Converting Enzyme Inhibition in Mild and Moderate Essential Hypertension: I. Acute Effects on Blood Pressure,the Renin-Angiotensin System and Blood Bradykinin after a Single Dose of Captopril

ABSTRACT. The acute effects of 25 mg captopril on blood pressure, heart rate, components of the renin-angiotensin system and blood concentration of bradykinin were followed in a single-blind placebo study of untreated (group A, n = 15) and thiazide-treated (group B, n = 13) patients with mild or moderate essential hypertension. A drug-related fall in blood pressure was seen in both groups. The blood pressure reduction was more marked in group B than in group A. Heart rate remained unchanged. Plasma concentrations of angiotensin II decreased significantly with concurrent increases in plasma concentrations of renin and angiotensin I, indicating the in vivo inhibition of converting enzyme. Blood concentrations of bradykinin showed no systemic changes. The magnitude of blood pressure reduction was correlated both with the pretreatment levels and the concurrent decreases in plasma angiotensin II. Inhibition of angiotensin II formation can explain a large part of the acute hypotensive pharmacological action of captopril. Other vasoactive systems may be involved. The kallikrein-kinin system does not appear to participate as indicated by the unchanged concentrations of kinin in blood.     

Use of Captopril in the Diagnosis of Renal Hypertension

Abstract: 1 . The effects of a single 25 mg oral dose of captopril on blood pressure, heart rate and circulating renin, angiotensin I, angiotensin II, bradykinin and catecholamine levels were examined in untreated patients with essential (n = 10, Group I), accelerated (n = 6, Group II) and renal hypertension (n = 8, Group III) studied on a normal sodium diet .
2 . Mean blood pressure fell only slightly in Group I patients, (113 ± 3 to 109 ± 3 mmHg at 60 minutes) but a greater fall was observed in Group II (153 ± 8 to 135 ± 11 mmHg) and a marked fall in Group III, (136 ± 3 to 114 ± 5 mmHg). There were no significant changes in heart rate in any group .
3 . Plasma angiotensin II levels were significantly reduced 30 minutes after captopril in all three groups and returned toward resting values after four hours. The falls in plasma angiotensin II levels were accompanied by reciprocal increases in blood angiotensin I and plasma renin, but blood bradykinin and plasma catecholamine concentrations remained unchanged .
4 . Resting plasma renin levels showed considerable overlap in the three groups and the mean renin values were not significantly different in the three groups. After captopril a marked rise in plasma renin concentration (>2.5 ng/ml/hr) was observed in seven patients in Group III, including all six patients with renovascular disease. In contrast, none of the patients with essential hypertension and only one patient with accelerated hypertension had such an increase. Determination of the acute renin and blood pressure responses to converting enzyme inhibition with a single oral dose of captopril appears to be useful in identifying patients with renovascular hypertension .     

Converting Enzyme Inhibition in Mild and Moderate Essential Hypertension. II

ABSTRACT. In 24 patients with mild/moderate essential hypertension, we studied the effects of captopril with/without hydrochlorothiazide (Htz) on blood pressure, the renin-angiotensin system, blood bradykinin concentration (BBK), plasma volume, exchangeable sodium and glomerular filtration. Daily captopril doses of 75 and 150 mg were equally effective in reducing the blood pressure. Addition of Htz caused further blood pressure reductions. Nineteen patients attained a diastolic blood pressure ≤90 mmHg. Angiotensin converting enzyme inhibition with captopril led to a fall in plasma concentrations of angiotensin II (PAII) and renin substrate, and an increase in plasma concentrations of renin and angiotensin I. Patients starting with Htz had a higher PAII and subsequently a larger fall in blood pressure on captopril than untreated patients. BBK remained unchanged, indicating that the hypotensive action of captopril does not involve an accumulation of circulating kinin. Body fluid volumes and renal function were not affected by the various treatment regimens.     

