Aldosterone Metabolism in Cystic Fibrosis (CF)

Abstract

CF patients show inability to retain salt through sweat leading to serious and at times, fatal complications through cardio-vascular collapse. Aldosterone-renin system metabolism has never been accurately determined in this disorder. Five CF patients, 13 to 21 years of age, were studied on an air-conditioned metabolic unit on constant dietary regimens with 9, 109, and 240 mEq/24 h sodium intake for 8-day periods. During each 8-day period of different sodium balance, aldosterone secretion rate (ASR) and plasma renin activity were measured; the latter in both the supine and upright position. All patients were in good sodium metabolic balance and renal electrolyte conservation was normal. On the 109 mEq sodium regimen, the mean ASR was 282 μg/24 h (normal: 91±30.4). In 4 out of 5 patients on the 240 mEq sodium regimen, the mean ASR was 205 μg/24 h (normal: 35.9±16.1); the 5th patient suppressed moderately to ASR 62 μg/24 h. On the 9 mEq sodium regimen, all 5 patients were able to increase normally to ASR 702 μg/24 h (normal mean: 639±441). Plasma renin values were somewhat elevated on the different sodium intakes, but rose normally with the upright posture. Conclusions: In 5 CF patients, ASR and renin values were slightly elevated, but responded normally to decreased oral sodium intake and postural changes. ASR did not suppress as expected on the high sodium intake. This state of slight hyperaldosteronism secondary to increased renin release is probably due to adaptation to frequent excessive sodium losses via the sweat and consequent extracellular volume changes.