1047 SECRETION OF ACTIVE AND INACTIVE RENIN BY THE DEVELOPING KIDNEY

Abstract

We have determined the concentration and secretion of active renin (ARC and ARS) and the acid-activated form of inactive renin (IRC and IRS) in anesthetized pigs between the ages of 3 and 57 days. IR was activated by dialysis of plasma at pH 3.3, and angiotensin I was estimated by radioimmunoassay. Both AR and IR were found in plasma of newborn and adult animals. ARC decreased from 4 ± 1 (sem) to 0.6 ± 0.1 ng/ml between 3 and 57 days while IRC declined from 11 ± 3 to 3 ± 1 ng/ml. However, ARS and IRS were unchanged during this time (ARS = 12 ± 5 and 8 ± 4 ng/min and IRS = 31 ± 16 and 55 ± 23 ng/min at 3 and 57 days, respectively). Isoproterenol significantly increased ARS and IRS at all ages. Intravenous furosemide also stimulated secretion of both forms of renin, while propranolol and indomethacin suppressed secretion. ARC as a percentage of the total renin concentration was the same in simultaneously drawn arterial and renal venous plasma. However, AR represented 31 ± 2% of total renin at 3 days and decreased to 20 ± 4% at 57 days. We conclude 1) IR is present in the newborn pig; 2) IRC and ARC decrease with age; 3) changes in IRC and ARC with age may be related to metabolic clearance of renin; 4) control of ARS and IRS are qualitatively similar at different ages. No evidence for systemic activation of IR was found. The change in proportions of AR and IR in plasma may be related to changes in intrarenal storage of renin.

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