Effects of stimulation of renin release on trypsin-activable renin in rat plasma

Little information is available concerning inactive renin in rat plasma. A renin assay method has now been developed for measurement of active and inactive renin in approximately 0.1 ml rat plasma. Trypsin treatment of plasma (5.0 mg trypsin/ml plasma for 5 min at 0 degrees C) to maximally increase the rate of angiotensin I generation did not alter the Km or pH optimum of the renin reaction. Utilizing trypsin, 79 +/- 6% of the total renin (active + inactive) in normal rat plasma is in the inactive form. In vivo stimulation of renin by restraint stress induces a reciprocal change in active and inactive plasma plasma renin, and exposure of animals to ether elevates active and total renin, whereas inactive renin shows a small but nonstatistical decline. Although a parallel disappearance of active and inactive renin is observed after bilateral nephrectomy of the pentobarbital-anesthetized animal, complete occlusion of the renal arteries and veins after ether-induced renin stimulation results in a significant increase of inactive renin. This suggests that possibility of formation of inactive renin from the active enzyme in high renin states. These studies indicate that the balance of active and trypsin-activable renins in rat plasma may be dependent or not only the method but also the degree of in vivo renin stimulation.