PLASMA RENIN ACTIVITY AND ALDOSTERONE CONCENTRATION IN NORMAL SUBJECTS AND PATIENTS WITH SALT‐LOSING TYPE OF CONGENITAL ADRENAL HYPERPLASIA DURING INFANCY

Abstract

SUMMARYPlasma renin activity (PRA) and aldosterone concentration (PAC) were determined in normal infants aged 20 days to 1 year as well as in normal neonates and older children. The responses of PRA and PAC to five intramuscular injections of synthetic ACTH‐Z at 6‐hour intervals while on replacement cortisol therapy were also studied in nine infants with salt‐losing type of congenital adrenal hyperplasia due to 21‐hydroxylase deficiency (CAH) of varying severity, using the data obtained in normal infants as control. The mean PRA and PAC decreased with age from the neonatal period, but in infants aged 20 days to 3 months these variables remained as high as those in newborns. They were also remarkably higher in infants aged 4 to 12 months than in older children. In two cases of CAH (cases 1 and 2) where salt wasting symptoms had been only transiently observed during the neonatal period, PAC was markedly elevated in response to ACTH administration, while in the remaining seven infants with CAH (cases 3–9) with persistent salt wasting symptoms, PAC was not elevated at all or only slightly so. PRA, on the other hand, increased with time during the ACTH stimulation in cases 3–9, while it increased and then decreased in cases 1 and 2. These findings suggest that the salt‐wasting symptoms in CAH may arise where there is a tendency toward renal salt loss due to the overproduction of ACTH‐dependent steroids characteristic of this disease, and cannot be compensated for by sufficient secretion of aldosterone. In cases 3–9, the maximal PAC under the ACTH stimulation was 17–44 ng/dl. These levels are comparable to or even higher than the normal range for control older children aged 2–8 years, but the levels were inappropriately low for the marked elevation of PRA in all of them when compared with the mean level in normal infants. Therefore, these data also seem to explain at least in part the well known clinical fact that the salt wasting symptoms in CAH are severe during infancy, requiring the administration of mineralocorticoids in addition to cortisol. However, beyond infancy only the replacement cortisol therapy is necessary to remit the symptoms.