Reduction of plasma renin substrate after parturition; role of renin

Abstract

Plasma renin substrate concentration, renin activity, serum sex hormone binding globulin and total protein concentration were measured sequentially in 10 women after elective caesarean section. Plasma renin substrate concentration decreased from 5406 +/- 000 micrograms AI/l (mean +/- SD) at term to 2369 +/- 726 micrograms AI/l 6 days post partum. Plasma renin activity decreased from 6.2 +/- 3.3 micrograms AI/l/h at term to 4.2 +/- 4.0 micrograms AI/l/h 6 days after delivery. Serum sex hormone binding globulin decreased more slowly than plasma renin substrate concentration. Clearance of plasma renin substrate based on plasma renin activity was calculated. This consumption by renin could explain only 12% of the decrement in plasma renin substrate concentration at the steepest part of the plasma renin substrate disappearance curve. It is concluded that metabolic clearance of plasma renin substrate may be much greater than that calculated from plasma renin activity.