Angiotensin II in essential hypertension

Renal transplantation increases angiotensin II receptor-mediated vascular contractility associated with changes of epigenetic mechanisms

Hypertension is one of the most common complications following renal transplantation, and it increases the risk of graft loss and other cardiovascular diseases. Previous studies have revealed that the use of angiotensin II (Ang II) blockers for preventing and treating hypertension is closely associated with higher survival following renal transplantation. However, the cellular and molecular mechanisms by which the vascular contractility of the recipient is altered in response to Ang II following renal transplantation have not been fully elucidated. In the present study, using the Fisher‑Lewis rat kidney transplantation model, the blood pressure (BP) of the conscious transplant recipient was measured following the intravenous administration of Ang II. In addition, the mechanisms underlying the Ang II-mediated vascular contractility via the type 1 and type 2 Ang II receptors (AT1R and AT2R, respectively) in large and small-resistance blood vessels were determined in the recipient after renal transplantation. The results showed that renal transplantation significantly increased the Ang II-stimulated BP of the rats. Additionally, ex vivo contractility experiments using aorta and mesenteric arteries revealed that the contractions induced by Ang II were significantly strengthened in the recipient following renal transplantation, and were associated with an increased intracellular Ca2+ concentration. Losartan almost eradicated the Ang II-induced contractions whereas PD-123319 had no apparent effects on the Ang II-induced contractions in the aorta and mesenteric arteries of the recipient. Furthermore, the expression levels of AT1R but not AT2R were significantly increased in the vasculature of the recipient following renal transplantation, which exhibited a close association with selective DNA demethylation detected in the promoter region of the vascular AT1aR gene. These results indicate that changes of recipient vascular AT1R gene expression, occurring through a mechanism involving DNA methylation, increase the vascular contractility in response to Ang II. This may lead to the increased risk of hypertension following renal transplantation.

Blood pressure in relation to the renin-angiotensin-aldosterone system

The relationship between blood pressure (BP) and the renin-angiotensin-aldosterone system was studied in a stratified random sample (n=120) of 49-year-old men selected from a BP screening and covering a wide range of BPs. Only subjects not on antihypertensive treatment were included. None had malignant or secondary hypertension. Plasma renin activity, plasma concentrations of angiotensin II, aldosterone, sodium, potassium and noradrenaline and the 24-hour urinary excretions of sodium, cortisol and noradrenaline were determined. Of these variables, only p-aldosterone was significantly correlated wtih BP, both in the whole study group (R=0.22, p less than 0.02, n=119) and in the subjects with the highest BP range (R=0.36, p less than 0.02, n=30). Of the clinical groups compared, the hypertensive subjects had significantly higher mean p-aldosterone than the borderline and normotensive subjects. Multiple regression analysis showed that the 24-hour urinary excretion of noradrenaline was the factor most strongly correlated to p-aldosterone, suggesting that the sympathetic nervous system might stimulate aldosterone secretion. Our findings indicate that aldosterone may be of importance for the development and maintenance of essential hypertension.

Captopril or atenolol in essential hypertension

Twenty-five patients with essential hypertension were randomly assigned to treatment with either captopril or atenolol. There were 15 males and 10 females and their mean age was 53 years, range 32-66 years. Systolic and diastolic blood pressures were significantly reduced by atenolol 50-100 mg once daily. Captopril 25-50 mg 3 times daily caused a significant decrease in supine diastolic but not in systolic blood pressure. After the addition of hydrochlorothiazide (25-50 mg) to those who did not become normotensive (supine diastolic blood pressure less than 95 mm Hg) on captopril or atenolol alone, blood pressure was further reduced. Captopril combined with hydrochlorothiazide significantly reduced both supine and standing blood pressure by 31/17 mm Hg (p less than 0.01) and 33/18 mm Hg (p less than 0.001) respectively. Atenolol combined with hydrochlorothiazide caused a significant decrease of both recumbent and standing blood pressure by 21/10 mm Hg (p less than 0.01) and 23/13 mm Hg (p less than 0.05 systolic, p less than 0.001 diastolic). The reduction of systolic blood pressure was significantly better with the captopril/hydrochlorothiazide combination, while there was no difference between the groups as regards diastolic blood pressure reduction. Thus, hydrochlorothiazide potentiates the blood pressure lowering effect of captopril more than of atenolol. This could be due to a synergistic interaction between captopril and hydrochlorothiazide.

