehyde (CNMA) on the release of norepinephrine (NE) from nerve terminal was investigated using rat pheochromocytoma 12 (PC-12) cells.

METHODS

The amount of NA released from PC-12 cells incubated with CNMA or related substances was quantified by high performance liquid chromatography (HPLC)-electrochemical detection. The lipophilic anion bisoxonol was used to monitor the effect of CNMA on the membrane potential.

RESULTS

CNMA stimulated the secretion of NE in a concentration-dependent manner from 5 mumol/L to 50 mumol/L, while the value of lactate dehydrogenase in the incubated medium was not influenced by CNMA. However, acetaldehyde, cinnamic acid, cinnamoyl chloride and cinnamamide failed to produce similar effect. The action of CNMA can thus be considered specific. The depolarizing effect of CNMA on the membrane potential was also illustrated by a concentration-dependent increase in the fluorescence of bisoxonol, a potential-sensitive dye. Saxitoxin attenuated the depolarizing action of CNMA at concentrations sufficient to block sodium channels. Besides, the effect of CNMA to depolarize the membrane potential in PC-12 cells is greater than that of 4-aminopyridine (4-AP). The action of CNMA on NE releasing depends on extracellular Ca2+ and is attenuated by 8-bromo-cAMP at concentrations sufficient to inhibit the action of cyclic AMP.

CONCLUSION

These findings suggest that CNMA can depolarize the membrane to result in a Ca(2+)-dependent and cyclic AMP-related release of NE from PC-12 cells.

Effects of trilinolein on superoxide dismutase activity and mrna levels in aortic smooth muscle cells

1. Atherosclerotic cardiovascular disease is still the leading cause of death in Western countries. Oxygen free radicals are considered to be intimately involved in the development of atherosclerosis. Anti-oxidants may help to protect mammalian cells from the damage induced by these reactive oxygen species. Many reports have indicated that anti-oxidants used in the treatment or prevention of disease could modify the levels of superoxide dismutase (SOD). However, the effects of long-term anti-oxidant treatment on the levels of SOD in smooth muscle cells (SMC) is still unclear. In the present study, the effects of the lipophilic anti-oxidant trilinolein on the activity and gene expression of SOD in SMC were evaluated. 2. After 2 days incubation with 0.1 micromol/L trilinolein, the activity and mRNA levels of SOD were increased in rat aortic SMC (A7r5), but there was no significant change in these parameters with a higher concentration of 1 micromol/L trilinolein. 3. In contrast, after 7 days incubation with trilinolein, both the activity and mRNA levels of SOD were lowered in a dose-dependent manner. 4. These data emphasize the importance of choosing an optimal dosage for supplementation with anti-oxidants in humans for the scavenging of oxygen free radicals.

Gene expression of alpha(1A)-adrenoceptor but not alpha(1B)-adrenoceptor in cultured myoblast C(2)C(12) cells of mice

Subtypes of alpha(1)-adrenoceptor (alpha(1)-AR) in the cultured myoblast C(2)C(12) cells have been examined using molecular biological identifications. Expression of the two distinct mRNAs that encode proteins of alpha(1A)- and alpha(1B)-AR was studied using reverse transcription combined with polymerase chain reaction (RT-PCR). Results of RT-PCR demonstrated a marked expression of alpha(1A)-AR in the prostate of rats. Samples from the C(2)C(12) cells under the same amount of amplification showed the expression of alpha(1A)-AR at a level slightly lower than that from the prostate of rats. Western blotting analysis using receptor subtype-specific antibody also indicated that the alpha(1A)-AR was expressed in C(2)C(12) cells as well as in prostate of rats. However, although the expression of alpha(1B)-AR was obtained in the spleen of rats, expression of alpha(1B)-AR was undetectable in the C(2)C(12) cells either the results of RT-PCR or the Western blotting analysis. The present study suggests that alpha(1A)-AR is a major subtype of alpha(1)-AR in the C(2)C(12) cell line.