Evidence for the role of kinins in the acute antihypertensive effect of captopril in low-renin hypertension

In low-renin hypertensive patients, the acute effect of the angiotensin I-converting enzyme inhibitor, captopril, was evaluated in relation to the response of plasma bradykinin (PBK) levels as a parameter of its inhibitory effect on kininase II. Captopril significantly lowered the blood pressure and increased PBK levels. While there was no significant relationship between the reduction of blood pressure and pretreatment plasma renin activity, a significant correlation was observed between the antihypertensive effect of captopril and changes in PBK (r = -0.834, p less than 0.01, n = 10). Furthermore, in a patient with primary aldosteronism and, also, in a patient with glucocorticoid responsive hyperaldosteronism, captopril increased plasma PBK with reduction of the blood pressure. It is likely, therefore, that in low-renin hypertension, the vasodepressor effect of acute converting enzyme inhibition is due mainly to kinin accumulation rather than inhibition of angiotensin II formation.     

Responses of plasma bradykinin and the renin angiotensin axis to angiotensin II in hyperthyroid patients

The present investigation was undertaken to elucidate the possible interplay between the circulating kinin(s) and the renin angiotensin axis in hyperthyroidism. The responsiveness of plasma aldosterone (p-Ald), kinin (p-BK), plasma renin activity (PRA) and serum angiotensin converting enzyme activity (ACEA) to infusion of angiotensin II at a dose of 4, 8 and 16 ng/kg.min. was asessed in 15 hyperthyroid patients and 10 euthyroid controls. There was impaired angiotensin II induced response of blood pressure in hyperthyroid patients, and basal concentrations of p-Ald were 7.7 +/- 3.8 ng/dl in euthyroid controls and 12.6 +/- 3.1 ng/dl in hyperthyroid patients (p less than 0.05). As compared to the euthyroid controls, the hyperthyroid patients showed a reduced response of plasma aldosterone to angiotensin II infusion. Angiotensin II infusion increased p-BK from basal levels of 19.1 +/- 8.2 pg/ml to 31.0 +/- 7.8 pg/ml (p less than 0.05) only in hyperthyroid patients and did not increase ACEA in either group. Next, the effects of a single administration of captopril (50 mg p.o.) on blood pressure and p-BK in hyperthyroid patients and euthyroid controls were studied. In the two groups blood pressure was not changed by captopril, but p-BK increased significantly. The present results do not support the view that there may be a direct linkage between the kallikrein kinin system and the renin angiotensin axis mediated by kininase II or angiotensin converting enzyme in human peripheral blood. Also it is unlikely that kinin may play a role in the mechanism of reduced responsiveness of aldosterone and blood pressure to angiotensin II in hyperthyroidism.     

Bradykinin May Not Be Involved in Improvement of Insulin Resistance by Angiotensin Converting Enzyme Inhibitor

We have previously demonstrated that captopril ameliorates glucose intolerance by partially preventing the reduction in postprandial skeletal muscle blood flow. The present study was designed to clarify the mechanism by which ACE inhibitors affect glucose metabolism in fructose (FRU)-fed Wistar rats with hypertension, glucose intolerance and hyperinsulinermia. Eight-week-old male rats (n=51) were divided into six groups. Controls were given a normal chow, while fructose-rich (55%) chow was administered to the remainder for eight weeks. The different groups were administered alacepril (ALA, 30 mg/kg/day) with or without a continuous infusion of Hoe 140, a kinin B₂ receptor antagonist (150 μ/kg/day), Hoe 140 alone or TCV-116 (1 mg/kg/day), an angiotensin II receptor antagonist, alone. After measuring the body weight and systolic bolld pressure (BP), steady-state plasma glucose (SSPG) levels were determined. FRU significantly increased BP from 141 mmHg in controls to 156 mmHg. ALA with or without Hoe 140 decreased BP to 124 mmHg or 117 mmHg, respectively, but Hoe 140 alone did not affect BP. TCV-116 also decreased BP to 11 6 mmHg. The SSPG levels increased from 7.58 mM in controls to 8.98 mM in FRU-fed rats. This was lowered with both ALA and TCV-116. Hoe 140 alone, however, did not affect SSPG levels. Hoe 140 did not show any effects on ALA-induced improvement of SSPG. These results suggest that the improvement in glucose tolerance observed with ACE inhibitors is not due to the kinins, and angiotensin II receptor antagonists also improve insulin sensitivity.     

