Effect of plasma from hypertensive patients on contractile response of vascular smooth muscle from normotensive rat

This study examines whether incubation with plasma from essential hypertensive patients increases the contractile activity of vascular smooth muscle from rats in response to noradrenaline (NA) and potassium (K+). Plasma samples were obtained from age- and sex-matched essential hypertensive patients and normotensive people. Vascular strips were prepared from aorta and portal veins of normotensive rats and placed in physiological solution in muscle baths for measurement of mechanical response. Aortic strips exposed to hypertensive plasma showed increased responsiveness to NA compared with normotensive plasma, but K+ caused an opposite effect. Portal vein exposed to normotensive or hypertensive plasma did not produce any response to NA, but the responsiveness produced in the presence of normotensive plasma to K+ was higher than that of hypertensive plasma. Portal vein exposed to normotensive plasma or hypertensive plasma showed a dose-dependent increase in the spontaneous activity up to 50% concentration of the plasma samples, but further increase in the concentration of plasma inhibited the spontaneous activity. Spontaneous activity at any given concentration of hypertensive plasma was significantly higher than that of normotensive plasma. The spontaneous activity in the presence of heated or unheated normotensive plasma or unheated normotensive serum was not significantly different from each other. These results indicate that the plasma factor from hypertensive patients, which alters the reactivity of vascular smooth muscle from normotensive rat, is present in the serum fraction and is not heat sensitive.     

ACE activity during the hypotension produced by standardized aqueous extract of Cecropia glaziovii Sneth: A comparative study to captopril effects in rats

To evaluate the effect of the standardized aqueous extract (AE) of Cecropia glaziovii Sneth on the plasma angiotensin I converting enzyme (ACE-EC 3.4.15.1) activity, rats were treated with a single dose of AE (1 g/kg, p.o.) or repeatedly (0.5 g/kg/bid, p.o.) for 60 days. Captopril (50 mg/kg, p.o.) was used as positive control on the same animals. The effects on the blood pressure were recorded directly from the femoral artery (single dose), or indirectly by the tail cuff method (repeated doses) in conscious rats. The plasma ACE activity was determined spectrofluorimetrically using Hypuril-Hystidine-Leucine as substrate. The arterial blood pressure, heart rate and plasma ACE activity were not significantly modified within 24 h after a single dose administration of AE. Comparatively, blood pressure in captopril treated rats was reduced by 7-16% and heart rate was increased by 10-20% from 30 min to 24 h after drug administration. ACE activity after captopril presented a dual response: an immediate inhibition peaking at 30 min and a slow reversal to 32% up-regulation after 24 h. To correlate the drug effects upon repeated administration of either compound, normotensive rats were separated in three groups: animals with high ACE (48.8+/-2.6 nmol/min/ml), intermediate ACE (39.4+/-1.4 nmol/min/ml) and low ACE (23.5+/-0.6 nmol/min/ml) activity, significantly different among them. Repeated treatment with AE reduced the mean systolic blood pressure (121.7+/-0.5 mm Hg) by 20 mm Hg after 14 days. The hypotension was reversed upon washout 60 days afterwards. Likely, repeated captopril administration decreased blood pressure by 20 mm Hg throughout treatment in all groups. After 30 days treatment with AE (0.5 g/kg/bid, p.o.) the plasma ACE activity was unchanged in any experimental group. After captopril (50 mg/kg/bid, p.o.) administration the plasma ACE activity was inhibited by 50% within 1 h treatment but it was up-regulated by 120% after 12 h in all groups. It is concluded that the hypotension produced by prolonged treatment with AE of C. glaziovii is unrelated to ACE inhibition.     

