Possible existence of prorenin in rabbit renal cortex

The possible existence of prorenin (inactive form of renin) in rabbit renal cortex was studied. Renal cortex was homogenized with 0.25 M sucrose. Following centrifugation at 800 g for 10 min, the supernatant (Fraction H) was centrifuged at 20,000 g for 20 min. The pellet (Fraction G) was separated from soluble fraction (Fraction S). Intravenous injection of non-treated Fraction G caused a little blood pressure elevation in rats. However, the pressor activity of the same amount of Fraction G which was frozen and thawed 5 times previously was more than 10 times as that of non-treated one. The renin activity in preincubated fraction G with Fraction S was 2-fold the summation of the activity of renin in each fraction, when measured using indirect method. Fraction S lost not only the renin activity but also the renin activating activity when heated for 5 min at 100 degrees C. Exposure to pH 3.5 made no influence on renin activity in either Fraction G and S.