Effects of angiotensin I converting enzyme inhibitor (SQ 14,225) on the responses of blood pressure and steroid hormone to angiotensin II and ACTH infusion in hypertensive subjects

The effects of the converting enzyme inhibitor, SQ 14,225, on the renin-angiotensin system, adrenal function and blood pressure were investigated in 14 hypertensive patients, i.e., 10 with essential hypertension (EH) and 4 with renovascular hypertension (RVH). The mean blood pressure (MBP) and plasma aldosterone showed significant decreases in the EH with normal renin (NR) group and in the RVH group but no significant changes in the EH with low renin (LR) group. Plasma renin activity (PRA) increased significantly in the EH and NR group and in the RVH group but showed no significant change in the EH with LR group. Significant correlations were found between the fall in MBP after SQ 14,225 treatment and the pretreatment levels of PRA or plasma aldosterone. In an ACTH infusion study, the response of plasma aldosterone to ACTH revealed significant decreases after SQ 14,225 administration. In an angiotensin II (A II) infusion study, the response of plasma aldosterone was unchanged after SQ 14,225 administration. However, the pressor responses to A II infusion with SQ 14,225 were significantly higher than those without SQ 14,225. From these findings, it is concluded that the antihypertensive mechanism of SQ 14,225 may be due mainly to the decrease in levels of endogenous A II and that the reduction in plasma aldosterone after SQ 14,225 were significantly higher than those without SQ 14,225. From these findings, it is concluded that the antihypertensive mechanism of SQ 14,225 administration may be due to reduction of endogenous A II levels by converting enzyme inhibition.     

Effect of Chronic Blockade of the Kallikrein-Kinin System on the Development of Hypertension in Rats

-The kallikrein-kininogen-kinin system is an important vasodilator and vasodepressor component of the cardiovascular system. Acting mainly through B(2) receptors, kinins may counterbalance the pressor effect of angiotensin II, salt, and mineralocorticoids plus salt. Using rats lacking the bradykinin precursors low- and high-molecular-weight kininogen or a B(2) kinin receptor antagonist (icatibant), we investigated whether absence or blockade of the kallikrein-kinin system alters blood pressure (BP) in rats given (1) chronic infusion of Ang II, (2) a normal or high salt diet, or (3) chronic administration of deoxycorticosterone acetate (DOCA) plus salt. We confirmed the genotype and phenotype of Brown Norway Katholiek rats (BNK) and found that they had a G-to-A point mutation on the kininogen gene compared with Brown Norway (BN) and Sprague-Dawley (SD) rats, very low levels of high-molecular-weight kininogen (17+/-3 ng/mL) compared with BN and SD (1814+/-253 and 2397+/-302 ng/mL, respectively; P:<0.01), and plasma low-molecular-weight kininogen concentrations below detectable limits compared with 1773+/-74 and 1781+/-140 ng/mL for BN and SD, respectively. Basal BP was the same in BNK and BN. Chronic infusion of icatibant did not alter BP in BN or Wistar rats. At doses that blocked the acute effect of bradykinin, icatibant did not potentiate the pressor effect of a chronic subpressor or pressor dose of angiotensin II in male and female Wistar rats nor that of a high salt diet (2%) plus unilateral nephrectomy in male Wistar rats. Moreover, blockade of the kallikrein-kininogen-kinin system in either BN rats given a very high dose of icatibant or kinin-deficient rats (BNK) did not potentiate the pressor effect of angiotensin II (nonpressor dose) or a high salt (3% NaCl) diet given for 2 weeks. Established DOCA-salt hypertension was not exaggerated in rats treated with icatibant but was partially attenuated by ramipril (1.5 mg. kg(-)(1). d(-)(1) for 7 days; P:<0.002). This antihypertensive effect was abolished by icatibant (P:<0.002, ramipril versus ramipril plus icatibant). These results suggest that endogenous kinins do not participate in the maintenance of normal blood pressure or antagonize the development of hypertension induced by chronic infusion of angiotensin II, a high salt diet, or DOCA-salt. However, kinins appear to play an important role in the antihypertensive effect of angiotensin-converting enzyme inhibitors in DOCA-salt hypertension.     