Hemodynamic and neurohumoral effects of moxonidine in patients with essential hypertension

Summary The hemodynamic and neurohumoral effects of a single oral dose (0.4 mg) of the novel centrally acting antihypertensive agent moxonidine were investigated over 4 hours in ten patients with essential hypertension (WHO I-II). Pulmonary pressure indices and cardiac output were determined both at rest and during ergometric exercise by means of Swan-Ganz catheterization. Blood pressure was measured by sphygmomanometry and in the brachial artery. Moxonidine induced a significant fall in blood pressure over the 4-hour observation period from 176/105 mmHg to 158/95 mmHg (p<0.01), accompanied by a decrease in systemic vascular resistance from 1695 to 1427 dyn.sec/cm⁵ (p<0.01). Cardiac output remained unchanged, while heart rate increased slightly from 69 to 75 beats/min (p<0.01). No significant changes were recorded for either pulmonary artery pressure or pulmonary vascular resistance. Plasma levels of noradrenaline (337 vs. 224 pg/ml) and renin (2.6 vs 2.0 ng/ml/hr) activity fell significantly after moxonidine (p<0.05), both at rest and during exercise. Although aldosterone plasma levels fell slightly, levels of angiotensin II and ANF remained unchanged.Moxonidine has favorable effects on hemodynamics and the neurohumoral system in patients with essential hypertension and is well tolerated at the dose administered.     

老年原发性高血压患者动态血压参数与部分体液因素的相关性研究

目的观察老年原发性高血压患者动态血压参数与血浆肾素、血管紧张素Ⅱ及醛固酮的相关性及其临床意义。方法将162例患者分为A纽82例（〉60岁）,B组80例（〈60岁）,采用放射免疫法检测162例原发性高血压患者的血浆肾素、血管紧张素Ⅱ及醛固酮水平,同时测定24h动态血压,进行相关分析。结果（1）老年高血压具有是脉压增大,波动性大,晨峰高血压现象及并发症多的特点;（2）A组血浆肾素、血管紧张素Ⅱ及醛固酮水平明显高于B组;（3）血浆肾素、血管紧张素Ⅱ及醛固酮与老年高血压的特点,特别是脉压增大、波动性大、晨峰高血压现象有关。结论老年原发性高血压患者血浆肾素和血管紧张素Ⅱ浓度升高,提示血浆肾素、血管紧张素一醛固酮系统对老年原发性高血压心血管系统有影响,导致老年原发性高血压患者血压特征性的变化,血浆肾素、血管紧张素Ⅱ和醛固酮的测定可作为老年原发性高血压患者病情监测及治疗指标之一。     

The metabolic clearance of aldosterone decreases similarly during infusion of angiotensin II in patients with essential hypertension and in normal subjects.

To determine if the abnormally large increases in levels of plasma aldosterone which occur during infusion of angiotensin II in some patients with essential hypertension are due to abnormal decreases in the metabolic clearance of aldosterone, we measured clearances of aldosterone before and during infusion of angiotensin II in 12 patients with essential hypertension and in 10 normal subjects. The metabolic clearance of aldosterone in the patients and that in the normal subjects were the same before angiotensin II was infused and the clearances decreased similarly during infusion of angiotensin II. In agreement with our previous observations, the plasma aldosterone responses to angiotensin II were greater than normal in most of the patients with low renin essential hypertension. Thus, the brisk increases in levels of plasma aldosterone during infusion of angiotensin II in patients with essential hypertension reflect abnormally large increases in the secretion of aldosterone. These results add further support to the idea that adrenal sensitivity to angiotensin II is increased in some patients with essential hypertension.     