Captopril normalises systolic blood pressure in rats with hypertension induced by fetal exposure to maternal low protein diets

Recent studies have demonstrated that the feeding of low protein diets to rats during pregnancy induces hypertension in their offspring. Maternal-diet-induced hypertension has been previously associated with elevated pulmonary angiotensin converting enzyme (ACE) activity. In the present study, the importance of the renin angiotensin system, and in particular ACE, in the maintenance of the hypertensive state, is investigated. Pulmonary and plasma ACE activity were determined in rats of different ages, following in utero exposure to 18 (control) or 9% (deficient) casein diets. No maternal diet induced changes in pulmonary ACE were noted, but at 4 and 13 weeks of age, plasma ACE activity was increased by 34 and 134%, respectively in 9% casein exposed rats relative to controls (P<0.001). Thirteen-week-old rats had significantly raised systolic blood pressure (28 mmHg, P<00.05), and tended to have higher diastolic blood pressure (not significant). These hypertensive animals had slightly raised plasma angiotensin II concentrations (30% higher, not significant), but similar renin activities, when compared with normotensive controls. Treatment of normotensive and hypertensive rats with the ACE inhibitor captopril demonstrated that higher plasma ACE activity may play a major role in the maintenance of maternal-diet-induced hypertension. Whilst normotensive rats showed no significant response to drug treatment, systolic blood pressure in the hypertensive rats fell rapidly to the level observed in the normotensive control group. Blood pressure remained at this lower level until treatment was withdrawn, at which time pressure began to increase slowly, but steadily. A period of 7–8 weeks was required following cessation of captopril administration for the restoration of hypertension.The data are consistent with the hypothesis that components of the renin-angiotensin system, and in particular plasma ACE, are involved in the maintenance of maternal-diet-induced hypertension.     

Differential prejunctional effect of captopril and saralasin on neurogenic vasoconstriction in pithed normotensive rats

The present study describes a differential inhibitory effect of captopril and [Sar1 Ala8]angiotensin II (saralasin) on the neurogenic vasoconstriction in pithed normotensive rats. In pithed normotensive rats with intact kidneys captopril more profoundly inhibited the vasopressor response to spinal stimulation than observed for saralasin. Bilateral nephrectomy also diminished the hypertensive response to spinal stimulation. After bilateral nephrectomy, 1 h previously, captopril but not saralasin diminished the hypertensive response to spinal stimulation. After bilateral nephrectomy, 18-24 h previously, captopril did not produce an additional reduction of the vasopressor response to spinal stimulation. In contrast, saralasin significantly potentiated the neurogenic vasoconstriction. The results suggest that both captopril and saralasin diminish the hypertensive response to spinal stimulation by producing dilatation of vascular smooth muscle in pithed normotensive rats. Apart from this common mechanism, a differential effect of captopril and saralasin on the neurogenic vasoconstriction can be observed. In contrast to saralasin, captopril may depress the neurogenic vasoconstriction in pithed normotensive rats by blocking the sympathofacilitatory action induced by subpressor levels of angiotensin II (AII). In pithed normotensive rats, saralasin may mimic the sympathofacilitatory action of subpressor AII.     

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 microM) and atropine (1 microM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 microM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.     

Changes in the activity of the brain renin-angiotensin system and in the functional state of the pituitary-adrenal system of rats under the influence of captopril]

While studying the effect of peroral captopril injections on the activity of renin-angiotensin system (RAS), the activity of angiotensin-converting enzyme (ACE) and angiotensin II content from anterior and mediobasal hypothalamus, medulla and adenohypophysis of intact rats has been established to decrease. Captopril administration decreases ACE activity which increases after hydrocortisone injection in rat medulla and striatum. Captopril results in no potentiation of hormonal effect in hypothalamus and in adenohypophysis where ACE activity decreases following hydrocortisone injection. A decrease in the RAS activity of brain structures and adenohypophysis induced by captopril administration to rats is accompanied by the inhibition of the activity in the pituitary-adrenal system. A decrease in ACTH level and in 11-hydroxycorticosteroids of the rat blood plasma has been determined after single captopril injection in the dosage of 10 and 50 mg/kg of body weight. Duration of the effect depends on the captopril dosage.     