Role of alpha1A-adrenoceptor in the regulation of glucose uptake into white adipocyte of rats in vitro

In an attempt to know the functional role of alpha1A-adrenoceptors in adipose tissue, white adipocytes (WAT) of Wistar rats were used to investigate the change of glucose uptake after pharmacological activation of alpha1-adrenoceptors. Methoxamine enhanced the uptake of radioactive glucose into isolated WAT in a concentration-dependent manner. Translocation of glucose transporter (GLUT4) from cytosol to membrane was also stimulated with methoxamine. Action of methoxamine to raise glucose uptake was abolished in WAT pre-incubated with the antagonists, both tamsulosin and WB 4101, at concentrations sufficient to block alpha1A-adrenoceptors. However, chlorethylclonidine (CEC). the antagonist of alpha1B-adrenoceptors, showed the inhibition of methoxamine-induced action only at a higher concentration. Even under the treatment with maximal concentration of CEC, methoxamine can produce action about 80% of the vehicle-treated control. The major role of alpha1A-adrenoceptors in the stimulation of glucose uptake by methoxamine can thus be considered. In the presence of specific inhibitor of phospholipase C (PLC), U73312, methoxamine-stimulated glucose uptake into WAT was reduced in a concentration-dependent manner and U73343, the negative control of U73312, did not affect the action of methoxamine. Moreover, chelerythrine and GF 109203X diminished the methoxamine-stimulated glucose uptake at a concentration sufficient to inhibit protein kinase C (PKC). Inhibition of phosphoinositide-3 kinase (PI-3 kinase) by LY294002 also abolished methoxamine-stimulated glucose uptake. Therefore. the obtained data suggest that an activation of alpha1A-adrenoceptors, presence in WAT, by agonist and/or neurotransmitter may increase the glucose uptake via PLC-PKC pathway and the activation of PI-3 kinase.

Activation of adenosine A1 receptors by drugs to lower plasma glucose in streptozotocin-induced diabetic rats

To examine the role of the adenosine A1 receptor in glucose regulation in the absence of insulin, the present study investigated the changes of plasma glucose in male streptozotocin-induced diabetic rats (STZ-diabetic rats) using dipyridamole to increase endogenous adenosine and N6-cyclopentyladenosine (CPA) to activate the adenosine A1 receptor. Intravenous injections of dipyridamole or CPA induced a dose-dependent decrease of plasma glucose in fasting STZ-diabetic rats. Plasma glucose lowering action of dipyridamole, like that of CPA, was inhibited in a dose-dependent manner by pre-treatment with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) or 8-(p-sulfophenyl)theophylline (8-SPT) at which block the adenosine A1 receptors. Action of the adenosine A1 receptors can thus be considered. In isolated skeletal muscle, CPA enhanced the glucose uptake in a concentration-dependent manner. Blockade of this action by DPCPX and 8-SPT again supported the mediation of the adenosine A1 receptor. Also, CPA produced an increase of glycogen synthesis in isolated soleus muscle. Moreover, CPA decreased plasma triglyceride and cholesterol levels significantly in STZ-diabetic rats. These results suggest that activation of adenosine A1 receptors can increase glucose utilization in peripheral tissues by increasing tissue uptake and glycogen synthesis to lower plasma glucose in rats lacking insulin.

A double-blind placebo-controlled study of the effectiveness and tolerability of oral stevioside in human hypertension

AIMS

Stevioside is a natural plant glycoside isolated from the plant Stevia rebaudiana which has been commercialized as a sweetener in Japan for more than 20 years. Previous animal studies have shown that stevioside has an antihypertensive effect. This study was to designed to evaluate the effect of stevioside in human hypertension.

METHODS

A multicentre, randomized, double-blind, placebo-controlled study was undertaken. This study group consisted of 106 Chinese hypertensive subjects with diastolic blood pressure between 95 and 110 mmHg and ages ranging from 28 to 75 years with 60 subjects (men 34, women 26; mean +/- s.d., 54.1+/-3.8 years) allocated to active treatment and 46 (men 19, women 27; mean +/- s.d., 53.7+/-4.1 years) to placebo treatment. Each subject was given capsules containing stevioside (250 mg) or placebo thrice daily and followed-up at monthly intervals for 1 year.

RESULTS

After 3 months, the systolic and diastolic blood pressure of the stevioside group decreased significantly (systolic: 166.0+/-9.4-152.6+/-6.8 mmHg; diastolic: 104.7 +/- 5.2-90.3+/-3.6 mmHg, P<0.05), and the effect persisted during the whole year. Blood biochemistry parameters including lipid and glucose showed no significant changes. No significant adverse effect was observed and quality of life assessment showed no deterioration.

CONCLUSIONS

This study shows that oral stevioside is a well tolerated and effective modality that may be considered as an alternative or supplementary therapy for patients with hypertension.

