The Effects of Angiotensin-Converting Enzyme Inhibition on Sodium Handling in Patients with Advanced Chronic Obstructive Pulmonary Disease

Ten clinically stable, hypercapneic patients with advanced chronic obstructive pulmonary disease were studied to assess the effect of angiotensin-converting enzyme blockade on their inability to excrete a sodium load. Renal, hormonal, and cardiovascular responses to sodium loading were determined during two 5.5-h studies: control day, placebo; and experimental day, captopril. At baseline, compared with control subjects, patients displayed a decrease in urinary sodium associated with low effective renal plasma flow and high plasma level of aldosterone. Captopril, given before sodium loading, produced a significant increase in urinary sodium without increasing effective renal plasma flow and without suppressing plasma aldosterone more than sodium loading alone. Thus, the mechanism by which angiotensin-converting enzyme inhibition induces an acute sodium diuresis in these patients remains to be elucidated. The blockade of angiotensin with captopril also affected the osmotic regulation of vasopressin: for a given increase in plasma osmolality, the increase in plasma vasopressin was subnormal, a finding consistent with the hypothesis that angiotensin II contributes to the regulation of vasopressin secretion.