Attenuation of pressor responses to intracerebroventricular angiotensin I by angiotensin converting enzyme inhibitors and their effects on systemic blood pressure in conscious rats

The components of the renin-angiotensin system exist in the brain but their physiological role is uncertain. The effects of two angiotensin converting enzyme (ACE) inhibitors, MK 421 (or its diacid) and captopril, on brain ACE activity, as measured by inhibition of the pressor response to intracerebroventricularly (i.c.v.) administered angiotensin I (AI), and the potential contribution of the central nervous system to their antihypertensive activity were evaluated in the present series of experiments. The diacid of MK 421 (1 and 10 ug) and captopril (3 and 10 ug) given i.c.v. to conscious normotensive rats reduced the pressor response to i.c.v. AI indicating that they can inhibit brain ACE. Responses to AII were unaffected. Oral administration of maximal antihypertensive doses of MK 421 (10 mg/kg) and of captopril (30 mg/kg) to normotensive rats did not attenuate pressor responses to i.c.v. AI indicating that brain ACE was not inhibited under these circumstances. Intracerebroventricular administration of MK 421 diacid, (10 and 30 ug) and captopril (30 and 100 ug) did not lower baseline blood pressure of spontaneously hypertensive rats. These experiments indicate that MK 421 and captopril can inhibit brain ACE but that the central renin-angiotensin system probably does not contribute to their antihypertensive activity.     

Feeding blueberry diets inhibits angiotensin II-converting enzyme (ACE) activity in spontaneously hypertensive stroke-prone rats

Feeding flavonoid-rich blueberries to spontaneously hypertensive stroke-prone rats (SHRSP) lowers blood pressure. To determine whether this is due to inhibition of angiotensin-converting enzyme (ACE) activity, as seen with other flavanoid-rich foods, we fed blueberries to SHRSP and normotensive rats and analyzed ACE activity in blood and tissues. After 2 weeks on a control diet, the hypertensive rats showed 56% higher levels of ACE activity in blood as compared with the normotensive rats (p < 0.05). Feeding a 3% blueberry diet for 2 weeks lowered ACE activity in the SHRSP (p < 0.05) but not the normotensive rats. ACE activity in plasma of SHRSP was no longer elevated at weeks 4 and 6, but blueberry feeding inhibited ACE in SHRSP after 6 weeks. Blueberry diets had no effect on ACE activity in lung, testis, kidney, or aorta. Our results suggest that dietary blueberries may be effective in managing early stages of hypertension, partially due to an inhibition of soluble ACE activity.     

Effect of captopril on cyclic nucleotide concentrations during long-term NO synthase inhibition

The aim of the present study was to determine the effect of angiotensin-converting enzyme inhibitor captopril on cGMP and cAMP concentration in the left ventricle and aorta after NO synthase inhibition by 4-week-lasting N(G)-nitro-L-arginine-methyl ester (L-NAME) treatment. Five groups of rats were investigated: controls, L-NAME in the dose 20 mg/kg/day (L-NAME 20), L-NAME in the dose 40 mg/kg/day (L-NAME 40), captopril in the dose 100 mg/kg/day, L-NAME 40 mg/kg/day together with captopril 100 mg/kg/day. Captopril completely prevented L-NAME-induced hypertension and LV hypertrophy development. Compared to the controls, cGMP concentration in the L-NAME 20 and L-NAME 40 groups was decreased by 13% and 22%, respectively, in the left ventricle and by 27% and 56% in the aorta, respectively. Captopril did not influence this decrease of cGMP concentration. Cyclic AMP concentration in the aorta of L-NAME 20 group increased by 17%. In the L-NAME 40 group, cAMP concentration increased by 17% in the left ventricle and by 34% in the aorta compared to controls. This increase was enhanced in rats given L-NAME together with captopril. Captopril alone had no effect on cAMP concentration. We conclude that captopril does not affect the concentration of cGMP, however, it has more than the additive effect on the cAMP concentration increase in the cardiovascular system during long-term NO synthase inhibition.     