Angiotensin II in primary hypertension, relationship to plasma renin activity, aldosterone and urinary electrolytes

Plasma concentrations of angiotensin II (AII) were studied in 36 patients with primary (essential) hypertension and 15 normotensive control subjects during basal (1 h supine rest), upright and frusemide-stimulated (80 mg orally) conditions. Plasma renin activity (PRA) and plasma aldosterone (PA) were determined on the same occasions. AII was then correlated statistically to PRA, PA and 24-hour urinary excretions of aldosterone (Aldo-U), sodium and potassium and to the blood pressure (BP) levels. The AII values in the hypertensive patients were not statistically significantly different from those in the normotensive subjects. A close relationship was found between the AII values and the corresponding PRA values in the hypertensive patients (r=0.65--0.76, p less than 0.001 for all). Correlations between AII and PA, and AII and Aldo-U were not consistently significant. No correlation was found between AII and BP or between AII and 24-hour urinary electrolytes. The findings point to an intact function between PRA and AII but a disturbed AII-aldosterone interrelation in primary hypertension.

Neurohumoral profiles in patients with hypertrophic cardiomyopathy: differences to hypertensive left ventricular hypertrophy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) or hypertensive heart disease (HHD) have increased concentrations of various neurohumoral factors. Thus, the aim of the present study was to evaluate the differences in the neurohumoral profiles of HCM and HHD.

METHODS AND RESULTS

Plasma concentrations of epinephrine, norepinephrine, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), angiotensin II and endothelin-1 were measured in 40 patients with HCM, 35 with HHD, and 15 controls. Additionally, the concentrations of these neurohumoral factors in the coronary sinus and aortic root were measured in 12 HCM patients and 10 controls. Plasma concentrations of norepinephrine, ANP and BNP were significantly higher in HCM than HHD and controls. In HCM, there was no significant correlation between the left ventricular mass index and any neurohumoral factor. The plasma BNP concentration significantly correlated with left intraventricular pressure gradient in HCM. There were significant differences in the plasma concentrations of ANP and BNP between HCM with and without left ventricular diastolic dysfunction. Transcardiac production of BNP was significantly higher in patients with obstructive HCM than in those with non-obstructive HCM.

CONCLUSIONS

The significant neurohumoral differences between HCM and HHD were the plasma concentrations of norepinephrine, ANP and BNP. In HCM patients, the plasma BNP concentration may reflect the intraventricular pressure gradient and left ventricular diastolic dysfunction whereas the plasma ANP concentration reflects only the left ventricular diastolic dysfunction.

Renal prostaglandin E2 and the renin-angiotensin system in hypertensive disorders in man

We studied renal vein concentrations of prostaglandin E2 (PGE2) and activity of the renin-angiotensin system in 9 normotensive young men (NT), 17 hypertensive patients with unilateral renal artery stenosis (URS), and 26 patients with essential hypertension (EH) of whom 12 had low renin essential hypertension (LRH). The PGE2 concentration, plasma renin activity (PRA), and angiotensin II (A II) were measured in the inferior vena cava and were compared with the mean concentration for both renal veins under basal conditions and without pharmacological interference. The renal vein PGE2 concentrations were higher in NT (p less than 0.01) and URS (p less than 0.05) than in LRH. However, there were no significant differences in A II concentrations between the groups, nor were there any correlations to PGE2 concentrations. The positive correlation between PRA and PGE2 (r = 0.29, p less than 0.02) indicates that PGE2 may contribute to the activation of the renin-angiotensin system or that there may be a common mechanism for stimulation of both hormonal systems. Our results are not compatible with the hypothesis that a reduction of PGE2 production is a specific feature of patients with EH.

Converting enzyme activity and essential hypertension

Serum ACE-activity was studied in 27 young patients with uncomplicated essential hypertension. The possible importance of an increase in ACE for the pathogenesis of essential hypertension was evaluated by comparing the ACE levels to PRA, the plasma concentrations of angiotensin II and to the blood pressure lowering effect of captopril. Mean ACE-activity was slightly but significantly elevated in the hypertensive patients when compared to 28 normotensive control subjects. ACE-activity was not correlated to PRA, angiotensin II or the decrease in blood pressure following captopril. It is concluded that the increase in ACE-activity in essential hypertension is not of pathophysiological or clinical significance.

