Evidence for an extrarenal source of inactive renin in rats

We studied the source of inactive renin in plasma by investigating the changes of active and inactive renin after bilateral nephrectomy in the rat. Active renin rapidly decreased after bilateral nephrectomy, with a half-life of approximately 15 minutes. Inactive renin, on the other hand, was 20.96 +/- 1.63 ng/ml/hr before nephrectomy and gradually increased to reach a peak at 20 hours after nephrectomy (193 +/- 62 ng/ml/hr). The molecular weight of active renin was approximately 40,000 and that of inactive renin was approximately 60,000 on a Sephacryl S-200 column. Inactive renin was separated from active renin by a Cibacron blue column, and the 0 time inactive renin eluted in the same fractions as the inactive renin from 20 hours after nephrectomy. The pH optimum of inactive renin in rat renin substrate was between 5.5 and 7.5, which differs from the optimal value of pepsin or cathepsin D. The increase of inactive renin in nephrectomized rats was not prevented by removal of the salivary glands, uterus, spleen, pancreas, stomach, intestines, adrenal glands, or pituitary. In summary, inactive renin is present in the anephric rat and does not appear to be converted to active renin in the peripheral blood. The source and control of this extrarenal inactive renin are still unclear, but this renin is secreted in the rat within hours after nephrectomy.