Angiotensinase and vasopressinase activities in hypothalamus, plasma, and kidney after inhibition of angiotensin-converting enzyme: basis for a new working hypothesis

Reducing angiotensin II (Ang II) production via angiotensin-converting enzyme (ACE) inhibitors is a key approach for the treatment of hypertension. However, these inhibitors may also affect other enzymes, such as angiotensinases and vasopressinase, responsible for the metabolism of other peptides also involved in blood pressure control, such as Ang 2-10, Ang III, Ang IV, and vasopressin. We analyzed the activity of these enzymes in the hypothalamus, plasma, and kidney of normotensive adult male rats after inhibition of ACE with captopril. Aspartyl- (AspAP), glutamyl- (GluAP), alanyl- (AlaAP) and cystinyl-aminopeptidase (CysAP) activities were measured fluorimetrically using arylamides as substrates. Systolic blood pressure (SBP), water intake, and urine flow were also measured. Captopril reduced SBP and increased urine flow. In the hypothalamus, GluAP and AspAP increased, without significant changes in either AlaAP or CysAP. In contrast with effects in plasma, GluAP was unaffected, AspAP decreased, while AlaAP and CysAP increased. In the kidney, enzymatic activities did not change in the cortex, but decreased in the medulla. These data suggest that after ACE inhibition, the metabolism of Ang I in hypothalamus may lead mainly to Ang 2-10 formation. In plasma, the results suggest an increased formation of Ang IV together with increased vasopressinase activity. In the kidney, there is a reduction of vasopressinase activity in the medulla, suggesting a functional reduction of vasopressin in this location. The present data suggest the existence of alternative pathways in addition to ACE inhibition that might be involved in reducing BP after captopril treatment.     

Angiotensin-converting enzyme inhibitory and antihypertensive activities of pivalopril (RHC 3659-(S))

Pivalopril (RHC 3659-(S); (S)-N-cyclopentyl-N-(2-methyl-3-pivaloylthiopropionyl) glycine) is a new compound with a hindered sulfur group that has been compared to captopril for oral angiotensin-converting enzyme (ACE) inhibition in rats and dogs and antihypertensive activity in rats. In separate groups of conscious normotensive rats, pivalopril (0.03-1.0 mg/kg, orally [p.o.]) produced a dose-related antagonism of angiotensin I (AngI)-induced pressor effects. The ED50 for pivalopril and captopril was 0.1 mg/kg. In conscious normotensive dogs, pivalopril (incremental doses of 0.01-1.0 mg/kg, p.o.) produced a dose-related antagonism of AngI pressor effects. The ED50 was 0.17 mg/kg for pivalopril and 0.06 mg/kg for captopril. At equieffective doses the two compounds had similar durations of action. In sodium-deficient, conscious spontaneously hypertensive rats (SHR), pivalopril (1-100 mg/kg, p.o.) produced a dose-related reduction in mean arterial pressure. The potency and duration were similar to those of captopril. In the sodium-replete SHR, 5 days of oral dosing with pivalopril, 100 mg/(kg . day), decreased mean arterial pressure more effectively than captopril, 100 mg/(kg . day). No tolerance developed to the antihypertensive effect of either drug. It is concluded that pivalopril is a potent, orally effective ACE inhibitor and antihypertensive agent.     

Captopril attenuates reflex adrenergic response in essential hypertension

An attenuation of adrenergic activity during the inhibition of endogenous angiotensin II formation was evaluated by determining plasma norepinephrine concentration after a single oral administration of captopril compared to that after nifedipine in essential hypertension. Captopril produced a fall in mean arterial pressure (-24 +/- 2 mmHg, p less than 0.01) which magnitude was the same as that gained by nifedipine (-22 +/- 3 mmHg, p less than 0.01). Reflex tachycardia due to hypotension was produced (+13 +/- 1 beats/min, p less than 0.01) after nifedipine but not after captopril (-1 +/- 2 beats/min, p greater than 0.05). Although the enhancement of plasma renin activity induced by captopril (+1.54 +/- 0.56 ng/ml/hr, p less than 0.05) was similar (p greater than 0.05) to that by nifedipine (+1.44 +/- 0.47 ng/ml/hr, p less than 0.05), plasma norepinephrine concentration increased less (p less than 0.01) after captopril (+100 +/- 23 ng/ml, p less than 0.05) than after nifedipine (+283 +/- 51 ng/ml, p less than 0.05). Thus, the diminished adrenergic activity is a likely candidate for the abolished reflex tachycardia after the inhibition of angiotensin I converting enzyme activity by captopril in essential hypertension.     

Acute effects of angiotensin-converting enzyme inhibitor on erythrocyte sodium ion transport in essential hypertension.