The antihypertensive effect of captopril. Evidence for an influence of kinins

The acute effect of the orally-active converting enzyme inhibitor, captopril, was compared to that of saralasin in 13 patients with various forms of hypertension on ad libitum sodium intake. A significant difference between the effects of the two drugs on mean arterial pressure (MAP) was found (-11 +/- 3 mm Hg with saralasin, -24 +/- 4.5 mm Hg after captopril). This difference was not correlated with control plasma renin activity (PRA). To determine the influence of the endogenous kallikrein-kinin system in the antihypertensive action of captopril, the effect of aprotinin (Apro), an inhibitor of kinin generation, on the MAP level achieved by captopril was assessed in five normal subjects and 15 patients with hypertension on ad libitum sodium intake. In normal subjects, captopril did not alter MAP, nor did Apro have any effect. In six patients with essential hypertension and normal PRA, MAP decreased by 5.5 +/- 2 mm Hg following captopril, and Apro did not modify this level. In nine patients with renovascular hypertension (RVH), MAP fell by 22 +/ 3 mm Hg after captopril administration, and Apro infusion induced a rise in MAP of 13 +/- 1.7 mm Hg. A positive correlation between log control PRA and the effect of aprotinin was obtained ( r = 0.63, p less than 0.005). Apro had no effect in two patients with RVH who experiences a large drop in MAP during salasin. These results suggest that endogenous kinins as well as other substances, the generation of which is inhibited by aprotinin, may participate to the antihypertensive effect of captopril in patients with angiotensin-dependent hypertension. The lack of an aprotinin effect on the MAP level achieved during saralasin infusion suggests that the influence of the kallikrein-kinin system is related to the effect of captopril rather than the fall in arterial pressure resulting from angiotensin blockade.     

Role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor, captopril

The role of kinins in the acute antihypertensive effect of a converting enzyme inhibitor (CEI) was studied in sodium-depleted normotensive and in two-kidney, one clip chronically hypertensive rats (2K-1C). The 2K-1C were on a normal sodium diet. The acute vasodepressor effect of the CEI was determined in these two groups either after administration of normal rabbit globulins or antikinin globulins. The amount of kinin antibodies administered completely blocked the hypotensive effects of bradykinin, 400 ng/kg, and urinary kallikrein, 4 microgram/kg. After administration of CEI in the sodium-depleted rats there was no significant difference (p greater than 0.05) in the acute changes in mean blood pressure (BP) between the group pretreated with normal rabbit globulins (delta BP -32.3 +/- 3.9 mm Hg) and the group pretreated with antikinin globulins (delta BP -25 +/- 2.5 mm Hg). In the 2K-1C pretreated with normal rabbit globulins, the CEI produced a decrease in BP of -21 +/- 4.5 mm Hg. This decrease was almost completely blocked in the group pretreated with the antikinin globulins (delta BP -4 +/- 4.1 mm Hg). These differences in the changes in BP were significant (p less than 0.02). These results suggest that the acute antihypertensive effect of the CEI in the sodium-depleted rats is probably due to inhibition of the conversion of angiotensin I to II while in the 2K-1C it is due, in part, to an increase in kinin concentrations secondary to the inhibition of kininase II.     

The hemodynamic effect of dietary calcium supplementation on rat renovascular hypertension

Summary Mechanisms which could be responsible for the hypotensive effects of increasing calcium intake from 1.2 to 2.5% of diet were examined in two kidney, one clip renovascular hypertension (2K, 1C RHV) in male Sprague-Dawley rats. Plasma renin activity was elevated similarly in NCA and HCA rats. No evidence for volume or phosphate depletion was found in HCA animals. Cardiac output was not different. Decreased sensitivity was demonstrated to moderate doses of norepinephrine in HCA rats, while vascular reactivity to exogenously administered angiotensin II over the range of doses used was not different between diets. The antihypertensive effect of supplemental calcium was associated with a 39% reduction in systemic vascular resistance. Therefore, dietary calcium supplementation lowers blood pressure in 2-K, 1C RVH primarily due to a systemic vasodilatation and reduced vascular reactivity to moderate doses of norepinephrine.     

