Cardiovascular responses to NMDA injected into nuclei of hypothalamus or amygdala in conscious rats.

The nuclei of hypothalamus and amygdala have been shown to be involved in the central cardiovascular homeostasis. Recent studies suggest that glutamate-containing neurons have an important role in the regulation of the central cardiovascular function. In this study, we demonstrate the roles of the central nucleus of the amygdala and the paraventricular nucleus of the amygdala and the paraventricular nucleus or the dorsomedial nucleus of the hypothalamus in N-methyl-D-aspartate (NMDA) induced blood pressure and heart rate changes in conscious Sprague-Dawley rats. Intracerebroventricular or parenchymal injections of NMDA evoke increases in arterial pressure. The NMDA-induced elevations in blood pressure are more prominent when NMDA is administered into the dorsomedial nucleus of the hypothalamus. Microinjections of NMDA into the dorsomedial hypothalamus exert significant heart rate increases, whereas NMDA when administered into the paraventricular nucleus of the hypothalamus or into the central nucleus of the amygdala has no significant effect on the heart rate. The dorsomedial nucleus of the hypothalamus is found to be the most effective site in this respect. The present study provides strong evidence for the tonic glutamatergic influence on blood pressure and heart rate via NMDA receptors located within the dorsomedial nucleus and to a lesser extent via those located within the paraventricular nucleus of the hypothalamus.

Participation of NMDA and kainate receptors of paraventricular nucleus in cardiovascular responses to glutamate receptor agonist.

The nuclei of the hypothalamus have been shown to be involved in central cardiovascular homeostasis. Recent studies suggest that glutamate-containing neurons have an important role in the regulation of central cardiovascular function. We report first on the effects of intracerebrally injected NMDA and non-NMDA receptor ligands on blood pressure and heart rate in conscious Sprague-Dawley rats. In the second part, we describe the effect of blockade of NMDA or kainate receptors in the paraventricular nucleus on glutamate receptor agonist-induced blood pressure responses. Intracerebroventricular injections of L-glutamic acid, NMDA and kainic acid produced increases in mean arterial pressure. Kainic acid produced significant decreases in heart rate. Microinjection of DL-2-amino-5-phosphonopentanoic acid (APV; 25 and 50 nmol), a competitive NMDA receptor antagonist, into the paraventricular nucleus blunted the increases in the mean arterial pressure evoked by intracerebroventricular injections of NMDA (1 nmol), whereas microinjection of dinitroquinoxaline (DNQX; 20, 40 and 80 pmol), which acts as an antagonist at kainate receptors, failed to antagonize the cardiovascular effects of intracerebroventricular kainic acid (10 pmol). Microinjections of NMDA (100 pmol) into the paraventricular nucleus produced pressor responses, but kainic acid (5 and 10 pmol) failed to affect either mean arterial pressure or heart rate. These results suggest participation of the glutamergic system in cardiovascular regulation via NMDA receptors located within the paraventricular nucleus of the hypothalamus in rats.

The effect of tizanidine on maximal electroshock seizures (MES) in mice.

Tizanidine, an alpha-2 adrenergic agonist, is a centrally active muscle relaxant and a spasmolytic drug. The aim of our study was to investigate the activity of tizanidine on maximal electroshock seizures (MES) in mice. In the first part of the study, convulsive current 50 (CC 50) value to produce seizures was found. Then, tizanidine was given intraperitoneally (IP) at the doses of 0.5, 1, and 2 mg/kg, and orally (PO) at the doses of 5, 10, 20, 40 mg/kg. We found that tizanidine at the doses of 1 and 2 mg/kg IP and 40 mg/kg PO caused a significant protection against MES. In the second part of the study, after pretreatment with yohimbine, an alpha-2 adrenergic receptor blocker, at the dose of 2 mg/kg, anticonvulsant effect of tizanidine is diminished. We concluded that the mode of action of the anticonvulsant effect of tizanidine may be mediated by the central alpha-2 adrenergic receptors.

Tizanidine is an effective agent in the prevention of focal cerebral ischemia in rats: an experimental study.