The acute effects of angiotensin-converting enzyme inhibitor, captopril, on sodium ion transport systems were investigated in essential hypertensive and normotensive subjects. The passive sodium efflux through the erythrocyte membrane was significantly higher and erythrocyte sodium-potassium cotransport was lower in patients with essential hypertension when compared with normal subjects. However, sodium-potassium pump activity and sodium-lithium countertransport did not differ significantly between the hypertensive patients and the normal subjects. Immediately after captopril administration, erythrocyte passive sodium efflux and sodium-potassium cotransport returned to normal levels in the hypertensive subjects. Although the plasma renin activity and plasma aldosterone concentration were altered by captopril, they did not correlate with changes in any sodium transport system. These results suggest that the changes in sodium transport systems which occur immediately after captopril administration may contribute, at least in part, to its antihypertensive action.     

Inhibition of hepatic aldehyde dehydrogenases in the rat by calcium carbimide (calcium cyanamide)

Oral administration of 7.0 mg/kg calcium carbimide (calcium cyanamide, CC) to the rat produced differential inhibition of hepatic aldehyde dehydrogenase (ALDH) isozymes, as indicated by the time-course profiles of enzyme activity. The low-Km mitochondrial ALDH was most susceptible to inhibition following CC administration, with complete inhibition occurring at 0.5 h and return to control activity at 96 h. The low-Km cytosolic and high-Km mitochondrial, cytosolic, and microsomal ALDH isozymes were inhibited to a lesser degree and (or) for a shorter duration compared with the mitochondrial low-Km enzyme. The time course of carbimide, the hydrolytic product of CC, was determined in plasma following oral administration of 7.0 mg/kg CC to the rat. The maximum plasma carbimide concentration (102 ng/mL) occurred at 1 h and the apparent elimination half-life in plasma was 1.5 h. Carbimide was not measurable in the liver during the 6.5 h time interval when carbimide was present in the plasma. There were negative, linear correlations between plasma carbimide concentration and hepatic low-Km mitochondrial, low-Km cytosolic, and high-Km microsomal ALDH activities. In vitro studies demonstrated that carbimide, at concentrations obtained in plasma following oral CC administration, produced only 19% inhibition of low-Km mitochondrial ALDH and no inhibition of low-Km cytosolic and high-Km microsomal ALDH isozymes. These data demonstrate that carbimide, itself, is not primarily responsible for hepatic ALDH inhibition in vivo following oral CC administration. It would appear that carbimide must undergo metabolic conversion in vivo to inhibit hepatic ALDH enzymes, which is supported by the observation of no measurable carbimide in the liver when ALDH was maximally inhibited following oral CC administration.     

Effect of experimentally-induced hypertension on angiotensin converting enzyme activity in the aortic endothelium and smooth muscle cum adventitia of the Sprague Dawley rat.

The effect of experimentally-induced hypertension on the angiotensin converting enzyme (ACE) activity in the endothelium and smooth muscle cum adventitia of the Sprague Dawley rats was investigated. The ACE activity in both tissues of the 1-clip 2-kidney renovascular hypertensive rats and the deoxycorticosterone acetate/salt hypertensive rats were significantly higher than those of the normotensive control. These findings (i) support the suggestion that the 1-clip 2-kidney renovascular hypertensive rat represents a model of renin- and angiotensin-dependent hypertension and that the increased vascular ACE activity could play a role in the maintenance of hypertension (ii) provide new information regarding the association of increased vascular ACE activity and hypertension in the mineralocorticoid/salt treated hypertensive rats which may account for the finding by others that captopril is effective in preventing the development of hypertension in this low renin model of hypertension. On the other hand, the data also bring forth the possibility that the observed increase in vascular ACE activity could be the result of hypertension.     