Effect of N-(biphenylyl-methyl)imidazole, a type 1 angiotensin II receptor inhibitor, on the contractile function of the rat corpus cavernosum

The effect of N-(biphenylyl-methyl)imidazole, losartan potassium, a newly developed antihypertensive type 1 angiotensin II receptor antagonist on the rat erectile function, was studied. Sexually active 9-week-old male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were given losartan 60 mg/kg intraperitoneal injections. Mean blood pressure (MBP) dropped significantly in both SHR and WKY rats (for SHR: from 140 +/- 8 to 114 +/- 5 mm Hg, p < 0.05, n = 8; for WKY: from 113 +/- 7 to 79 +/- 9 mm Hg, p < 0.05, n = 8). On the contrary, the intracavernous pressure (ICP) of SHR and WKY rats did not differ significantly from that of the corresponding controls receiving saline injections (p > 0.05, n = 8 for each group). For the chronic study, the rats were fed with losartan 30 mg/kg/day for 30 days. MBP decreased significantly in SHR but not in WKY rats (for SHR: from 137 +/- 7 to 113 +/- 5 mm Hg, p < 0.05, n = 8; for WKY: from 110 +/- 6 to 107 +/- 5 mm Hg, p > 0.05, n = 8). The ICP of the losartan-treated rats was not significantly different from that of control rats (p > 0.05, n = 8 for each group). In contrast, WKY rats receiving guanethidine 1 mg/kg/day for 30 days showed significantly decreased ICP. Angiotensin II (10(-9)-10(-5) M) and losartan (10(-9)- 10(-5) M) did not induce significant contractile responses of the cavernosal strip when tested in vitro. On the other hand, methoxamine 10(-4) M induced good contractile responses. In conclusion, the present study demonstrated that angiotensin II did not cause significant change in the contractile status of rat corpus cavernosum. Correspondingly, the type 1 angiotensin II inhibitor effectively lowered blood pressure but did not affect cavernosal contractile function, thus is useful clinically in the treatment of hypertensive disorders without significant detrimental effects on male sexual function.

Stimulatory effect of caffeic acid on alpha1A-adrenoceptors to increase glucose uptake into cultured C2C12 cells

In an attempt to understand the antihyperglycemic action of caffeic acid, the myoblast C2C12 cells were employed to investigate the glucose uptake in the present study. Caffeic acid enhanced the uptake of radioactive glucose into C2C12 cells in a concentration-dependent manner. Similar effect of phenylephrine on the uptake of radioactive glucose was also observed in C2C12 cells. Prazosin attenuated the action of caffeic acid in a way parallel to the blockade of phenylephrine. Effect of caffeic acid on alpha1-adrenoceptors was further supported by the displacement of [3H]prazosin binding in C2C12 cells. Moreover, the glucose uptake-increasing action of phenylephrine in C2C12 cells was inhibited by the antagonists of alpha1A-adrenoceptors, both tamsulosin and WB 4101, but not by the antagonist of alpha1B-adrenoceptors, chlorethylclonidine (CEC). The presence of alpha1A-adrenoceptors in C2C12 cells can thus be considered. Similar inhibition of the action of caffeic acid was also obtained in C2C12 cells co-incubating these antagonists. An activation of alpha1A-adrenoceptors seems responsible for the action of caffeic acid in C2C12 cells. In the presence of U73312, the specific inhibitor of phospholipase C, caffeic acid-stimulated uptake of radioactive glucose into C2C12 cells was reduced in a concentration-dependent manner and it was not affected by U73343, the negative control of U73312. Moreover, chelerythrine and GF 109203X diminished the action of caffeic acid at concentrations sufficient to inhibit protein kinase C. Therefore, the obtained data suggest that an activation of alpha1A-adrenoceptors in C2C12 cells by caffeic acid may increase the glucose uptake via phospholipase C-protein kinase C pathway.

Structure-activity relationships of anthraquinones in the decrease of intestinal motility

The effects of substituted anthraquinones on intestinal motility were evaluated in-vitro using rabbit small intestinal strips. This structure-activity relationship study revealed the critical requirement of a hydroxy group at R2 position. The intestinal motility was inhibited 50% (IC50) by emodine (8 microM), 2-hydroxy anthraquinone (20 microM), 2,6-dihydroxy anthraquinone (25 microM), 2,7-dihydroxy anthraquinone (10 microM), 1,2,4-trihydroxy anthraquinone (80 microM) and 1,2,5,8-tetra-hydroxyanthraquinone (9 microM). The presence of other polar groups at R2 position such as an amino, aldehyde and carboxylic acid group significantly reduced the activity (IC50 360-400 microM). The presence of a methyl group and esterification of the carboxylic acid at R2 position was found to abolish the activity. These data are useful for the future development of anthraquinones as laxative agents.

