Effect of celecoxib on the antihypertensive effect of losartan in a rat model of renovascular hypertension

Certain nonsteroidal anti-inflammatory drugs have been reported to elevate blood pressure in some hypertensive patients, who are either untreated or treated with antihypertensive agents. This study was undertaken to determine the effect of a selective cyclooxygenase-2 (COX-2) inhibitor, celecoxib, on the antihypertensive effects of the angiotensin II type 1 receptor (AT1) antagonist, losartan potassium. We studied the effect of oral treatment with losartan (30?mg/kg), celecoxib (3?mg/kg), and their combination on the mean arterial blood pressure (MAP), plasma renin activity (PRA), and plasma prostaglandin E2 (PGE2) in male Sprague-Dawley rats with renovascular hypertension (RVH) induced by partial subdiaphragmatic aortic constriction. Treatment was continued for 7 days after aortic coarctation. Aortic coarctation led to significant increases in the MAP, PRA, and plasma PGE2. In RVH rats, losartan treatment caused a significant decrease of MAP with a significant increase in both plasma PGE2 and PRA. Celecoxib caused a nonsignificant change in MAP with a significant decrease in the raised levels of plasma PGE2 and PRA. Concomitant administration of celecoxib and losartan did not significantly affect the lowering effect of losartan on MAP with a subsequent significant decrease in the plasma PGE2 and PRA in RVH rats. Therefore, celecoxib could be used in renin-dependent hypertensive patients who receive losartan, without fear of a rise in their blood pressure.     

Mechanism for the increase in plasma renin activity by pentobarbital anesthesia

The mechanism by which pentobarbital anesthesia causes increases in plasma renin activity (PRA) was examined in dogs infused with either propranolol or indomethacin, an inhibitor of prostaglandin synthetase. Infusion of propranolol at 1 mg/kg, (I.V.) followed by 0.6–0.7 mg/kg/hr decreased PRA from 6.98±2.49 ng/m1/hr during control periods to 1.58±0.79 ng/m1/hr 30 minutes after the injection of propranolol (P<0.025). Subsequent induction of anesthesia with sodium pentobarbital caused PRA to rise to 3.87±0.93 ng/m1/hr in 30 minutes. (P<0.01). Plasma potassium concentration decreased from 4.6±0.2 mEq/L to reach 4.0±0.1 mEq/L 30 minutes after induction of anesthesia (P<0.005). Infusion of indomethacin at 5 mg/kg, (I.V.) followed by 1.5 ? 3.1 mg/kg/hr into conscious dogs did not decrease PRA. In contrast to the report by Montgomery et al (Fed. Proc. 36: 989, 1977), we found that the increase in PRA after pentobarbital anesthesia could not be blocked by indomethacin. PRA was 5.3±1.2 ng/m1/hr(M ± SEM) during control periods and was 4.7±1.4 ng/m1/hr 30 minutes after the infusion of indomethacin (P<0.1). PRA increased to 10.9±2.3 ng/m1/hr, 9.2±2.2 ng/m1/hr, and 7.7±1.7 ng/m1/hr at 5, 15 and 30 minutes, respectively, after the administration of pentobarbital (P<0.005, P<0.025, P<0.05). PRA declined to 4.2±1.3 ng/m1/hr 60 minutes after pentobarbital anesthesia (P<0.1). It is concluded that the mechanism by which pentobarbital causes increases in PRA is independent of prostaglandins.     

Influence of adrenergic nervous and prostaglandin systems on hydralazine-induced renin release