Effects of continuous angiotensin I-converting enzyme blockade on blood pressure, sympathetic activity and renin-angiotensin system in stroke-prone spontaneously hypertensive rats

The purpose of this study was to examine the effects of continuous angiotensin converting enzyme (ACE) blockade in stroke-prone spontaneously hypertensive rats (sp-SHR) on the renin-angiotensin system and on sympathetic activity. The pressor response to angiotensin II (AII) and norepinephrine (NE) were also examined after chronic blockade of ACE and compared to that of saline-treated controls. Captopril treatment had no effect on body weight. Serum ACE was significantly reduced on day 1; an effect that persisted through day 6 and day 10. Plasma renin activity (PRA) was elevated significantly on day 1 and remained at this high level throughout the 10 day observation period. Plasma NE was not altered by the chronic ACE blockade except on day 1, where there was a slight elevation of plasma NE in both groups. Pressor responses to AII and NE were not changed after chronic captopril treatment. It is observed that chronic inhibition of the renin-angiotensin system with captopril in sp-SHR resulted in a reduction of blood pressure, reduced serum ACE activity and elevated PRA. The constant plasma NE levels suggest that chronic inhibition of the renin-angiotensin system does not affect sympathetic activity. This study also indicates that long term inhibition of ACE does not alter pressor responses to either AII or NE.     

Antihypertensive substance in seeds of Areca catechu L

Among various tannins tested, Areca II-5-C, a fraction isolated from seeds of Areca catechu L., showed the most potent angiotensin-converting enzyme (ACE) inhibitory activity in vitro. Its antihypertensive activity was therefore investigated in normotensive and spontaneous hypertensive rats (SHR) after both oral and intravenous (i.v.) administration. The activity was compared with that of captopril (D-3-mercapto-2-methylpropanoyl-L-proline), a potent ACE inhibitor. Oral administration of Areca II-5-C to SHR produced a lasting, dose-related antihypertensive effect, and the responses obtained with doses of 100 and 200 mg/kg were comparable to those of captopril at doses of 30 and 100 mg/kg. Intravenous administration of Areca II-5-C to SHR produced a rapid and marked reduction in blood pressure at doses of 10 and 15 mg/kg. The maximum antihypertensive effect of Areca II-5-C in SHR, at an i.v. dose of 15 mg/kg, was about 5 times as large as that of captopril at the same dose. Although the vasopressor response to norepinephrine and vasodepressor responses to bradykinin and acetylcholine were not appreciably changed by i.v. treatment with Areca II-5-C at a dose of 5 mg/kg, it did produce dose-related inhibition of the pressor responses to angiotensin I and II. It is suggested that Areca II-5-C has favorable properties as a hypotensive drug through its ability to inhibit the pressor responses to both angiotensin I and II.     

The hyperglycemic effect of S-nitrosoglutathione in the dog.

The present study investigates the pharmacological activity of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) on the plasma glucose and insulin levels in healthy normoglycemic dogs. The plasma nitrate and nitrite concentrations were measured by a commercial autoanalyzer and taken as the biochemical markers of in vivo nitric oxide formation. Plasma glucose levels were measured by the glucose oxidase method, while the insulin levels were determined by radioimmunoassay. The possible effect of the coadministration of ascorbic acid (vitamin C) and GSNO on plasma glucose levels was also examined. In healthy normoglycemic dogs, administration of 35 and 50 mg/kg of GSNO caused a dose-dependent increase in postprandial plasma glucose levels. The plasma glucose levels were significantly elevated at the 1.5-, 2.0-, and 2.5-h time intervals of the oral glucose tolerance test at both concentrations of GSNO (P < 0.05). These values were significantly higher than those obtained using captopril (control). Furthermore, coadministration of 35 mg/kg of GSNO and 50 mg/kg ascorbic acid enhanced the postprandial hyperglycaemic effect observed for the administration of only 35 mg/kg of GSNO. There was a 35-100% increase in plasma nitrate concentration on administration of both doses of GSNO. Intravenous administration of GSNO (35 mg/kg) and captopril (20 mg/kg) significantly decreased the mean arterial blood pressure and increased the heart rate. The blood pressure-lowering effect of these drugs was more pronounced on systolic than on diastolic blood pressure (P < 0.05). These results suggests that in healthy normoglycaemic dogs: (a) nitric oxide released from GSNO increases postprandial plasma glucose levels and inhibits glucose-stimulated insulin secretion, (b) ascorbic acid enhances the postprandial hyperglycaemic effect of GSNO, probably by increasing the release of NO, and (c) GSNO decreases mean arterial blood pressure and increase heart rate in normotensive dogs.     