Haemodynamic response to magnesium administration in mineralocorticoid-salt and two-kidney, one clip renovascular hypertension

Recent interest has centred on the role of divalent cations in hypertension, particularly in relation to the renin-angiotensin system. This study was undertaken to determine the hypotensive effect of magnesium administration in relation to the state of activation of the renin-angiotensin system. The mean blood pressure (MBP) and heart rate (HR) response to either the acute intravenous administration of a pharmacological dose of MgSO4 or vehicle was determined in conscious mineralocorticoid-salt (DOCA-salt, low-renin) and two-kidney, one clip renovascular, high-renin hypertensive rats. Baseline MBP was higher in the renovascular than in the DOCA-salt rats, while there was no difference in HR or serum Mg concentration between the two. Following administration of MgSO4, serum Mg increased equally in both the DOCA-salt (1.4 +/- 0.8 to 4.9 +/- 0.16 mEq/l; P less than 0.001) and in the renovascular rats (1.8 +/- 0.14 to 4.4 +/- 0.27 mEq/l; P less than 0.001). Magnesium administration significantly lowered MBP over the 1-h infusion in the DOCA-salt (167 +/- 8 to 145 +/- 5 mmHg, P less than 0.001) but not the renovascular hypertensive rats (191 +/- 5 to 183 +/- 4, NS). We conclude that the blood pressure lowering effect of Mg is related, in part, to the state of activation of the renin-angiotensin system. The mechanism of this differential effect remains to be determined.     

Central administration of a specific angiotensin II receptor antagonist on baroreflex function in spontaneously hypertensive rats.

To determine whether the increase in baroreflex sensitivity previously reported in lifetime captopril-treated spontaneously hypertensive rats (SHR) was due to an inhibition of brain angiotensin II mechanisms, we tested the effect of intracerebroventricular administration of an angiotensin II receptor antagonist on baroreflex control of heart rate in lifetime captopril-treated and untreated male and female SHR. Baroreceptor reflex control of heart rate was assessed by the slope of the relationship between changes in mean arterial pressure (delta MAP, mmHg) and changes in pulse interval (delta PI, ms). MAP was raised and lowered with infusions of phenylephrine and nitroprusside, respectively. Following basal assessment of baroreflex control of heart rate, rats received an intracerebroventricular injection (100 pmol) of Sar1Thr8 angiotensin II (sarthran) and reflex control of heart rate was reassessed. Adequacy of blockade was tested with central and peripheral administration of angiotensin II. Captopril-treated male (130 +/- 7 mmHg) and female (123 +/- 4 mmHg) rats had significantly lower MAP than untreated rats (174 +/- 4 and 173 +/- 8 mmHg, respectively) and enhanced bradycardia in response to increases in MAP. Intracerebroventricular administration of sarthran had no effect on basal blood pressure or heart rate but enhanced the bradycardia in response to increases in MAP in both untreated and captopril-treated rats. The increase in the slope of the line relating delta MAP to delta PT was greater for untreated than captopril-treated SHR (male untreated 2.7-fold versus captopril-treated 1.5-fold; female untreated 1.6-fold versus captopril-treated 1.5-fold).(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of chloride in angiotensin II-induced salt-sensitive hypertension

The present study investigated the effect of the anion accompanying sodium on the development of angiotensin II-induced hypertension in rats and the role of the sympathetic nervous system and extracellular fluid volume in its mechanism. Hypertension was induced by intraperitoneal infusion of angiotensin II (125 ng/min) for 12 days via miniosmotic pump. High dietary intake of sodium chloride significantly augmented the angiotensin II-induced hypertension (mean blood pressure on day 13, 165 +/- 6 versus 142 +/- 6 mm Hg, p less than 0.05), but equimolar sodium loading provided as sodium citrate failed to enhance angiotensin II hypertension (140 +/- 6 mm Hg). Plasma norepinephrine concentration in the conscious, resting state increased with sodium chloride loading in angiotensin II-infused rats (594 +/- 42 versus 312 +/- 37 pg/ml, p less than 0.01), but it remained unchanged with sodium citrate loading (324 +/- 23 pg/ml). Correspondingly, maximum response to hexamethonium bromide, a ganglion blocker, was greater in sodium chloride-loaded angiotensin II rats (77.7 +/- 4.6 mm Hg) than that in angiotensin II (59.7 +/- 5.1 mm Hg) or in sodium citrate-loaded angiotensin II (57.7 +/- 4.2 mm Hg) rats. Moreover, extracellular fluid volume, measured as Na2(35)SO4 space, increased in sodium chloride-loaded angiotensin II rats (427 +/- 18 ml/kg body wt) as compared with that in angiotensin II rats (375 +/- 15 ml/kg body wt) but not when compared with volume in sodium citrate-loaded angiotensin II (389 +/- 7 ml/kg body wt) rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic kinin receptor blockade attenuates the antihypertensive effect of ramipril.

