Reversal of diuretic-induced secondary hyperaldosteronism and hypokalemia by enalapril (MK-421): a new angiotensin-converting enzyme inhibitor.

The study reported here prospectively evaluated the prevention of diuretic-induced secondary hyperaldosteronism and hypokalemia by a converting enzyme inhibitor, enalapril (MK 421). Eighteen normal subjects were randomized into three groups: (1) a HCTZ group (hydrochlorothiazide (HCTZ) 50 mg/day); (2) a MK-421 group (MK-421 10 mg/day); and (3) a HCTZ + MK-421 group [HCTZ 50 mg/day plus MK-421 10 mg/day]. Following a five-day control and a 28-day treatment period, the HCTZ group demonstrated an attenuated but persistent secondary hyperaldosteronism and hypokalemia, the MK-421 group manifested a gradual decline in aldosterone secretion, and the HCTZ + MK-421 group had a delayed but effective correction of secondary hyperaldosteronism and hypokalemia at 28 days but not before. In conclusion, MK-421 reversed diuretic-induced secondary hyperaldosteronism and hypokalemia after 28 days of hydrochlorothiazide therapy. Therefore, converting enzyme inhibitors, such as enalapril, provide useful adjunctive therapy in diuretic-treated patients, but potassium supplementation may be required before the start of four weeks of combined therapy.

Temporal enhancement of renin-aldosterone blockade by enalapril, an angiotensin-converting enzyme inhibitor.

Interruption of the renin-aldosterone system with angiotensin-converting enzyme inhibitors (CEI) should result in a low aldosterone secretion, but most investigators have measured aldosterone production only indirectly by plasma aldosterone (PA) levels or urinary metabolites. We evaluated the effects of CEI of the aldosterone secretion rate (ASR) and compared them with PA, urinary tetrahydroaldosterone (THA), plasma renin activity (PRA), and electrolyte balance in six normotensive subjects in a metabolic unit during a control period (5 days) and during administration of 10 mg/day enalapril for 28 days. Our results demonstrated that (1) the ASR did not decline until after 1 wk of CEI therapy and this was reflected by a corresponding decline in the urine potassium:sodium ratio, (2) upright PA levels at day 1 declined, but supine PA levels were unchanged, (3) THA excretion remained essentially unchanged and the THA:ASR ratio rose progressively during therapy, (4) PRA rose and was maximal on day 3, but subsequently declined. In conclusion, enalapril-induced hypoaldosteronism required several days to become demonstrable and this was not accurately assessed by PA or THA--possibly due, in part, to altered aldosterone metabolism. The simultaneous decline in both PRA and ASR could be due to a decrease in renin substrate. Caution is therefore warranted when assessing aldosterone secretion indirectly by either PA levels or urinary metabolites during CEI therapy.

The effect of amiloride on the renin-aldosterone system in primary hyperaldosteronism and Bartter's syndrome.

Amiloride is a potassium-sparing diuretic which has been advocated for the treatment of hypokalemic disorders. This agent was prospectively evaluated in hypokalemic patients with either primary hyperaldosteronism (ten patients) or Bartter's syndrome (five patients). Vital signs, electrolytes, and ambulatory hormonal studies were assessed during a control period and treatment period with amiloride therapy at 10 to 40 mg/day over two to 24 weeks. During the treatment period the systolic and diastolic blood pressure fell significantly in primary hyperaldosteronism but remained unchanged in Bartter's syndrome. In summary, amiloride therapy (1) increased plasma potassium in both diseases; (2) increased plasma renin activity (PRA) in primary hyperaldosteronism but decreased PRA in Bartter's syndrome; and (3) increased plasma aldosterone in both diseases. Since potassium is known to suppress renin production and stimulate aldosterone secretion, correction of the hypokalemia in this study probably accounts for the decreased PRA and increased plasma aldosterone observed in Bartter's syndrome. The increase in both PRA and plasma aldosterone in primary hyperaldosteronism, however, may be evidence of either a direct activation of the renin-aldosterone system or, alternatively, may be due to the mild natriuretic effects of amiloride.

Amiloride in Bartter's syndrome.

Hypokalemia in Bartter's syndrome (BS) is often difficult to correct despite all measures. Amiloride is a new potassium-sparing diuretic that blocks sodium channels in distal renal tubular cells, independent of aldosterone. Four patients with BS were studied, in an outpatient clinic, while on amiloride therapy (10 to 40 mg/day). Before receiving amiloride the patients were treated with combinations of prostaglandin synthetase inhibitors, potassium-sparing diuretics, and potassium supplements. After a baseline observation period, the potassium-sparing diuretics were discontinued and amiloride therapy was instituted. Cumulative mean plasma potassium level rose after amiloride (0.5 mEq/l; P less than 0.05). The mean plasma potassium levels in three of the patients rose and one of these patients eventually became normokalemic. There were very few adverse reactions and none could be attributed to amiloride alone. Amiloride may be a useful and safe drug for the treatment of the hypokalemia of BS.

Amiloride in primary hyperaldosteronism.

Amiloride is a potassium-sparing diuretic used in spontaneous and diuretic-induced hypokalemia. The effect of amiloride was studied prospectively in 12 patients with primary hyperaldosteronism. Four patients had unilateral adrenal adenomas and eight had bilateral adrenal hyperplasia. All patients were hypertensive and their mean plasma potassium levels were low. Amiloride, 10 to 40 mg daily, was given for 6 mo. Mean plasma potassium levels rose (0.96 mEq/l, P less than 0.001) and remained normal throughout the study without potassium supplementation. Mean blood pressure was lowered by amiloride (22/10 mm Hg, P less than 0.001) but normotension required concomitant antihypertensive therapy in most patients. No significant adverse clinical or laboratory experiences could be directly attributed to amiloride therapy. There was no correlation between the response to therapy and the plasma aldosterone levels, aldosterone secretion rate, or presence of a unilateral adrenal adenoma. Our study demonstrates the efficacy of amiloride in the correction of hypokalemia and amelioration of hypertension in primary hyperaldosteronism.