Endogenous angiotensin-aldosterone-pressure relationships during sodium restriction

The effects of moderate restriction of dietary sodium and potassium supplementation on plasma levels of renin, angiotensin II, aldosterone, and cortisol and on arterial pressure were studied in 12 patients with mild essential hypertension. To define hormone-blood pressure relationships, venous hormone levels were measured hourly and intra-arterial pressure continuously for 24 hours after 4 to 6 weeks of sodium restriction, 4 to 6 weeks of potassium supplementation, and a similar period of control diet. Our results show that compared with the control diet, moderate sodium restriction was associated with increased levels of aldosterone but no overall change in renin, angiotensin II, or cortisol levels. Further, slopes of regression lines relating log renin and log angiotensin II to aldosterone were increased, as were log cortisol/aldosterone regression lines. On the contrary, regression lines of log renin and log angiotensin II versus arterial pressure were unaltered by sodium restriction. Hormone and blood pressure relationships were not changed by the potassium supplemented diet. Although confirmatory data are needed, our findings suggest that moderate sodium restriction enhances aldosterone responsiveness to endogenous angiotensin II and adrenocorticotropic hormone without diminishing the pressor activity of endogenous angiotensin II. These results may explain in part the disappointingly small hypotensive effect of modest sodium restriction in mild essential hypertension.     

不同血压人群ATⅠ、ATⅡ、肾上腺髓质素的水平比较

目的通过测定理想血压、血压正常高值及原发性高血压人群的血浆血管紧张素Ⅰ（ATⅠ）、血管紧张素Ⅱ（ATⅡ）和肾上腺髓质素（ADM）的水平,了解血压与血浆ATⅠ、ATⅡ及ADM水平的关系。方法分别纳入健康志愿者（理想血压组）40例、正常高值血压者（高值组）40例和原发性高血压（高血压组）患者30例,采用放射免疫法检测血浆ATⅠ、ATⅡ和ADM水平。结果三组间ATⅠ无统计学差异（P〉0.05）;与理想血压组相比,高值组和高血压组ATⅡ和ADM均较高（P〈0.05）,尤其以高血压组升高更为明显（P〈0.01）。结论 ATⅠ与血压无关ATⅡ和ADM随血压升高而水平呈上升趋势。     

Failure of renin suppression by angiotensin II in hypertension

Angiotensin II was infused at rates varying from 0.1 to 10 ng/kg per minute into 49 subjects with hypertension and 26 normotensive subjects and changes in blood pressure, plasma angiotensin II, and plasma renin activity (PRA) were determined after 20 and 30 minutes at each dose. Similar dose-related increases in angiotensin II and blood pressure occurred with a threshold of 1 ng/kg per minute in the normotensive and hypertensive subjects. Whereas angiotensin II induced a significant, dose-related decrement in renin activity in the normotensive subjects, with a threshold of 1.0 ng/kg per minute, no significant change in renin activity occurred in either the normal-renin or high-renin hypertensive subjects. In a separate study, nine normotensive and six hypertensive sodium-restricted subjects were given a converting enzyme inhibitor, SQ 20881, 30 microgram/kg. Despite a significantly greater fall in blood pressure (P less than 0.006) and angiotensin II concentration (P less than 0.045) in the hypertensive subjects, they did not have a greater rise in plasma renin activity. We conclude that angiotensin II reduces renin release in normal man at infusion rates that yield plasma angiotensin II levels within the physiological range but has a strikingly reduced influence on renin release in hypertension. In high-renin hypertension due to renal artery stenosis or nephrosclerosis, renin release is presumed to be relatively autonomous because of a dominant, intrarenal mechanism. The mechanism in normal-renin essential hypertension is not clear, but the abnormality could well be related to the pathogenesis of the hypertension.     

Angiotensin II Antagonists

Acute blockade of the renin-angiotensin system with the parenterally active angiotensin II antagonist saralasin has been shown to effectively lower blood pressure in a large fraction of patients with essential hypertension and to improve hemodynamics in some patients with congestive heart failure. It is now possible to antagonize chronically angiotensin II at its receptor using the non-peptide angiotensin I1 inhibitor losartan (DuP 753, MK 954). When administered by mouth, this compound induces a dose-dependent inhibition of the pressor response to exogenous angiotensin 11. This effect is closely related to circulating levels of the active metabolite E3174. Preliminary studies performed in hypertensive patients suggest that losartan has a blood pressure lowering action equivalent to that of an ACE inhibitor. Whether this compound will compare favorably with ACE inhibitors requires however further investigation.     