Captopril and atenolol combined with hydrochlorothiazide in essential hypertension

1 Fifty-seven patients with mild or moderate essential hypertension, mean age 50 (range 31-69) were randomised to treatment with either captopril or atenolol. Twenty-six patients in each group completed the study. 2 Captopril (25-50 mg three times daily) and atenolol (50-100 mg once daily) caused a highly significant fall in blood pressure both supine and standing. 3 When hydrochlorothiazide (25-50 mg once daily) was added a further fall in blood pressure was observed in both groups. 4 Captopril as single drug caused no significant change in heart rate, while atenolol significantly reduced heart rate both supine and standing. 5 Two patients were excluded from the captopril group, one because of a reversible loss of taste and the other because of dizziness. Three patients were excluded from the atenolol group, two because of bradyarrhythmias and one because of inadequate blood pressure response. 6 Both captopril and atenolol were found to be effective antihypertensive agents, suitable for the treatment of essential hypertension.

Responsiveness of the renin-aldosterone system during exercise in young patients with essential hypertension

The effect of exercise of gradually increased intensity, i.e. 75 W for 20 min followed by 100 W for 20 min, on plasma renin concentration (PRC) and plasma aldosterone concentration (PAC) was studied in young patients with essential hypertension and normotensive control subjects. During exercise without previous sodium loading PRC and PAC increased to the same degree in both hypertensives and normotensives during light exercise; PRC increased further significantly in the normotensives (63 to 72 microIU/ml (medians), P less than 0.01) but not in the hypertensives (46 to 51 microIU/ml) during heavy exercise. PRC and PAC were significantly correlated during both 75 W (rho = 0.633, P less than 0.05) and 100 W (rho = 0.635, P less than 0.05) exercise in the normotensives, but not in the hypertensives. During exercise after loading with 500 ml sodium chloride (0.85 mol/l) PRC and PAC increased in both hypertensives (28 to 42 microIU/ml, P less than 0.01; 0.11 to 0.53 nmol/l, P less than 0.01) and normotensives (22 to 33 microIU/ml, P less than 0.02; 0.12 to 0.34 nmol/l, P less than 0.01), although to a considerably lower degree than without previous loading. PRC and PAC were, however, significantly higher in the hypertensive than in the normotensive group after exercise. It is suggested that the responsiveness of the renin-aldosterone system is abnormal during exercise in young patients with mild essential hypertension, both without and with previous intravenous sodium loading.

Effect of aminoglutethimide on blood pressure and steroid secretion in patients with low renin essential hypertension

An inhibitor of adrenal steroid biosynthesis, aminoglutethimide, was administered to seven patients with low renin essential hypertension, and the antihypertensive action of the drug was compared with its effects on adrenal steroid production. In all patients aldosterone concentrations in plasma and urine were within normal limits before the study. Mean arterial pressure was reduced from a pretreatment value of 117+/-2 (mean+/-SE) mm Hg to 108+/-3 mm Hg after 4 days of aminoglutethimide therapy and further to 99+/-3 mm Hg when drug administration was stopped (usually 21 days). Body weight was also reduced from 81.6+/-7.2 kg in the control period to 80.6+/-7.0 kg after 4 days of drug treatment and to 80.1+/-6.7 kg at the termination of therapy. Plasma renin activity was not significantly increased after 4 days of treatment but had risen to the normal range by the termination of aminoglutethimide therapy. Mean plasma concentrations of deoxycorticosterone and cortisol were unchanged during aminoglutethimide treatment whereas those of 18-hydroxydeoxycorticosterone, progesterone, 17alpha-hydroxyprogesterone, and 11-deoxycortisol were increased as compared to pretreatment values. In contrast, aminoglutethimide treatment reduced mean plasma aldosterone concentrations to about 30% of control values. Excretion rates of 16beta-hydroxydehydroepiandrosterone, 16-oxo-androstenediol, 17-hydroxycorticosteroids and 17-ketosteroids, and the secretion rate of 16beta-hydroxydehydroepiandrosterone were not significantly altered by aminoglutethimide treatment whereas the excretion rate of aldosterone was reduced from 3.62+/-0.5 (mean+/-SE) in the control period to 0.9+/-0.2 mug/24 h after 4 days and to 1.1+/-0.3 mug/24 h at the termination of aminoglutethimide treatment. The gradual lowering of blood pressure and body weight during aminoglutethimide therapy is consistent with the view that the antihypertensive effect of the drug is mediated through a reduction in the patients' extracellular fluid volume, probably secondary to the persistent decrease in aldosterone production. The observation that chronic administration of aminoglutethimide lowered blood pressure in these patients and elevated their plasma renin activity to the normal range without decreasing production of the adrenal steroids, deoxycorticosterone, 18-hydroxydeoxycorticosterone, and 16beta-hydroxydehydroepiandrosterone, makes it unlikely that these steroids are responsible either for the decreased renin or the elevated blood pressure in patients with low renin essential hypertension.