BACKGROUND: Focal cerebral ischemia secondary to cerebral vessel occlusion is still an important cause of mortality and morbidity. Excitatory neurotransmitters are gathered in the extracellular space during ischemia and initiate or stimulate a series of pathophysiological biochemical processes and consequently lead to neuronal death. Tizanidine (Sandoz compound DS 103-282, 5-chloro4,2 (2-imidazolin-2-yl-amino)-2,1,3-benzothiazol hydrochloride) is a selective alpha 2 adrenoreceptor agonist which shows its effect by stimulating presynaptic alpha 2 adrenoreceptors in central ASPergic and GLUergic system by inhibiting aspartic acid and glutamic acid release. In this study, the effect of Tizanidine on reversible focal cerebral ischemia was evaluated. METHODS: Cerebral blood flow to the left hemisphere of adult Sprague-Dawley rats (n=48) was temporarily interrupted by middle cerebral artery and bilateral common carotid artery occlusion for 3 hours in eight rats of each group. Tizanidine was given to each group of rats intraperitoneally before the ischemic insult, 2 hours after ischemia, right after the reperfusion, 2 h after reperfusion, and 4 hours after reperfusion; the animals survived for 24 hours after the reperfusion. After killing and triphenyltetrasoliumchloride staining of brain slices, infarction volumes and ratios of the brains were calculated and the results were compared with those of the control group. RESULTS: Infarction volumes and infarction ratios of the Tizanidine group 1/2 hours before ischemia (143.7+/-6.34 mm3 and 10.1+/-0.43%) and the Tizanidine group 2 hours after ischemia (145.6+/-6.32 mm3 and 10.3+/-0.43%) were found to be significantly lower in favor of the Tizanidine groups when compared with those of the control group (173.9+/-6.38 mm3 and 12,4+/-0.41%). Tizanidine is not effective if used just after reperfusion or later. CONCLUSION: This study shows that Tizanidine pretreatment before the ischemic insult and the administration of the drug within the 2 hours after ischemia reduces ischemic damage significantly. Therefore, this drug can be used as a protective and therapeutic agent in ischemic diseases.

Alteration of cholinergic pressor and antinociceptive responses in rats pretreated with the cholinergic toxin AF64A.

1. In the present study, the pressor and antinociceptive effects of physostigmine and oxotremorine were investigated in rats injected with AF64A intracerebroventricularly. 2. Physostigmine (50-100 micrograms/kg, i.v.)-induced pressor responses were significantly lower in AF64A-injected rats compared with saline-injected animals, whereas oxotremorine (20-80 micrograms/kg, i.v.)-induced responses were found to be similar to those seen in the saline group. 3. The physostigmine (100 micrograms/kg, s.c.)-induced antinociceptive effect was totally abolished by AF64A treatment, but that of oxotremorine (30 micrograms/kg, s.c.) remained unchanged at the tail-flick test. 4. The results of this study present functional evidence for AF64A-produced substantial loss of cholinergic neurons involved in the regulation of blood pressure and nociception but not in postsynaptic muscarinic receptors.

Role of paraventricular and dorsomedial nuclei of the hypothalamus and central nucleus of the amygdala on muscimol-induced cardiovascular responses.

Gamma-aminobutyric acid (GABA) plays an important role in the central control of cardiovascular functions. Previous evidence indicates that a tonically active GABAergic system exists in forebrain structures. The purpose of this study was to examine the role of the unilateral lesion of the central nucleus of amygdala, paraventricular or dorsomedial nuclei of the hypothalamus on muscimol-induced cardiovascular responses. Electrolytic ablation of nuclei was made by a monopolar isolated electrode under a stereotaxic instrument, 3-5 days before the experiments. Effects of intracerebroventricular injections of muscimol were investigated in intact, lesioned and sham-lesioned rats. On the day of the experiments, blood pressure and heart rate recordings were carried out in male Sprague-Dawley conscious rats. Muscimol produced decreases in arterial blood pressure and heart rate. The hypotensive effect of muscimol was completely inhibited in rats with dorsomedial nucleus lesions, whereas the bradycardic effect was partially prevented. The results indicate that the dorsomedial nucleus of the hypothalamus plays an important role on muscimol-induced blood pressure and heart rate responses.