The role of the beta-adrenergic nervous and prostaglandin systems in vasodilator-induced activation of the renin-angiotensin system was studied in conscious rats. The plasma renin activity (PRA) response to intravenous hydralazine (0.25, 0.5 and 1 mg/kg body wt.) was compared to the PRA response following administration of similar doses of hydralazine to rats pretreated with either indomethacin (3 mg/kg body wt. i.v.) or indomethacin and propranolol (1 mg/kg body wt. i.v.). PRA increased significantly above control levels after each of the hydralazine doses. In rats pretreated with indomethacin, PRA did not increase with the 0.25 mg/kg dose of hydralazine; increased significantly with the 0.5 mg/kg dose but remained significantly lower than the PRA response in the absence of indomethacin; and increased with the 1 mg/kg dose to a level not significantly different from PRA in rats receiving only hydralazine. When rats were pretreated with indomethacin and propranolol, PRA did not increase significantly in response to either the 0.25 or 0.5 mg/kg doses of hydralazine. Although a statistically significant increase in PRA was noted with the 1 mg/kg dose of hydralazine, the level of PRA achieved was very low and only 15% of that observed with the other two treatment regimens (i.e., hydralazine alone or indomethacin and hydralazine). These results demonstrate that vasodilator-induced renin release is only partially mediated via the prostaglandin system, that the degree of this control is related to the intensity of vasodilator stimulus and that renin release following administration of hydralazine can be attributed almost entirely to activation of the beta-adrenergic nervous and prostaglandin systems.     

In vitro evidence for a blood-borne renin-releasing factor

The present studies using kidney slices were designed to test whether serotonergic stimulation of renin secretion is mediated via an endocrine signal. Previous in vivo studies have indicated that central serotonergic neurons regulate renin secretion. Administration of the serotonin releaser dl-p-chloroamphetamine-HCl (PCA) to rats causes dose-dependent increases in renin secretion that can be blocked by serotonin depletion with p-chlorophenylalanine (PCPA), injections of 5,7-dihydroxytryptamine into the dorsal raphe nucleus or ablation of the mediobasal hypothalamus. The renin-releasing substance was obtained from nephrectomized male donor rats which were sacrificed 1 hour after receiving an injection of PCA intraperitoneally. Plasma from rats that received saline injections was used as control. The plasma was collected and separated by ultrafiltration into fractions containing solutes with molecular weights between 500-10,000 daltons. The renin-releasing ability of this substance was studied in vitro using rat renal cortical slices. The plasma fraction (M.W. = 500 - 10,000) from rats treated with PCA caused dose-dependent increases in renin release from the kidney slices. Heating of the plasma factor at 100 degrees C for 30 minutes did not reduce the ability of this substance to release renin from the kidney slices. PCA alone (66 X 10(-6)M) did not increase renin release from the kidney slices. These data suggest that stimulation of serotonergic receptors in the brain triggers the release of an endocrine factor that is capable of directly stimulating renin release from the kidneys.     

Opiate and alpha receptor antagonists block the pressor responses of conscious rats given intravenous dynorphin

Conscious, unrestrained rats were used to determine the hemodynamic (blood pressure and heart rate) responses following intravenous (IV) injection of dynorphin A(1-13) and the possible receptor mechanisms mediating those changes. Male Sprague-Dawley rats (300 g) were given IV bolus injections (via femoral venous catheter) of 6.0 to 600 nmoles/kg of dynorphin A(1-13), 8.0 nmoles/kg of norepinephrine HCl (NE), 14.3 pmoles/kg of angiotensin II or a vehicle control solution. Blood pressure (BP) and heart rate (HR) were monitored via femoral arterial catheter (into abdominal aorta) over 90 sec postpeptide or -amine administration before and 10 min after IV injection of 4.2 mumoles/kg of naloxone HCl (opiate antagonist), yohimbine HCl (alpha 2 receptor antagonist) or prazosin HCl (alpha 1 receptor antagonist). Dynorphin A(1-13) caused a transient but dose-related rise in mean arterial pressure (MAP) whereas mean pulse pressures (MPP) and mean heart rates (MHR) concomitantly fell, from preinjection control values in a dose-dependent fashion. Pretreatment with naloxone blocked the pressor response of only a subsequent injection with 20 nmoles/kg but not 60 nmoles/kg of dynorphin A or NE (8.0 nmoles/kg). Pretreatment with yohimbine suppressed the marked pressor responses of subsequent NE or Dyn A (60 nmoles/kg) administration whereas prazosin antagonized the rise in MAP of only the lower doses of dynorphin as well as NE. The suppression of the pressor responses of dynorphin by opiate or alpha receptor antagonists were not caused by tachyphylaxis for repeated injections of 6.0 or 60 nmoles/kg of dynorphin caused the same rise in MAP.(ABSTRACT TRUNCATED AT 250 WORDS)     