Alterations in beta-adrenergic receptor density and adenylate cyclase activity in the rat brain treated chronically with lead

Behavioral and memory impairment resulting from lead exposure is well known but the mechanism is not. We utilized the brain of lead exposed rats to investigate this problem. In an effort to elucidate the mechanism responsible for this alteration we examined blood and brain lead levels, brain beta-adrenoceptor density and cyclic AMP production in lead exposed rats. Wistar rats used in these trials were divided into six groups of ten animals each. Five groups were given drinking water containing 0.05, 0.1, 0.5, 1 and 2% lead acetate for a period of 60 days. One group (control group, 0% lead acetate) was given pure water. Application of a trend test indicated that both blood and brain lead levels increased significantly from group 0% to group 2% (group 0% <group 0.05% <group 0.1% <group 0. 5%<group 1%<group 2%), but that brain beta-adrenoceptor density and cyclic AMP levels stimulated by isoproterenol decreased (group 2%<group 1%<group 0.5%<group 0.1%<group 0.05%<group 0%). Kd did not vary among the six groups and this indicated that the affinity of the remaining beta-adrenoceptors for [125I]iodocyanopindolol was not changed. Linear regression analysis showed that beta-adrenoceptor density and stimulated cyclic AMP level in brain was found to be negatively correlated with brain lead level (P<0.001). The results show lead exposure that may be the result of an alteration of beta-adrenergic receptor and adenylate cyclase activity in brain.

Gastric mucosal damage induced by arecoline seizure in rats

In an attempt to know the relation of seizure and gastric mucosal damage, we challenged arecoline (ACL) centrally to induce seizure and investigated gastric hemorrhagic injury in acid-irrigated stomachs of rats. The protective effects of several drugs also were evaluated. After deprivation of food for 24 h, rats were received laparotomy under diethylether-anesthesia. Both pylorus sphincters and carotid esophagus were ligated. The forestomach was equipped with a cannula for gastric irrigation. After recovery from anesthesia (approximately 1 h), the stomach was irrigated for 2 h with an acid solution containing 100 mM HCl and 54 mM NaCl or the same volume of normal saline. Intracerebroventricular (i.c.v.) ACL (0, 1, 3 or 10 mg/kg dissolved in 10 microl of CSF) was challenged to rats immediately after gastric irrigation. The seizure in rats was produced by ACL in a dose-related manner. The ulcerogenic parameters such as decrease of gastric mucosal glutathione levels and increase of histamine concentrations and lipid peroxide generations as well as the raise of luminal hemoglobin contents and exacerbated mucosal lesions were obtained depending on the doses of ACL challenged. These ulcerogenic parameters produced in ACL (10 mg/kg, i.c.v.) seizure rats were markedly ameliorated by gastric vagotomy or central anticholinergics. Intraperitoneal ketotifen, zinc sulfate, diphenhydramine or cimetidine also produced significant (p<0.05) inhibitions of these ulcerogenic parameters in ACL seizure rats. In conclusion, central ACL seizure may produce gastric oxidative stress and hemorrhagic lesions via vagal nervous activation and histamine release in acid-irrigated stomachs of rats.

Changes in superoxide dismutase activity and mRNA in vivo after short-term supplementation with trilinolein in rats

BACKGROUND

Oxidative damage plays a central role in atherogenesis and antioxidation defense mechanisms may prevent atherosclerosis. This study evaluated the effect of short-term supplementation of the natural lipophilic antioxidant trilinolein on superoxide dismutase (SOD) activity and SOD-mRNA gene expression in vivo in rat vital organs.

METHODS

Male Wistar rats (n = 8) were injected intraperitoneally with trilinolein (1 mM/ml/kg/day in 0.5% ethanol) daily for three consecutive days. Two control groups (n = 8) were administered saline or 0.5% ethanol in saline, respectively, for three days.

RESULTS

Assay of SOD activity and SOD-mRNA by Northern blotting in rat liver, spleen and brain showed significant increases in SOD activity and increased SOD-mRNA gene expression.

CONCLUSIONS

The natural lipophilic antioxidant trilinolein potentiates the SOD antioxidation defense mechanism and increases gene expression of SOD-mRNA after short-term supplementation in rats.