The contribution of endogenous kinins to the chronic antihypertensive effect of angiotensin converting enzyme inhibitors was investigated in two-kidney, one clip hypertensive Wistar rats, using the new bradykinin B2-receptor antagonist HOE 140 (D-Arg, [Hyp3, Thi5, D-Tic7, Oic8]-bradykinin). In a first protocol, rats were pretreated orally with the angiotensin converting enzyme inhibitor ramipril (1 mg/kg per day), for 4 weeks. Acute blockade of bradykinin receptors by intravenous injections of HOE 140 at doses of 8.4 and 100 micrograms/kg, which inhibited the depressor responses to exogenous bradykinin, did not affect the antihypertensive effect of ramipril in these animals. Bradykinin receptors were then blocked chronically by subcutaneous infusion of HOE 140 (500 micrograms/kg per day) via osmotic minipumps for 6 weeks, while ramipril treatment was continued. HOE 140 partially reversed the antihypertensive effect of ramipril from 115.3 +/- 4.6 to 123.8 +/- 3.3 mm Hg (mean arterial blood pressure) after 3 weeks and to 121.3 +/- 2.9 mm Hg after 6 weeks. In contrast, in controls (ramipril plus subcutaneous vehicle infusion) mean arterial blood pressure decreased further from 112.0 +/- 6.0 to 110.3 +/- 4.9 mm Hg after 3 weeks and to 103.7 +/- 5.0 mm Hg after 6 weeks (p less than 0.05 and p less than 0.01, HOE 140 versus controls). Plasma catecholamines were not significantly different between the two groups at the end of the experiment, indicating that the partial reversal of the antihypertensive effect was not due to a bradykinin-like agonistic effect on catecholamine release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of the antihypertensive effect of a thiazide diuretic in angiotensin II-induced hypertension

OBJECTIVES : The antihypertensive effect of thiazide diuretics in angiotensin II induced hypertension has never been characterized. In the current study, we sought to determine the effect of a thiazide diuretic on arterial pressure and renal fluid excretion in rats receiving a chronic intravenous infusion of angiotensin II while on fixed normal or high sodium intakes. DESIGN AND METHODS : Male rats were chronically instrumented with arterial and venous catheters for drug injection and direct daily measurements of blood pressure and heart rate. Rats were maintained on high salt intake (HS), 6 mEq/day, or on normal salt intake (NS), 2 mEq/day. Rats were randomly assigned to four groups: HS and NS with 15 day angiotensin II infusion (5 ng/min) and HS and NS without angiotensin II infusion. Trichlormethiazide (TCM), a thiazide diuretic, was orally administered, approximately 10 mg/kg per day, for the middle 5 days of angiotensin II infusion. RESULTS : Only HS rats receiving angiotensin II infusion became hypertensive. Angiotensin II infusion did not produce changes in heart rate, sodium balance or water balance. Chronic administration of TCM significantly reduced mean arterial pressure (MAP) within 24 h in HS rats receiving angiotensin II, but did not affect MAP in any other group. TCM produced a similar loss of Na+ and water in all rats. Blood volumes and plasma electrolytes did not change during the study. CONCLUSIONS : The antihypertensive effects of thiazide diuretics are not due exclusively to volume depletion. We propose that salt and water loss caused by TCM may lower MAP by impairment of salt-sensitive pressor mechanisms activated by angiotensin II.     

Effect of V1-vasopressin receptor blockade on arterial pressure in conscious rats with cirrhosis and ascites.