异搏定对四氧嘧啶损害大鼠胰岛β细胞的保护作用

本工作用四氧嘧啶(尾静脉注射)造成大鼠实验性糖尿病模型。若预先由腹腔注射异搏定(40mg/kg)则可使大鼠血糖水平明显降低,不产生糖尿病,注射四氧嘧啶后48h,血糖浓度的平均值由22.93±1.37mmol/L下降到8.79±0.83mmol/L。口服葡萄糖耐量试验观察到,经过异搏定处理的糖尿病大鼠,在注射四氧嘧啶后的48h,其胰岛素分泌功能较未经异搏定处理的糖尿病大鼠有明显的恢复。组织学切片也显示,胰岛β细胞内胰岛素分泌颗粒的含量在异搏定处理组较单独四氧嘧啶处理组明显增多。上述结果表明,预先注射异搏定能减轻四氧嘧啶对胰岛β细胞造成的急性损伤。     

Parathyroid hormone-related protein stimulates plasma renin activity via its anorexic effects on sodium chloride intake

Parathyroid hormone-related protein (PTHrP) increases renin release from isolated perfused kidneys and may act as an autacoid regulator of renin secretion, but its effects on renin in vivo are unknown. In vivo, PTHrP causes hypercalcemia and anorexia, which may affect renin. We hypothesized that chronically elevated PTHrP would increase plasma renin activity (PRA) indirectly via its anorexic effects, reducing sodium chloride (NaCl) intake and causing NaCl restriction. We infused male Sprague-Dawley rats with the vehicle (control) or 125 μg PTHrP/day (PTHrP) via subcutaneous osmotic minipumps for 5 days. To replenish NaCl consumption, a third group of PTHrP-infused rats received 0.3% NaCl (PTHrP + NaCl) in their drinking water. PTHrP increased PRA from a median control value of 3.68 to 18.4 ng Ang I·ml(-1)·h(-1) (P < 0.05), whereas the median PTHrP + NaCl PRA value was normal (7.82 ng Ang I·ml(-1)·h(-1), P < 0.05 vs. PTHrP). Plasma Ca(2+) (median control: 10.2 mg/dl; PTHrP: 13.7 mg/dl; PTHrP + NaCl: 14.1 mg/dl; P < 0.05) and PTHrP (median control: 0.03 ng/ml; PTHrP: 0.12 ng/ml; PTHrP + NaCl: 0.15 ng/ml; P < 0.05) were elevated in PTHrP- and PTHrP + NaCl-treated rats. Body weights and caloric consumption were lower in PTHrP- and PTHrP + NaCl-treated rats. NaCl consumption was lower in PTHrP-treated rats (mean Na(+): 28.5 ± 4.1 mg/day; mean Cl(-): 47.8 mg/day) compared with controls (Na(+): 67.3 ± 2.7 mg/day; Cl(-): 112.8 ± 4.6 mg/day; P < 0.05). NaCl consumption was comparable with control in the PTHrP + NaCl group; 0.3% NaCl in the drinking water had no effect on PRA in normal rats. Thus, our data support the hypothesis that PTHrP increases PRA via its anorexic effects, reducing NaCl intake and causing NaCl restriction.     

Changes in central and peripheral renin-angiotensin system after furosemide injection