The role of amygdala and hypothalamus in GABAA antagonist bicuculline-induced cardiovascular responses in conscious rats.

gamma-Aminobutyric acid (GABA) is known to play an important role in the central control of cardiovascular functions. GABAergic agonists and antagonists elicit blood pressure and heart rate changes when injected into the brain. It was demonstrated here that bicuculline methiodide (BMI), a GABAA antagonist, caused dose-dependent increases in both blood pressure and heart rate in conscious rats when injected intracerebroventricularly. The roles of the central nucleus of the amygdala (CeA), the paraventricular nucleus (PVN) and the dorsomedial nucleus (DMH) of the hypothalamus in BMI-induced blood pressure and heart rate changes were investigated in this study. The pressor effect of BMI was significantly attenuated by the electrolytic ablation of DMH and PVN, whereas it was only slightly, but insignificantly reduced by CeA lesions. The microinjection of BMI into the DMH and the PVN elicited significant pressor and tachycardic responses whereas only a slight increase was observed in rats injected BMI into the CeA. The BMI-induced increases in both blood pressure and heart rate were more prominent when given into the DMH. These results indicate that the DMH plays an important role in GABAergic control of cardiovascular functions. The PVN and CeA seem to have a minor part in this respect.

Antinociceptive effect of D-aspartic acid in mice.

The effects of D- and L-aspartic acids on the nociceptive tail flick reflex in mice were investigated. D-Aspartic acid (115-230 mg/kg, IP) was found to increase tail flick latency significantly. Naloxone (0.1 mg/kg) abolished the analgesic effect of D-aspartic acid (115 mg/kg). Morphine and D-aspartic acid, when combined at their nonanalgesic doses, led to significant analgesia. It may be concluded that the opioid system is involved in the antinociceptive effect of D-aspartic acid. Both morphine and D-aspartic acid were previously reported to inhibit L-aspartic acid production via blockade of L-asparaginase. L-Aspartic acid, which was ineffective alone, significantly inhibited the antinociceptive effects of both D-aspartic acid and morphine.

The hypotensive effect of cisapride in rat.

1. Cisapride is a prokinetic agent believed to facilitate acetylcholine release from the myenteric plexus of the gut. The aim of the present study was to investigate the effect of cisapride on blood pressure and the effects of muscarinic receptor antagonists on the cisapride-induced blood pressure changes. 2. Cisapride was given i.v. alone or 10 min after muscarinic receptor antagonists. Cisapride given i.v. produced a significant decrease in blood pressure in a dose-related manner. Atropine, AF-DX 116 and 4-DAMP given 10 min before cisapride injection, partially inhibited the hypotensive response to cisapride. In pithed rat, the effect of cisapride on blood pressure remained unaltered. 3. This study indicates that the action of cisapride is not through central mechanisms and part of cisapride's effect is through the cholinergic system.

Effect of diltiazem on renal function in patients with liver cirrhosis.

Calcium channel blockers have strong vasodilator, natriuretic and diuretic actions in normal and hypertensive subjects. The aim of this study was to evaluate the effect of diltiazem on renal function, renin-angiotensin-aldosterone axis (RAA) and atrial natriuretic factor (ANF) in patients with liver cirrhosis. Seven patients (3 females and 4 males) with a mean age of 56.3 +/- 11.1 years (36-68) entered the trial. All of the patients had HBV (6 cases) or HCV (1 case) related Child A (3 cases) or Child B (4 cases) liver cirrhosis proven by liver biopsy. Patients were given placebo for 15 days followed by p.o. diltiazem 30 mg t.i.d. for 15 days. Urinary volume, natriuresis, creatinine clearance, plasma renin activity (PRA), ANF and aldosterone (ALD) levels were determined after the washout period and during the first and second weeks of drug treatment. Urinary volume increased by 25-170% in 5 cases but this difference did not reach statistical significance. Slight increases in natriuresis occurred in some cases on the 3rd day of the trial but the overall results were not statistically significant (191.50 +/- 26.85 vs 204.07 +/- 39.83 mmol/l). Diltiazem induced no significant changes in PRA, ALD and ANF levels or creatinine clearance during the first or second weeks of the trial. There was a significant drop in the pulse rate on the first or second weeks of the treatment (p less than 0.01 and p less than 0.05, respectively). No significant changes were noted on mean arterial pressure (MAP).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of chronic guanfacine administration on high plasma vasopressin levels in essential hypertension.

