Mineralocorticoid secretion in essential hypertension with normal and low plasma renin activity

Comparison of propranolol or hydrochlorothiazide alone for treatment of hypertension. III. Evaluation of the renin-angiotensin system

In this study, the relation between renin activity and therapeutic response to hydrochlorothiazide or propranolol was studied. Patients with a diastolic blood pressure of 95 to 114 mm Hg were treated with propranolol (40 to 320 mg twice daily) or hydrochlorothiazide (25 to 100 mg twice daily). The initial renin profiles were: low, 56 percent (n = 300); normal, 33 percent (n = 174); high, 11 percent (n = 60). A greater incidence of low and fewer high renin profiles (p less than 0.001) were observed in blacks. After furosemide administration (40 mg intravenously), 55 percent of patients (n = 291) had a low renin response and 45 percent (n = 240) had a normal renin response. No correlation between renin profile and renin response was observed, although low renin response and low renin profile occurred more frequently in older patients. Hydrochlorothiazide administration resulted in a greater decrement in diastolic blood pressure (p less than 0.05) in the total group. Irrespective of renin activity, both hydrochlorothiazide and propranolol reduced diastolic blood pressure. When renin profile was considered, no significant variation in response to hydrochlorothiazide therapy was observed, and there was a greater reduction in diastolic blood pressure in the patients with a high renin profile receiving propranolol. In comparing therapeutic response, patients with a low renin profile had a better response to hydrochlorothiazide, and propranolol was more effective in patients with a high renin profile. The anticipated effect of therapy on plasma renin activity was observed. Although these results are consistent with a volume-vasoconstrictor analysis of hypertension, the results of therapy could not have been prejudged from renin profile or responsivity. The slight differences observed do not warrant the expense of renin determinations when a simple determination of therapeutic response is sufficient.

Renin subgroups in essential hypertension

A nomogram based on the relationship between plasma renin activity and urinary sodium excretion in normal subjects has been used to classify 956 patients with essential hypertension into low, medium and high renin subgroups. Patients with low renin hypertension (27 percent of all patients) were older (P less than 0.001) than patients with medium or normal renin hypertension. They also contained more women (P less than 0.01) and had higher systolic blood pressures than patients with medium renin hypertension. Creatinine clearance, albumin concentration and hematocrit were lower in low renin patients than in patients with medium renin activity. Serum potassium levels were lower, but urinary potassium excretion was higher in low renin patients. Most of the differences in clinical and biochemical parameters could be explained by the differences in age and male:female ratio between the subgroups. Despite lower renin values, aldosterone excretions were similar between the subgroups. Differences in renin activity and differences in aldosterone-renin ratio could not be explained by differences in age, duration of hypertension and sex ratios. Patients with low renin hypertension showed evidence of increased adrenal sensitivity to angiotensin II-induced aldosterone secretion. Patients with high renin hypertension (11 percent of all patients) were younger than patients with medium or normal renin hypertension. Other differences in biochemical characteristics between these renin subgroups included a slightly higher albumin concentration and hematocrit in patients with high renin levels. These differences and the difference in renin activity between patients with high and patients with medium renin essential hypertension could not be explained by differences in age and/or sex ratio between the two subgroups. Despite the higher renin activity, aldosterone excretion was similar between the high and medium renin subgroups. Therefore, patients in the high renin subgroup are characterized by signs of volume contraction and by a relative unresponsiveness of the adrenal gland to angiotensin II-induced aldosterone secretion. The possible role of these differences in the sensitivity of the adrenal gland in sustaining hypertension has yet to be defined.

Radioimmunoassay of free urinary 18-hydroxydeoxycorticosterone (18-OH-DOC) in patients with essential hypertension

Specific antiserum was raised in white New Zealand rabbits using 18-hydroxydeoxycorticosterone-3-oxime-BSA complex as antigen. The urinary free 18-OH-DOC was estimated after dichloromethane extraction and separation in one paper chromatographic system (propylene glycol/toluene). The mean 18-OH-DOC excretion value (+/- S.D.) in normal subjects was 0.861 +/- 0.527 microgram/24 h (n=23). ACTH produced a 25-fold increase in the excretion of free 18-OH-DOC. Dexamethasone suppressed the values to the lower range of sensitivity. 32% of patients of essential hypertension showed a moderate increase in the free urinary 18-OH-DOC values. The mean value (+/- S.D.) in the low renin hypertension group was 2.50 +/- 1.49 microgram/24 h (n=19), in the normal renin patient group 1.84 +/- 1.22 microgram/24 h (n=38). The difference between controls and the hypertensive groups was statistically significant. Among the different hypertensive groups significant differences could not be calculated.

Adrenocortical factors in hypertension. I. Significance of 18-hydroxy-11-deoxycorticosterone

Low renin essential hypertension and the syndrome of mineralocorticoid excess have two features in common, low plasma renin activity and volume-sensitive hypertension. The proposal that both disorders share a common mechanism--because of the ability of agents that inhibit or antagonize the adrenocortical secretion to lower blood pressure in the low renin hypertensive group--appears to be based on a circular argument. The beneficial effect of removal or neutralization of the adrenocortical contribution only constitutes evidence for volume-dependency or sensitivity, which is how the low renin group is defined. Any measure that blocks a component of the normal homeostatic chain for the maintenance of extracellular and intravascular volume including the adrenal cortex would be expected to have a beneficial effect in volume-sensitive hypertension. Evidence for an adrenal factor in low renin hypertension must rest on the isolation of an active substance that reproduces the effect when readministered. 18-Hydroxy-11-deoxycorticosterone (18-OH-DOC) does not meet these criteria. It is not significantly increased in experimental hypertension and, although its overproduction in unselected low renin essential hypertensive patients remains controversial, the magnitude of the reported elevations is insufficient in relation to the low biologic activity of the steroid to account for a significant effect. Apart from its increase in the 17alpha-hydroxylase defect, 18-OH-DOC is increased in primary aldosteronism and may also be an indicator of a histologic variant of the aldosteronoma. On the basis of a large body of evidence showing parallelism between the 11beta- and 18-hydroxylase functions of the fasciculata zone, we have proposed that both enzymic functions are functionally related and may involve the same enzyme protein and catalytic site. According to this view, the secretion of 18-OH-DOC would have no special significance of its own but would be an obligatory consequence of the secretion of fasciculata zone corticosterone.