To examine the effects of acute stimulation on the peripheral and central renin-angiotensin system, simultaneous sampling of blood and cerebrospinal fluid (CSF) for measurements of plasma renin activity (PRA), plasma angiotensin I-immunoreactivity (PAng I-ir), plasma angiotensin II-immunoreactivity (PAng II-ir), plasma angiotensinogen and cerebrospinal fluid angiotensin II-ir (CSF Ang II-ir) and CSF angiotensinogen was carried out following intravenous injection of furosemide (5 mg/kg) in conscious dogs. Administration of furosemide induced marked increases in PRA, Ang I-ir, PAng II-ir and CSF Ang II-ir, however, neither plasma nor CSF angiotensinogen was changed. Furthermore, a relatively large dose (20 mg/kg/min) of intravenously infused synthetic Ang II for 20 min produced a five-fold increase in PAng II-ir compared with no significant increase in CSF Ang II-ir. In spite of significant suppression of PRA and PAng I-ir, there were no significant changes in either plasma or CSF angiotensinogen. These results primarily suggest that the peripheral and the brain renin-angiotensin systems may be linked and that acute changes in the peripheral renin-angiotensin system do not alter either plasma or CSF angiotensinogen.     

Ejaculations induced by p-chloroamphetamine (PCA) in rats, hamsters and mice.

The ejaculatory response induced by p-chloroamphetamine (PCA) in male rats, hamsters and mice was observed during 2 hours after the injection. The animals were treated intraperitoneally with PCA at doses ranging from 0.78125 to 160 mg/kg. The ED50 (effective dose in 50% of animals) values of PCA for the initiation of ejaculation in rats and hamsters were 1.3397 (1.0732-1.6725) and 0.1105 (0.0802-0.1522) mg/kg, respectively. On the other hand, no ejaculation was observed in any mice at any doses examined. So we concluded that there are species differences in the ejaculatory response, induced by PCA, among rats, hamsters and mice.     

Effect of brain serotonin on the arterial pressure and plasma renin in normal and hypertensive rats]

The effects of changes in brain serotonin content after injections of p-chlorophenylalanine (p-CPA), L-5-hydroxytryptophan (L-5HTP) and 5-6-dihydroxytryptamine (5-6DHT) on the mean arterial pressure (MAP), plasma renin activity (PRA) and peripheral levels of atrial natriuretic peptide (ANP) have been studied in normal and hypertensive (2K:1C model) male Wistar rats. The p-CPA (250 mg/kg) and L-5HTP (200 mg/kg) were injected i.p., while 5-6 DHT (15 micrograms/animal in 10 mu/animal vehicle) was injected into lateral brain ventricles. The effects were studied 24 h after the p-CPA injection, 2 h after L-5HTP and 10 or 20 days after 5-6DHT administration. The fall in brain serotonin produced by p-CPA and 5-6DHT did not modify the MAP values in the normal and hypertensive rat model, whereas the increase induced after L-5HTP injection only caused a slight decrease in arterial pressure in normotensive animals. The ARP experimented remarkable rises in the normal and hypertensive rats, these values increasing after L-5HTP and falling after p-CPA and 5-6 DHT injections. Similar changes are detected in the normal group after administration of these substances related to serotoninergic brain activity. The ANP levels rose after renal artery constriction, and they are not affected by the above mentioned substances. Only p-CPA and 5-6DHT reduced a low decrease in the ANP levels 10 days after their administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolonged blood pressure reduction by orally active renin inhibitor RO 42-5892 in essential hypertension.

OBJECTIVE--To investigate the effects of a novel specific renin inhibitor, RO 42-5892, with high affinity for human renin (Ki = 0.5 x 10(-9) mol/l), on plasma renin activity and angiotensin II concentration and on 24 hour ambulatory blood pressure in essential hypertension. DESIGN--Exploratory study in which active treatment was preceded by placebo. SETTING--Inpatient unit of teaching hospital. PATIENTS--Nine men with uncomplicated essential hypertension who had a normal sodium intake. INTERVENTIONS--Two single intravenous doses of RO 42-5892 (100 and 1,000 micrograms/kg in 10 minutes) given to six patients and one single oral dose (600 mg) given to the three others as well as to three of the patients who also received the two intravenous doses. RESULTS--With both intravenous and oral doses renin activity fell in 10 minutes to undetectably low values, while angiotensin II concentration fell overall by 80-90% with intravenous dosing and by 30-40% after the oral dose. Angiotensin II concentration was back to baseline four hours after the low and six hours after the high intravenous dose and remained low for at least eight hours after the oral dose. Blood pressure fell rapidly both after low and high intravenous doses and after the oral dose and remained low for hours. With the high intravenous dose the daytime (0900-2230), night time (2300-0600), and next morning (0630-0830) systolic blood pressures were significantly (p less than 0.05) lowered by 12.5 (95% confidence interval 5.6 to 19.7), 12.2 (5.4 to 19.3), and 10.7 (3.2 to 18.5) mm Hg respectively, and daytime diastolic pressure was lowered by 9.3 (2.2 to 16.8) mmHg. With the oral dose daytime, night time, and next morning systolic blood pressures were lowered by 10.3 (5.5 to 15.4), 10.5 (4.2 to 17.2), and 9.7 (4.0 to 15.6) mm Hg, and daytime and night time diastolic pressures were lowered by 5.8 (0.9 to 11.0) and 6.0 (0.3-12) mm Hg respectively. CONCLUSIONS--The effect of the inhibitor on blood pressure was maintained over a longer period than its effect on angiotensin II. RO 42-5892 is orally active and has a prolonged antihypertensive effect in patients who did not have sodium depletion. This prolonged effect seems to be independent, at least in part, of the suppression of circulating angiotensin II.     