Angiotensin II blockade with saralasin in human cirrhosis with ascites is associated with a significant reduction in arterial pressure, indicating that endogenous angiotensin II plays an important role in the maintenance of systemic hemodynamics in this condition. The aim of the current study was to investigate whether vasopressin also contributes to the maintenance of arterial pressure in cirrhosis with ascites. The study was performed using three groups of cirrhotic rats with ascites and three groups of control animals. The administration of d(CH2)5Tyr(Me)AVP, a selective antagonist of the vascular effect of vasopressin, to 10 cirrhotic rats induced a significant reduction in mean arterial pressure (from 94 +/- 4 to 85 +/- 4 mm Hg; P less than 0.001) and a significant increase in plasma renin activity (from 24.3 +/- 4.9 to 34.3 +/- 5.9 ng/mL.h; P less than 0.02) and plasma norepinephrine concentration (from 1474 +/- 133 to 2433 +/- 253 pg/mL; P less than 0.01). Similar results were observed following saralasin administration in a second group of 5 cirrhotic rats [mean arterial pressure decreased from 97 +/- 4 to 85 +/- 5 mm Hg (P less than 0.0001); and plasma renin activity and norepinephrine concentration increased from 18.4 +/- 5.8 to 40.3 +/- 5.7 ng/mL.h (P less than 0.02) and from 1383 +/- 70 to 2312 +/- 334 pg/mL (P less than 0.05), respectively]. The simultaneous blockade of angiotensin II and vasopressin in a third group of cirrhotic rats resulted in a significantly greater reduction of mean arterial pressure (from 97 +/- 6 to 74 +/- 6 mm Hg; P less than 0.05). No changes in arterial pressure were observed in the three groups of control rats. These findings indicate that endogenous vasopressin is as important as angiotensin II in the maintenance of arterial pressure in cirrhotic rats with ascites and support the contention that arterial hypotension is the initial event leading to the stimulation of the renin-angiotensin system and vasopressin in this animal model of cirrhosis.     

Effects of a competitive antagonist of bradykinin on blood pressure and renal blood flow in anesthetized rats

To examine a possible role of endogenous bradykinin in the regulation of blood pressure (BP) and renal blood flow (RBF), a newly synthesized competitive antagonist of bradykinin (B4147) was studied in anesthetized rats. Also, the question of whether the hypotensive effect of the converting enzyme inhibitor, captopril, is mediated partly by an accumulation of endogenous bradykinin was considered. The intravenous infusion of B4147 (25 micrograms/min) inhibited the depressor effect of exogenous bradykinin (0.5 microgram, i.v.) by 69%. After an intravenous injection of B4147 at doses of 25, 50 and 100 micrograms, BP increased and RBF decreased in a dose-dependent fashion. The increase in BP was not blocked by pretreatment with an angiotensin II antagonist (1-Sar-8-Ile angiotensin II; 20 micrograms/kg per min) or an alpha 1-blocker (prazosin; 0.1 mg/kg). The administration of captopril (1 mg/kg) decreased mean BP from 110 +/- 3.5 to 71 +/- 1.9 mmHg (P less than 0.001). However, the injection of B4147 (50 micrograms) after the administration of captopril elicited an increase in BP of 43% of the initial decrease induced by captopril. These results suggest that the effects of B4147 on BP and RBF are not mediated through angiotensin II or sympathetic alpha 1-stimulation. Endogenous bradykinin could contribute to the maintenance of BP and RBF in anesthetized rats, probably counter-balancing the vasoconstrictor mechanisms. It is also suggested that bradykinin may partly participate in the acute hypotensive effect induced by the converting enzyme inhibitor captopril.     

Valsartan improves the lower limit of cerebral autoregulation in rats.

The effects of angiotensin II type 1 receptor blockers (ARBs) on cerebral blood flow (CBF) autoregulation have not been fully clarified. Thus, we examined the acute effect of valsartan, the most selective ARB, on CBF autoregulation in spontaneously hypertensive rats. Intravenous administration of valsartan (0.3 mg/kg) reduced the mean arterial pressure (MAP) from 184+/-5 (mean+/-SEM) to 174+/-5 mmHg (p<0.001) without affecting CBF as measured by laser-Doppler flowmetry. The lower limit of CBF autoregulation (the MAP at which the CBF was 80% of the baseline value) in the valsartan-treated group (122+/-3 mmHg) was significantly lower than that in the control group (135+/-4 mmHg, p<0.05). Reverse transcribed-polymerase chain reaction and immunohistochemical staining demonstrated that both angiotensin II type 2 receptors and angiotensin II type 1 receptors (AT1Rs) were expressed in endothelial and smooth muscle cells of the rat cerebral arteries. These results suggest that specific inhibition of AT1Rs in the cerebral circulation causes the leftward shift of the lower limit of autoregulation.     