In the past several years, investigators have given evidence that vasopressin (VP), in addition to its antidiuretic function, may play an important role in cardiovascular regulation through other mechanisms. An increased plasma VP level has been reported in some patients with mild-to-moderate essential hypertension (EH). Additionally, yohimbine, a selective alpha 2-adrenoceptor antagonist, has been shown to increase the plasma VP level and blood pressure (BP) in man. The present study was performed to evaluate the effects of chronically administered guanfacine, a centrally acting alpha 2-adrenoceptor agonist, on high plasma VP levels in patients with mild-to-moderate EH in whom no other causes responsible for elevated plasma VP levels were present. The relations among VP, BP and renin-angiotensin-aldosterone system were also investigated. Eleven patients (8 women and 3 men aged 62 +/- 3 years) with untreated and uncomplicated EH were included in the study after a 2-week placebo period and kept on a diet containing 120 mmol sodium and 80 mmol potassium daily. In all patients treated once daily with 1 mg of guanfacine for 4 weeks, the drug-induced changes in plasma levels of VP and aldosterone (ALD), plasma renin activity (PRA), plasma osmolality, BP and heart rate were determined. A marked reduction in plasma VP levels (p less than 0.001) was observed and this was accompanied by a significant fall in mean arterial blood pressure (p less than 0.001). No significant changes in heart rate, plasma osmolality, PRA and plasma ALD levels were found. The results suggest that guanfacine might suppress VP secretion via alpha 2-adrenoceptors without significantly affecting renin-angiotensin-aldosterone system.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin release by D-aspartic acid, morphine and prolyl-leucyl-glycinamide (PLG) in DI Brattleboro rats.

The L-asparaginase activities of the brains of the Wistar, heterozygous and homozygous Brattleboro rats divided into three parts namely the anterior, middle and posterior which respectively contained cerebral cortex, hippocampus + midbrain + thalamus + hypothalamus cerebellum + pons + medulla oblongata were estimated. The L-asparaginase activities of all the three parts in the homozygous Brattleboro rats were significantly higher than in the Wistar rats as well as in the heterozygous Brattleboro rats. Twenty min following the injections of 200 mg/kg D-aspartic acid, 20 mg/kg morphine, 200 mg/kg D-aspartic acid + 20 mg/kg morphine, 6 mg/kg prolyl-leucyl-glycinamide (PLG) and 6 mg/kg PLG + 20 mg/kg morphine the L-asparaginase activities of all three parts of the homozygous Brattleboro rat brains were found to be significantly inhibited. After having seen the suppressive effect of the drugs and their combinations used before the homozygous Brattleboro rats were given D-aspartic acid, morphine, D-aspartic acid + morphine, PLG and PLG + morphine for seven days. Then their plasma vasopressin levels were determined by RIA. The treatments applied to the homozygous Brattleboro rats caused the appearance of a significant amount vasopressin in the plasma. The results were interpreted as evidence for the fact that the inhibition of the brain L-asparaginase provides and/or accelerates the biosynthesis and/or release of vasopressin. As morphine has a vasopressin releasing and a brain L-asparaginase inhibiting effect the antidiuretic action of morphine was considered to be linked to its inhibitory effect on the brain L-asparaginase.

Feeding, drinking, urine osmolality in DI Brattleboro rats: changes by morphine, naloxone, D-amino acids, prolyl-leucyl-glycinamide (PLG).