Role of renin-angiotensin system in hypotension-evoked thirst: studies with hydralazine

Injection of rats either with diazoxide (25 mg/kg iv), isoproterenol (0.33 mg/kg sc), or hydralazine (HDZ) (10 mg/kg ip) decreased arterial blood pressure from approximately 120 to 70-80 mmHg and stimulated renin secretion. However, diazoxide and isoproterenol treatments each stimulated water ingestion, whereas HDZ treatment did not. HDZ treatment did not reduce water intake evoked by systemic injection of hypertonic saline or 20% polyethylene glycol solution or by 24-h water deprivation, suggesting that HDZ treatment did not interfere with drinking behavior. In contrast, HDZ treatment markedly reduced water intake evoked by injection of diazoxide or isoproterenol or by intravenous infusion of renin. Furthermore, a highly significant correlation was observed when plasma ANG II levels were plotted as a function of plasma renin activity after intravenous infusion of renin and after diazoxide and isoproterenol treatments. However, values obtained after HDZ treatment alone or in combination with intravenous infusion of renin did not fall near the 99% confidence interval of the regression line, suggesting that HDZ treatment blocks ANG II production and/or promotes its clearance. Thus rats apparently do not increase water intake after HDZ treatment, because this drug interferes with the renin-angiotensin system. These results provide further evidence that arterial hypotension evokes thirst in rats predominantly by activation of the renin-angiotensin system.     

Effect of prolonged ACTH stimulation on adrenal renin and aldosterone

Changes in adrenal renin, which have been regarded as mediator of aldosterone secretion in the adrenal gland, following prolonged ACTH treatment were investigated in male Wistar rats. After 2 days of daily sc injection of ACTH (Cortrosyn-Zinc, 50 micrograms/day), parallel increases in adrenal renin and aldosterone, and plasma aldosterone (PA) were induced. The plasma renin activity (PRA) was slightly but not significantly decreased. Prolonged treatment with ACTH for 8 days increased the adrenal renin, causing a marked reduction in the adrenal aldosterone concentration. The degree of decrease in the PRA was again not significant and similar to that after 2 days of ACTH treatment. Contrary to previout reports which have indicated participation of adrenal renin in the regulation of aldosterone secretion in the adrenal gland, the present results showed reciprocal changes in adrenal renin and aldosterone after prolonged treatment with ACTH. The present findings suggest a complicated relation between adrenal renin and aldosterone secretion in the adrenal gland.     

