Different production and decay rates of six renin forms isolated from rat plasma

Rat kidney contains six forms of renin, which are in different proportion from those found in plasma. We tested the hypothesis that differential removal and production of the forms might explain the differences between stored and circulating renins. In one group of rats, the six forms of renin were measured in plasma, 10 min after hemorrhage, or after aortic constriction. Plasma was run on an isoelectric focusing gel, and the six peaks of renin activity were expressed either as angiotensin I per hour per milliliter or as a percentage of the total plasma renin concentration. After hemorrhage or aortic constriction, the concentration of each form was significantly increased; the profile of circulating renin was significantly modified, showing an increase in proportion of form 2 and a decrease of forms 4, 5, and 6. In a second group, the disappearance of each form was measured 0 to 100 min after nephrectomy and fitted a two-exponential decay curve. Interpreted as a two-pool system with degradation from pool 1, the degradation rate decreased progressively, going from form 1 to 6. In a third group, arterial and renal venous blood were collected. The profile of secreted renin was calculated from the arterial venous difference. This profile fitted the prediction of the two-compartment model. Our data support the hypothesis that the proportion of each circulating renin form is the result of a balance between the rate of production of renin of constant composition and the degradation of the six forms at different rates.