Relationships between blood pressure, heart rate and plasma epinephrine, norepinephrine, angiotensin II concentrations, plasma renin activity during chronic guanfacine therapy in patients with essential arterial hypertension

The evolution of blood pressure, heart rate, epinephrine, norepinephrine, angiotensin II and plasma renin activity has been studied in 10 patients with essential arterial hypertension before and during a two months period of treatment with guanfacine, a new centrally acting hypotensive drug. Guanfacine was proven effective in lowering both systolic and diastolic supine and standing blood pressure. A decrease in supine and standing norepinephrine plasma concentrations and plasma renin activity was observed. No change was seen in epinephrine or angiotensin II. The fall in supine blood pressure observed during the treatment period was positively correlated with the change in norepinephrine.     

Vascular,hemodynamic and renal effects of low‐dose losartan in rats with secondary biliary cirrhosis

Background: In cirrhosis, splanchnic and systemic vasodilatation induce a hyperdynamic circulatory dysfunction, portal hypertension and renal sodium retention. This vasodilatation is in part because of an impaired vascular response to α1‐adrenoceptor agonists. Recently, the angiotensin II type 1‐receptor antagonist losartan has been shown to attenuate portal hypertension. We hypothesized that losartan decreases portal pressure by counteracting the impaired vascular responsive to α1‐adrenoceptor agonists. Methods: We studied, in rats with secondary biliary cirrhosis and sham‐operated rats, the effect of 0.5 and 10 mg losartan/kg × day on aortic responsiveness to α1‐adrenoceptor stimulation with methoxamine and angiotensin II (myograph), splanchnic and systemic hemodynamics (colored microspheres), plasma noradrenaline levels and kidney function. Results: In cirrhotic rats, 10 mg losartan/kg × day completely inhibited aortic contractility to angiotensin II, decreased vascular resistance and arterial pressure and induced renal failure. In contrast, 0.5 mg losartan/kg × day only partially inhibited aortic contractility to angiotensin II, but improved aortic contractility to methoxamine, increased splanchnic and systemic vascular resistance, decreased portal pressure, decreased plasma norepinephrine levels and induced natriuresis. Conclusions: In cirrhotic rats, losartan at a very low dose increases splanchnic vascular resistance, decreases portal pressure and improves kidney function, possibly by an increased vascular responsiveness to α1‐adrenoceptor agonists.     

醛固酮合酶基因多态性与高血压患者血压及RAAS激素水平的相关性研究

目的探讨醛固酮合酶(CYP11B2)基因-344C/T多态性与高血压患者血压及肾素-血管紧张素-醛固酮系统(RAAS)激素水平的相关性。方法用放射免疫法检测171例原发性高血压患者(92例男性,79女性)RAAS激素水平,包括血浆肾素活性(PRA)、血浆血管紧张素II(AT-II)和醛固酮(ALD)水平。用聚合酶链反应(PCR)和限制性酶切方法检测所有患者的CYP11B2基因-344C/T多态性,按CC、CT和TT三种基因型分组。分析其与高血压患者血压及RAAS激素水平的相关性。结果 CYP11B2基因-344C/T多态性与高血压患者血压及血浆PRA和AT-II水平无关,但与血浆ALD水平相关,TT和CT基因型者的血浆ALD水平要高于CC基因型者,其差异有统计学意义(0.66±0.36or0.61±0.35versus0.42±0.23nmol/L,P=0.036)。结论本研究显示,高血压患者的CYP11B2基因-344C/T多态性与血浆ALD水平相关,提示该多态性可能参与了高血压患者血浆ALD水平的调节。     

Angiotensin-converting enzyme inhibition and prostaglandins

To determine whether prostaglandins contribute to the depressor response of angiotensin-converting enzyme inhibitors, plasma prostaglandin levels were measured by radioimmunoassay in normo- and hypertensive subjects on both sodium-restricted and sodium-loaded diets before and after captopril administration. On the sodium-restricted diet, the hypotensive response to captopril was accompanied by significant increments in the metabolite of prostaglandin E2 (PGE2-M) and bradykinin and by significant decrements in angiotensin II. The high sodium diet suppressed the response of the renin-angiotensin and kinin systems to captopril but the hypotensive response persisted. Furthermore, the decrease in blood pressure correlated significantly with increments in prostaglandin E2-metabolite. Prostaglandin synthesis was then inhibited in the sodium-restricted hypertensive patients by pretreatment with indomethacin. This maneuver completely eliminated the captopril-induced prostaglandin E2-metabolite increment without changing bradykinin or angiotensin II responses but significantly attenuating the hypotensive response. Finally, when patients were studied on a high sodium intake, similar effects were observed except now indomethacin completely abolished the blood pressure response to captopril. These studies therefore support the hypothesis that increased production of vasodilator prostaglandins in a major mediator of the hypotensive response to captopril. Whether the change in prostaglandin release is a direct effect of the drug or secondary to increased kinin levels is uncertain.     