Role of antidiuretic activity in the inhibition of renin secretion by vasopressin in anesthetized dogs

The nature of the activity of vasopressin which is responsible for the inhibition of renin secretion was studied by comparing the effects of vasopressin (AVP) and analogs of AVP in anesthetized water-loaded dogs. Infusion of AVP (1.0 ng/kg/min) increased mean arterial pressure (MAP) and decreased heart rate (HR) and free water clearance (CH2O). Plasma renin activity (PRA) decreased from 11.9 +/- 4.7 to 3.8 +/- 1.7 ng/ml/3 hr (p less than 0.05). A selective antidiuretic agonist, 1-deamino-8-D-arginine vasopressin (1.0 ng/kg/min), which had no effect on MAP or HR but was effective as AVP in decreasing CH2O, decreased PRA from 13.5 +/- 4.6 to 7.0 +/- 2.9 ng/ml/3 hr (p less than 0.05). Infusion of a selective vasoconstrictor agonist, 2-phenylalanine-8-ornithine oxytocin (1.0 ng/kg/min), increased MAP and decreased HR but did not decrease CH2O or PRA. A vasoconstrictor antagonist, d(CH2)5Tyr(Me)AVP (10 micrograms/kg), completely blocked the MAP and HR responses to AVP but did not block the decrease in CH2O or PRA (5.9 +/- 1.8 to 2.9 +/- 1.6 ng/ml/3 hr) (p less than 0.001). Infusion of the 0.45% saline vehicle had no significant effect on MAP, HR, CH2O or PRA. These results indicate that the inhibition of renin secretion by vasopressin in anesthetized water-loaded dogs is due to its antidiuretic activity.     

Pathogenic mechanisms of acute pulmonary edema of hemodynamic origin in rats]

In normal anaesthetized rats (pentobarbital, 40 mg/kg i.p.), intravenous injection of a bolus of vasopressin (0.3 micrograms/kg) provoked a large increase in pulmonary and in systemic blood pressures. About three minutes later, some rats (60%) developed an acute pulmonary edema (OPA), froth appearing at the trachea. Other animals presented no OPA at the 4th minute following the injection, but OPA appeared immediately when bilateral vagotomy was performed at that time. Factors explaining the appearance of OPA are mechanical ones, circulatory or respiratory, without interferences with autonomous nervous processes.     

Effect of lithium preparations on the toxic effects of adrenaline

Experiments on rats have shown that intravenous injection of adrenaline in a dose of 0.3-0.4 mg/kg causes cardiac arrhythmia. In this case the primary arrhythmia developing immediately after adrenaline injection is followed by the recovery of sinusal rhythm which was replaced by the secondary arrhythmia. Apart from arrhythmias, there developed pulmonary edema. The animals died 2--3 minutes after adrenaline injections. Lithium chloride and lithium hydroxybutyrate removed the secondary arrhythmia and pulmonary edema. Lithium hydroxybutyrate has proved to be more effective.     

The human renin infused rat: use as an in vivo model for the biological evaluation of human renin inhibitors

The human renin infused rat model (HRIRM) was used as an in vivo small-animal model for evaluating the efficacy of a collection of inhibitors of human renin. The intravenous infusion of recombinant human renin (2.4 microg x kg(-1) x min(-1)) in the ganglion-blocked, nephrectomized rat produced a mean blood pressor response of 47+/-3 mm Hg (1 mm Hg = 133.3 Pa), which was reduced by captopril, enalkiren, and losartan in a dose-dependent manner following oral administration, with ED50 values of 0.3+/-0.1, 2.5+/-0.9, and 5.2+/-1.6 mg/kg, respectively. A series of peptidomimetic P2-P3 butanediamide renin inhibitors inhibited purified recombinant human renin in vitro in a concentration-dependent manner, with IC50 values ranging from 0.4 to 20 nM at pH 6.0, with a higher range of IC50 values (0.8-80 nM) observed at pH 7.4. Following i.v. administration of renin inhibitors, the pressor response to infused human renin in the HRIRM was inhibited in a dose-dependent manner, with ED50 values ranging from 4 to 600 microg/kg. The in vivo inhibition of human renin following i.v. administration in the rat correlated significantly better with the in vitro inhibition of human renin at pH 7.4 (r = 0.8) compared with pH 6.0 (r = 0.5). Oral administration of renin inhibitors also resulted in a dose-dependent inhibition of the pressor response to infused human renin, with ED50 values ranging from 0.4 to 6.0 mg/kg and the identification of six renin inhibitors with an oral potency of <1 mg/kg. The ED50 of renin inhibitors for inhibition of angiotensin I formation in vivo was highly correlated (r = 0.9) with the ED50 for inhibition of the pressor response. These results demonstrate the high potency, dose dependence, and availability following oral administration of the butanediamide series of renin inhibitors.     