Role of chymase-dependent angiotensin II formation in regulating blood pressure in spontaneously hypertensive rats.

Vascular smooth muscle cells in spontaneously hypertensive rats (SHR) express angiotensin II-forming chymase (rat vascular chymase [RVCH]), which may contribute to blood pressure regulation. In this study, we studied whether chymase-dependent angiotensin II formation contributes to the regulation of blood pressure in SHR. The systolic blood pressure in 16-week-old Wistar-Kyoto (WKY) rats was 113 +/- 9 mmHg, compared to 172 +/- 3 mmHg in SHR. Using synthetic substrates for measuring angiotensin-converting enzyme (ACE) and chymase activities, it was found that both ACE and chymase activities in extracts from SHR aortas were significantly higher than in those from WKY rat aortas. Using angiotensin I as a substrate, angiotensin II formation in SHR was found to be significantly higher than that in WKY rats, and its formation was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. RVCH mRNA expression could not be detected in aorta extracts from either WKY rats or SHR. In carotid arteries isolated from WKY rats and SHR, angiotensin I-induced vasoconstriction was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. Angiotensin I-induced pressor responses in both WKY rats and SHR were also completely inhibited by an ACE inhibitor, but they were not affected by a chymase inhibitor. In SHR, an ACE inhibitor and an angiotensin II receptor blocker showed equipotent hypotensive effects, but a chymase inhibitor did not have a hypotensive effect. These results indicated that chymase-dependent angiotensin II did not regulate blood pressure in SHR in the present study.     

α-Adrenergic Blocking Action of 1-O-Hexadecyl-2-0-Acetyl-sn-Glycero-3-Phosphocholine in Rats

The effect of 1-0-hexadecyl-2-0-acetyl-sn-glycero-3-phospho-choline (HAGPC), a major component of antihypertensive polar renomedullary lipid, on the pressor responses to norepinephrine and angiotensin II was investigated in normal Wistar rats. The pressor activity of norepinephrine (1 µg/kg of body weight (BW)) and angiotensin II (40 ng/kg BW) were markedly suppressed when these substances were injected immediately after intravenous administration of 80 nmol/kg BW of HAGPC. When HAGPC was infused continuously at a rate of 20 nmol/kg BW/min, pressor responses to bolus injection of graded doses (0.5 to 10 µg/kg BW) of norepinephrine were significantly lowered, but pressor responses to 10 to 200 ng/kg BW of angiotensin II were not affect-ed. These observations suggest that HAGPC has α-adrenergic blocking activity and does not influence angiotensin II receptors.     

A vaccine for hypertension based on virus-like particles: preclinical efficacy and phase I safety and immunogenicity

BACKGROUND: Despite the availability of efficacious drugs, the success of treating hypertension is limited by patients' inconsistent drug intake. Immunization against angiotensin II may offer a valuable alternative to conventional drugs for the treatment of hypertension, because vaccines induce relatively long-lasting effects and do not require daily dosing. Here we describe the preclinical development and the phase I clinical trial testing of a virus-like particle (VLP)-based antihypertensive vaccine. METHODS AND RESULTS: An angiotensin II-derived peptide was conjugated to the VLP Qbeta (AngQb). AngQb was highly immunogenic in mice and rats. To test for efficacy, spontaneously hypertensive rats (SHR) were immunized with 400 microg AngQb or VLP alone. Group mean systolic blood pressure (SBP) was reduced by up to 21 mmHg (159 +/- 2 versus 180 +/- 5 mmHg, P < 0.001), and total angiotensin II levels (antibody-bound and free) were increased ninefold (85 +/- 20 versus 9 +/- 1 pmol/l, P = 0.002) compared with VLP controls. SHR treated with the angiotensin-converting enzyme (ACE) inhibitor ramipril (1 mg/kg per day by mouth) reached an SBP of 155 +/- 2 mmHg. Twelve healthy volunteers of a placebo-controlled randomized phase I trial were injected once with 100 microg AngQb. Angiotensin II-specific antibodies were raised in all subjects (100% responder rate) and AngQb was well tolerated. CONCLUSIONS: AngQb reduces blood pressure in SHR to levels obtained with an ACE inhibitor, and is immunogenic and well tolerated in humans. Therefore, vaccination against angiotensin II has the potential to become a useful antihypertensive treatment providing long-lasting effects and improving patient compliance.     

