Responsiveness of plasma aldosterone: dependency upon basal secretory activity

Relationship between impaired aldosterone response to adrenocorticotropic hormone and prevalence of hemodialysis in type 2 diabetic patients without azotemia

The present prospective observational study was designed to assess the prevalence of hemodialysis in type 2 diabetic patients with an impairment of plasma aldosterone responsiveness to adrenocorticotropic hormone (ACTH). Sixty seven patients (43 men and 24 women) were selected. The inclusion criteria were age < 65 years; presence of normoalbuminemia (serum albumin > 3.6 g/dl); and absence of azotemia (serum creatinine < or = 1.2 mg/dl in males, and < or = 1.0 mg/dl in females). Soluble alpha(1-24)-ACTH was injected intramuscularly in a single dose of 0.25 mg after overnight recumbency. The area under the aldosterone curve (aldosterone AUC) was calculated. The diabetic patients were divided into two groups according to the levels of aldosterone AUC. Patients with an aldosterone AUC in the range of 0-381 were considered poor responders (n = 31) and those with an AUC of 397-1,007 were considered good responders (n = 36). The follow-up was performed during a 144-month period. The end point of the study was the introduction of hemodialysis. A total of 14 patients (12 poor responders and 2 good responders; p < 0.001) were introduced to hemodialysis. The prevalence of hemodialysis in the poor responders (5.74 per 100 patient-years) was significantly higher (p < 0.001, log-rank test) than that in the good responders (0.68 per 100 patient-years). One possible explanation is that an inappropriate level of salt intake relative to the impaired plasma aldosterone control may have contributed to the high prevalence of risks and hemodialysis in the poor responders.

Role of prostaglandins in the aldosterone response to ACTH in sodium depleted human subjects

It is well established that the response of plasma aldosterone to ACTH is enhanced in the sodium depleted state. The mechanisms for this phenomenon are not clear, however, and the present study was undertaken to determine the possible participation of endogenous prostaglandins. ACTH, 250 ug by i.m. administration, was given to 10 human subjects pretreated in four different ways: 1. Control, receiving a 200 mEq per day sodium diet; 2. Sodium depletion (60 mEq/day sodium plus furosemide) plus indomethacin; 3. Sodium depletion plus indomethacin plus captopril; and 4. Sodium depletion plus captopril. Only in the last group, in which the prostaglandin cyclooxygenase inhibitor, indomethacin, was not given during the sodium depletion, did an exaggerated aldosterone response to ACTH occur (an increase of 468% compared with an increase of 182% during control, P less than 0.005). The angiotensin converting enzyme inhibitor, captopril, did not effect this response. Thus, endogenous prostaglandins appear to be of far greater importance than the renin-angiotensin system in mediating the increased aldosterone response to ACTH administration during the sodium depleted state in man.

Aldosterone responsiveness to angiotensin II after sodium restriction in subjects with low renin essential hypertension

Plasma aldosterone (PA) responses to sodium restriction (25 mEq sodium/day for 4 days) and to graded angiotensin II (AII) infusions (2, 4 and 8 ng/kg/min each for 30 min) during a low sodium intake were studied in 14 subjects with low renin essential hypertension (LREH) versus 16 normotensive subjects. The PA response to sodium restriction in relation to changes in plasma renin activity (PRA) was estimated by the ratio of PA increment to PRA increment after sodium restriction (delta PA/delta PRA). In 8 of 14 LREH subjects, whose delta PA/delta PRA ratios were normal, the PA responses to the graded AII doses were similar to those in the normotensive subjects. However, in the remaining 6 LREH subjects whose delta PA/delta PRA ratios were high the PA responses to the graded AII doses were greater. Apparently some LREH subjects, whose delta PA/delta PRA ratios after sodium restriction were high, have an abnormally enhanced aldosterone responsiveness to AII under the condition of low sodium intake.

Catecholamines, renin, aldosterone, and blood volume during chronic minoxidil therapy

Several pressor factors were studied before and during chronic minoxidil therapy (median dose 27.5 mg/day) in 16 patients with hypertension that was refractory to conventional drugs. Following treatment with minoxidil and intensified diuretic therapy, blood pressure was decreased markedly; pulse rate, body weight, plasma volume, plasma aldosterone and epinephrine levels were not significantly altered, while plasma renin activity tended to be increased. Supine and upright plasma norepinephrine concentrations were increased by 140 (P less than 0.005) and 50% (P less than 0.05), respectively, but no significant change in urinary norepinephrine excretion was apparent. The latter parameter may not be a close index of sympathetic activity in patients with severe hypertension treated with minoxidil. While a search for underlying pheochromocytoma is always indicated in refractory hypertension, it appears mandatory to evaluate plasma catecholamines prior to or following discontinuation of treatment with minoxidil, to avoid a wrong diagnosis of pheochromocytoma.