Brattleboro rats placed in metabolism cages were injected with morphine (Mor), naloxone (Nal), D- and L-aspartic acid (D- and L-Asp), D-phenylalanine (D-Phe), D-leucine (D-Leu) and prolyl-leucyl-glycinamide (PLG), alone and in suitable combinations. Food and fluid intake, urine outflow, faeces weight, rectal temperature and urinary osmolality were determined at the end of seven hours period of time. Mor, Nal, D-Asp and PLG alone caused a significant decrease in food and fluid intake, urine volume and faeces weight and a significant increase in urinary osmolality being the osmolality of the Mor, D-Asp and PLG injected groups higher than 300 mOsmol/kg. The combination of Nal with Mor, D-Asp and PLG appeared to intensify the changes induced by Mor, D-Asp and PLG whereas L-Asp antagonized the majority of changes caused by Mor or PLG. The results were discussed in the light of the previous experimental findings.

Effect of D- and/or L-aspartic acids on feeding, drinking, urine outflow and core temperature.

Rats were given D- and/or L-aspartic acids (Asp) in saccharin solution for one week. Body weight gain, daily food and fluid intake, weight of faeces, urine outflow and osmolality, and rectal temperature were compared with those of the pretreatment period. After the rats had been sacrificed the weights of liver, spleen and kidney were estimated and compared with those of the control. The long-term oral administration of D-Asp caused a significant decrease in the weights of total body, liver and kidney, in the daily food and fluid intake, in the weight of faeces and in the volume of urine. The osmolality of urine of the rats administered D-Asp was significantly higher than that of the control. The concomitant oral administration of L-Asp seemed to antagonize the effects of D-Asp.

Antagonistic effect of L-aspartic acid on decrease in body weight, and food and fluid intake, and naloxone reversible rectal temperature depression caused by D-aspartic acid.

Seventy-five rats, divided into five groups, were given D-aspartic acid (D-Asp), L-Asp and D + L-Asp in ratio 1/1 or 1/2 for one week. The body weight, food and fluid intakes, and rectal temperature of the rats received D-Asp or D + L-Asp in 1/1 ratio significantly decreased. The decrease in rectal temperature was antagonized by naloxone. L-Asp given together with D-Asp in 1/2 ratio prevented D-Asp-caused decrease in body weight, food and fluid intakes, and rectal temperature. Although D-amino acids, as antipeptidases have some effects through endorphinergic systems, D-Asp (an inhibitor of L-asparaginase) seems to act at the level of L-asparaginase presumably by increasing the level of endorphins since L-Asp antagonizes the inhibitory effect of both D-Asp and morphine.

The effects of D- and/or L-aspartic acids on the total weight of body, the weights of certain organs, and their protein, triglyceride and glycogen content.

125 rats which were divided into five groups were deprived of food or given orally D- (a potent inhibitor for L-asparaginase) and/or L-aspartic acids (Asp) for one week. The body weights before and at the end of the experiment were determined as well as post mortem the weights of brain, liver and kidneys, their protein contents, and the liver triglyceride and glycogen contents. D- and D+L-Asp caused significant decreases in the weights of body and liver, and in daily fluid intake; in addition liver and kidney protein, and liver triglyceride and glycogen contents were found to be lower than control. On the other hand, the food-deprived group which was subjected to more or less the same body weight loss due to food deprivation showed only a decrease in the liver triglyceride content. Since D-amino acids cause naloxone reversible analgesia which is, thus, considered as an involvement of endorphinergic system and of vasopressin, the effects of D-Asp were attributed to the changes in the availability of opioids and vasopressin, which simultaneously have an effect on each other as well as an effect of the release of ACTH. L-Asp appeared to antagonize the effects of D-Asp. Because L-Asp antagonizes the acute and chronic effects of morphine, including that on L-asparaginase activity, the hypothesis is proposed that the antagonizing effects of L-Asp observed may be caused at the level of L-asparaginase activity.

The relationship between morphine, aspartic acid and L-asparaginase in rats.

Morphine and aspartic acid were administered separately and in combination to 80 rats divided into 8 groups. Ten and 20 min following the injections, brain, liver and kidney L-asparaginase activity was determined. Morphine decreased brain and liver L-asparaginase activity and increased that of kidney. Aspartic acid completely antagonized the effect of morphine. Additionally 500 IU/kg L-asparaginase and 5 or 10 mg/kg morphine were i.v. injected into 56 rats divided into 5 groups. L-Asparaginase, which, in turn, increased motor activity, antagonized the morphine-induced hypoactivity and analgesia. These results support our previous findings.