Plasma 18-hydroxycorticosterone during continuous ambulatory peritoneal dialysis.

Continuous ambulatory peritoneal dialysis (CAPD) entails the continuous presence of hypertonic dialysate in the peritoneal cavity. We postulated that the continuous, gradual ultrafiltration produces chronic activation of the renin-angiotensin system and the adrenal zona glomerulosa. To explore this hypothesis, we measured plasma levels of PRA, active renin (AR), total renin (TR), inactive renin (IR), 18-hydroxycorticosterone (18-OH-B), and aldosterone (PAC) under basal and stimulated conditions. At 0800 and 1200 hr after overnight recumbency, plasma levels of PRA, AR, TR, IR, and 18-OH-B were elevated above the range for sodium-replete recumbent normal subjects. PAC, however, was normal. The increase in TR was due predominantly to an increase in AR. After the combined stimulus of 4 hr ambulation and the ultrafiltration induced by a 2 L exchange, plasma levels of PRA, AR, TR, IR, and PAC were within the range for sodium-replete upright normal subjects. Plasma 18-OH-B levels, however, remained markedly elevated. Graded intravenous infusion of ACTH at rates of 0.03 to 10 ng/min demonstrated that the threshold for an ACTH-stimulated rise in plasma 18-OH-B and PAC is at least as low as that for cortisol and corticosterone. We conclude that CAPD produces activation of the renin-angiotensin system. The high circulating levels of PRA, AR, and, presumably, angiotensin II result in increased secretion of 18-OH-B by the adrenal zona glomerulosa.