Renin substrate in plasma under various experimental conditions in the rat

Abstract

Plasma substrate for renin was studied under various experimental conditions in rats. Substrate concentration was determined indirectly by the addition of a high dose of hog renin and indicated as equivalent of angiotensin II (ng) per milliliter of plasma. After bilateral nephrectomy, plasma substrate concentration reaches a maximum within 8 hr. After bilateral adrenalectomy, the plasma substrate is gradually reduced. Low-Na intake also diminishes the plasma substrate concentration, but not as much as adrenalectomy. Overdosage of deoxycorticosterone acetate (DCA) and saline increases plasma substrate, but not more than unilateral nephrectomy. Since endogenous renin production is markedly diminished in DCA-pretreated animals, whereas it is unchanged after unilateral nephrectomy, no correlation could be found between the variations in plasma substrate and endogenous renin. In experimental renal hypertension, plasma substrate is elevated whether or not the plasma renin concentration is increased or unchanged. Low-Na intake reduces the substrate concentration to normal values. Female rats have a lower substrate concentration than males, and plasma substrate is further lowered in pregnancy. The participation of factors other than renin and angiotensinogen in the enzyme-substrate reaction is suggested.