A comparative study of the inhibition of hepatic aldehyde dehydrogenases in the rat by methyltetrazolethiol, calcium carbimide, and disulfiram

Methyltetrazolethiol (1-methyl-5-mercapto-1,2,3,4-tetrazole, MTT) is a heterocyclic substituent of the cephalosporin antibiotics, cefamandole, cefoperazone, and moxalactam. Pretreatment of rats with MTT has been reported to increase blood acetaldehyde concentration after ethanol administration. The time course of MTT-induced inhibition of hepatic aldehyde dehydrogenases (ALDH) was determined in adult, male Sprague-Dawley rats in comparison with the hepatic ALDH inhibition induced by calcium carbimide (calcium cyanamide, CC) and disulfiram (D). The apparent onset of maximal inhibition of hepatic low Km ALDH occurred at 2 h for 50 mg/kg MTT (subcutaneous, s.c.) and 7 mg/kg CC (oral) and at 24 h for 300 mg/kg D (oral). The relative magnitude of maximal inhibition of low Km ALDH was CC greater than D greater than MTT. The relative duration of enzyme inhibition was D greater than MTT greater than CC. High Km ALDH was only inhibited by CC. Hepatic low Km ALDH was selectively inhibited by s.c. and oral administration of 125 mg/kg MTT. For s.c. administration of 125 mg/kg MTT, the magnitude of maximal enzyme inhibition and the duration of inhibition were greater than for the 50 mg/kg dose. Oral administration of 125 mg/kg MTT produced similar inhibition of hepatic low Km ALDH compared with s.c. administration of the same dose. The time course of blood ethanol and acetaldehyde concentrations was determined for the intravenous infusion of two 0.3-g/kg doses of ethanol to rats that were pretreated orally with saline (1 h), MTT (125 mg/kg, 2 h), or CC (7 mg/kg, 1 h). The relative increase in blood acetaldehyde concentration compared with saline pretreatment was CC greater than MTT. The elimination of ethanol from blood was slower in the MTT- and CC-pretreated animals, and this effect was more pronounced for CC pretreatment. Overall, the data demonstrate that the characteristics of hepatic ALDH inhibition for MTT are different from those of the known ALDH inhibitors, CC and D.     

Characteristics of flutamide action on prostatic and testicular functions in the rat

The effect of daily treatment with the pure antiandrogen Flutamide has been studied either alone or in combination with the LHRH agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide (LHRH-A), on testicular and prostatic functions in adult male rats. Treatment for 10 days with Flutamide (5 mg/rat, twice daily) caused a marked stimulation of plasma testosterone (T) associated with a significant increase in plasma gonadotropin concentrations and inhibited plasma PRL levels. Testicular weight is not changed following antiandrogen administration but testicular LH/hCG receptor levels are markedly decreased with no change in FSH receptor levels. Moreover, Flutamide treatment alone produces an important inhibition of ventral prostate and seminal vesicle weights associated with a significant decrease in prostatic beta-adrenergic receptor levels but no change is observed in specific ornithine decarboxylase (ODC) activity. Daily LHRH-A treatment at the dose of 1 microgram/day for 10 days decreases plasma T to levels comparable to those found in orchiectomized men (0.30 +/- 0.5 ng/ml). This effect is associated with an almost complete loss of testicular LH/hCG receptors, a decrease in testicular weight, a significant increase in plasma gonadotropins and a marked inhibition of plasma PRL concentration. A relatively smaller inhibition of ventral prostate and seminal vesicle weights follows treatment with the LHRH agonist alone, this effect being accompanied by a significant reduction in beta-adrenergic receptor concentration but no change in prostatic ODC activity. Combination of the two drugs, however, caused a potent inhibitory effect on both ventral prostate and seminal vesicle weight to values similar to those found in castrated rats. The prostatic weight loss is accompanied by a marked fall in ODC activity and in the concentration of beta-adrenergic receptors. The present data clearly show that combined treatment with an LHRH agonist and a pure antiandrogen is highly effective in inhibiting, not only prostatic growth, but also two androgen-sensitive parameters of prostatic activity.