Reduced glomerular angiotensin II receptor density in diabetes mellitus in the rat: time course and mechanism

Glomerular angiotensin II receptors are reduced in number in early diabetes mellitus, which may contribute to hyperfiltration and glomerular injury. The time course and role of the renin-angiotensin-aldosterone system in the pathogenesis of the receptor abnormality were studied in male Sprague-Dawley rats made diabetic with streptozotocin (65 mg, iv). Glomerular angiotensin II receptors were measured by Scatchard analysis; insulin, renin activity, angiotensin II, and aldosterone were measured by RIA. Diabetes mellitus was documented at 24 h by a rise in plasma glucose (vehicle-injected control, 133 +/- 4; diabetic, 482 +/- 22 mg/dl; P less than 0.001) and a fall in plasma insulin (control, 53.1 +/- 5.7; diabetic, 35.6 +/- 4.0 microIU/ml; P less than 0.05). At 24 h glomerular angiotensin II receptor density was decreased by 26.5% in diabetic rats (control, 75.5 +/- 9.6 X 10(6); diabetic, 55.5 +/- 8.3 X 10(6) receptors/glomerulus; P less than 0.01). Receptor occupancy could not explain the defect, because there was reduced binding in diabetic glomeruli after pretreatment with 3 M MgCl2, a maneuver that caused dissociation of previously bound hormone. There was a progressive return of the receptor density toward normal over the 60 days following induction of diabetes, with diabetic glomeruli measuring 22.7%, 14.8%, and 3.7% fewer receptors than age-matched controls at 11 days, 1 month, and 2 months, respectively (r = 0.99; n = 4; P less than 0.01). Three lines of evidence suggested that reduced angiotensin II receptor density at 24 h was not due to down-regulation by angiotensin II: PRA and angiotensin II were identical in control and diabetic rats; angiotensin II infusion (50 ng/min) caused down-regulation in both control and diabetic rats, but the change in receptor density persisted (control, 33.6 +/- 6.9 X 10(6); diabetic, 18.5 +/- 1.3 X 10(6) receptors/glomerulus; P less than 0.05); and angiotensin-converting enzyme inhibition with enalapril caused receptor up-regulation, but the differences persisted (control, 105.5 +/- 21.2 X 10(6); diabetic, 67.1 +/- 3.0 X 10(6) receptors/glomerulus; P less than 0.05). Rats with chronic diabetes (7-60 days) had normal PRA and angiotensin II, but plasma aldosterone was elevated (control, 29.8 +/- 3.3; diabetic, 68.6 +/- 12.4 ng/dl; P less than 0.005). The return of angiotensin II receptor density to normal levels in chronic diabetes may be the result of receptor up-regulation by increased plasma aldosterone rather than recovery of the underlying defect.     

Prolonged angiotensin II antagonism in spontaneously hypertensive rats. Hemodynamic and biochemical consequences