Effects of captopril on the renin angiotensin system, oxidative stress, and endothelin in normal and hypertensive rats

There is substantial evidence suggesting that angiotensin II plays an important role in elevating blood pressure of spontaneously hypertensive rats, despite normal plasma renin activity, and that converting enzyme inhibitors (captopril) can effectively normalize blood pressure in the spontaneously hypertensive rats. One mechanism by which angiotensin II induces hypertension is via oxidative stress and endothelin, as seen in subpressor angiotensin II-induced hypertension. In fact, it has been shown that antioxidants lower mean arterial pressure in spontaneously hypertensive rats. However, the relationship between angiotensin II, oxidative stress, and endothelin in the spontaneously hypertensive rats is still relatively undefined. This study examines the relationship between mean arterial pressure, plasma renin activity, angiotensin II, oxidative stress, and endothelin in spontaneously hypertensive rats compared with normotensive Wistar Kyoto rats, and the effects of captopril on this association. Untreated spontaneously hypertensive rats had increased plasma angiotensin II levels despite normal plasma renin activity, oxidative stress, and endothelin. Captopril treatment in spontaneously hypertensive rats lowered mean arterial pressure, angiotensin II, oxidative stress, and endothelin, and increased plasma renin activity. In contrast, captopril increased plasma renin activity (suggesting effective captopril treatment) but did not significantly alter mean arterial pressure, angiotensin II, oxidative stress, or endothelin of Wistar Kyoto rats. These results suggest that in spontaneously hypertensive rats, angiotensin II is a primary instigator of hypertension, and that captopril selectively lowers angiotensin II, oxidant stress, and endothelin, which in turn may contribute to the blood pressure-lowering efficacy of captopril in spontaneously hypertensive rats.     

Enhanced adrenal responsiveness to angiotensin II in patients with low renin essential hypertension.

The plasma aldosterone response to infused angiotensin II was determined in normal controls and in patients with normal renin and with low renin essential hypertension. The patients with low renin essential hypertension showed an enhanced plasma aldosterone response when compared to the other two groups. This finding may explain why plasma aldosterone levels remain within normal limits in the face of suppressed plasma renin and angiotensin II concentrations in low renin essential hypertension.     

Sodium and responses to infused noradrenaline and angiotensin II in subjects predisposed to hypertension

A disturbed adrenergic dependent blood pressure regulation may represent a familial component in the pathogenesis of essential hypertension; its possible relation to sodium metabolism is presently unknown. Body sodium, the cardiovascular pressor reactivity to infused noradrenaline or angiotensin II, plasma levels of noradrenaline, adrenalin, renin, angiotensin II, aldosterone and atrial natriuretic peptide were measured on a low or high sodium diet in 10 normotensive young subjects without and 13 normotensive subjects with familial predisposition to hypertension. On the low sodium diet, the two groups did not differ significantly in the considered parameters, while blood pressure was slightly higher in predisposed subjects (+7/+7 mmHg). The change from the low to the high sodium diet was associated with a significant increase in supine systolic blood pressure in predisposed but not in non-predisposed subjects (P less than 0.05). Exchangeable sodium, body weight atrial natriuretic peptide and the pressor reactivity to infused adrenalin or angiotensin II increased significantly while plasma catecholamines, renin, angiotensin II and aldosterone levels were suppressed to a comparable extent in the two groups. The findings of this investigation confirm that sodium has an important regulatory effect on cardiovascular pressor responsiveness. The disturbed noradrenergic-dependent regulation of predisposed subjects is not explained by an abnormal adaptation of sympathetic dependent mechanisms or of other pressor factors to variations in dietary sodium intake.