Effects of an angiotensin II antagonist; [sarcosine 1, isoleucine 8] angiotensin II, on blood pressure, plasma renin activity and plasma aldosterone concentration in hypertensive and normotensive subjects taking oral contraceptives.

To examine the involvement of renin-angiotensin-aldosterone system in the etiology of oral contraceptive induced hypertension, normal women (Group I), normotensive (Group II) and hypertensive (Group III) women taking Ovulen (R) were infused with a competitive angiotensin II (AII) antagonist, [1-sarcosine, 8-isoleucine] angiotensin II. The angiotensin II antagonist was infused at a rate of 600 ng/kg/min for 30 min 1.5 hrs after intravenous injection of 40 mg of furosemide. Blood pressure was monitored and pre-infusion and post-infusion plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were determined. Pre-infusion PRA and PAC showed no significant differences among these three groups. In response to the AII antagonist infusion blood pressure rose in Groups I and II, but blood pressure responses in Group III were variable. Four out of the total 6 subjects had pressor responses and only one subject had a significant blood pressure reduction. In both Groups I and II, PRA decreased and PAC rose after infusion of the antagonist. In Group III, PRA decreased to a lesser degree and PAC showed no consistent change. These data suggest that the renin-angiotensin-aldosterone system in hypertensive women or oral contraceptives is different from that of the normotensive users. However, the pathophysiology of oral contraceptive induced hypertension is not homogenous and angiotensinogenic hypertension is uncommon.     

Oxytocin antagonist disrupts hypotension-evoked renin secretion and other responses in conscious rats

Previous experiments have indicated that arterial hypotension increases plasma oxytocin (OT) levels in rats and that OT infused intravenously causes an increase in plasma renin activity (PRA). The goal of the present study was to determine whether systemic administration of an OT receptor antagonist would attenuate the increase in PRA that is normally evoked by arterial hypotension in rats. In conscious male rats, intravenous injection of hydralazine or diazoxide produced sustained hypotension and evoked a significant increase in PRA, as expected. Intravenous infusion of an OT receptor antagonist did not alter the hypotension induced by hydralazine or diazoxide, but it did markedly blunt the induced increase in PRA. The OT receptor antagonist also blunted the hypotension-evoked increase in heart rate and plasma vasopressin levels, suggesting that the antagonist may have generally disrupted afferent signaling of hypotension. Thus hypotension-evoked OT secretion may contribute to cardiovascular homeostasis by enhancing baroreceptor signals that stimulate increases in renin secretion, vasopressin secretion, and heart rate during arterial hypotension in rats.     

Involvement of vagal opioid receptors in respiratory effects of morphine in anaesthetized rats.

Respiratory effects of morphine injection to the femoral vein were investigated in urethane and chloralose anaesthetized and spontaneously breathing rats, prior to and after midcervical vagotomy. Bolus injection of morphine HCl at a dose of 2 mg/kg of body weight induced depression of ventilation in all rats, due to the significant decrease in tidal volume and to the decline in respiratory rate both pre- and post-vagotomy. Expiratory apnoea of mean duration of 10.0+/-3.4 s was present in the vagally intact rats only. Bilateral midcervical section of the vagus nerve precluded the occurrence of apnoea. Prolongation of the expiratory time (T(E morphine) / T(E control)), which amounted to 10.7+/-2.2-fold in the intact state, was apparently reduced to 1.5+/-0.3-fold after division of the vagi. Morphine significantly decreased mean arterial pressure (MAP) at 30 s after the challenge, the effect persisted for not less than 1 minute and was absent in vagotomized rats. The respiratory changes evoked by morphine reverted to the control level after intravenous injection of naloxone at a dose of 1 mg/kg. Results of this study indicate that opioid receptors on vagal afferents are responsible for the occurrence of apnoea and hypotension evoked by morphine.