The present study examines the effects of prolonged angiotensin II antagonism in spontaneously hypertensive rats by using an angiotensin II receptor antagonist (DuP 753) that is devoid of agonistic properties and selective for the subtype 1 of the angiotensin II (AT1) receptor. The antihypertensive effects of DuP 753 and its effects on circulating parameters of the renin-angiotensin system were compared with those of a converting enzyme inhibitor (benazeprilat). To minimize any influence of differences in the pharmacokinetic properties of the two blockers, administration was by continuous intravenous infusion. The experiments were performed in conscious, freely moving rats with continuous 24-hour monitoring of blood pressure. DuP 753 (10 or 30 mg/kg/day) lowered mean arterial pressure to the same extent as benazeprilat (3 or 10 mg/kg/day) during a 48-hour period. The antihypertensive effect was sustained when the treatment was extended to 7 days (DuP 753, 10 mg/kg/day; benazeprilat, 3 mg/kg/day). Neither of the compounds affected the baseline or diurnal rhythm of heart rate. Plasma concentrations of renin and angiotensin II were increased sevenfold and 10-fold, respectively, in the rats treated with DuP 753. In rats treated with benazeprilat, plasma renin concentration increased threefold, whereas angiotensin II was unchanged. Heart weights were significantly reduced to a similar extent by DuP 753 and benazeprilat. Both compounds also induced a smaller but significant decrease in blood pressure in Wistar-Kyoto rats. Our results indicate that the antihypertensive effects of converting enzyme inhibitors in spontaneously hypertensive rats are mainly due to the blockade of the renin-angiotensin system. In this rat model, angiotensin II appears to play an important role in the maintenance of hypertension that is mediated via the AT1 receptor.     

Immunocytochemical and biochemical characterization of angiotensin I and II in cultured neuronal and glial cells from rat brain

Neuronal and glial cells cultured from neonatal rat brains showed staining for both angiotensin I and II using the peroxidase-antiperoxidase method. In glial cell extracts of normotensive Wistar-Kyoto rats, the concentrations of angiotensin I and II were 12.47 +/- 2.71 (n = 4) and 66.73 +/- 13.28 fmol/mg protein (n = 4). Angiotensin I and II found in neuronal cell extracts of normotensive Wistar-Kyoto rats were 11.29 +/- 2.99 (n = 4) and 60.25 +/- 12.77 fmol/mg protein (n = 4). No significant difference was found in the concentration of angiotensin I and II in both cell types from the same rat strain. Angiotensin I concentrations of 16.83 +/- 3.43 fmol/mg protein (n = 5) determined in neuronal cell extracts derived from spontaneously hypertensive rats did not differ significantly from those found in neuronal cell extracts of Wistar-Kyoto rats. However, neuronal cell extracts from spontaneously hypertensive rats revealed values of 25.19 +/- 4.31 fmol angiotensin II/mg protein (n = 4). This was significantly different (p less than 0.05) and represented a 58% reduction in the angiotensin II levels in neuronal cells from spontaneously hypertensive rats compared to Wistar-Kyoto rat cultures. Angiotensin I and II measured in the growth medium containing 10% plasma-derived horse serum was below the detection limit of both radioimmunoassays. No difference in the angiotensin I and II levels was found in cells kept in serum-free medium. The angiotensin I and II immunoreactive material determined in the cell extracts could be characterized on reversed-phase high pressure liquid chromatography as (Ile5)-angiotensin I and II. (Ile5)-angiotensin III was not detectable.     

Effect of a kinin antagonist on the acute antihypertensive activity of enalaprilat in severe hypertension

The purpose of this study was to assess the role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor (CEI) enalaprilat in rats with severe hypertension induced by aortic ligation between both renal arteries. For this study, we used a bradykinin analogue, D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-DPhe-Thi-Arg-TFA, with in vivo antagonistic properties. Hypertensive rats were infused intra-aortically for 15 minutes with either saline (30 microliters/min) or the kinin antagonist (40 micrograms/kg/min). Five minutes after the infusion was begun, a bolus injection of enalaprilat (60 micrograms/kg) was given. The blood pressure of the saline-infused animals decreased 48 +/- 6 mm Hg (from 180 +/- 7 to 132 +/- 7 mm Hg), while that of the rats treated with the antagonist decreased only 21 +/- 4 mm Hg (from 175 +/- 3 to 154 +/- 3 mm Hg). The difference between both decrements was significant (p less than 0.01). In another group of hypertensive animals (n = 9), we measured kinin concentration in plasma from arterial blood before and after administration of CEI (41 +/- 10 vs 68 +/- 20 pg/ml, respectively; NS). These results are consistent with the hypothesis that kinins play a role in the acute antihypertensive effect of CEIs in rats with severe hypertension. However, since arterial blood kinin concentrations were not increased significantly after CEI administration, the effect of the CEI may be due to an increase in tissue kinins, which could act as autacoids regulating vascular resistance.