EVIDENCE FOR ACTIVATION OF CIRCULATING INACTIVE RENIN BY THE HUMAN-KIDNEY

In 8 patients with essential hypertension (EHT) and 6 patients with renovascular hypertension (RVHT), peripheral venous enzymatically active and inactive renin values were followed after acute stimulation of renin release by the vasodilating agent diazoxide (300 mg i.v.). Active renin rose during the 1st h after diazoxide and remained high during the following 15 h, but inactive renin fell during the 1st h rose thereafter. Peripheral venous active and inactive renin were not different from arterial values both before and after diazoxide. Sixteen patients with EHT received propranolol, 80 mg, 4 times a day. Six had a 1st injection of diazoxide the day before propranolol was started and a 2nd one after 10-14 days of propranolol treatment. Peripheral vein active renin was lowered by propranolol, but inactive renin was raised. Both the diazoxide-induced rapid rise of active renin and the fall of inactive renin observed in untreated patients were absent during treatment with propranolol. In 4 patients with EHT and 7 patients with RVHT, renal vein sampling was performed before and 30 min after diazoxide. Increased release of active renin from kidneys that were not markedly contracted was associated with a fall of the renal vein to peripheral vein ratio of inactive renin to a value less than one. Under certain circumstances stimulated release of active renin is associated with removal of inactive renin from the circulation by the kidney. This may in fact be due to intrarenal transformation of circulating inactive renin into its active counterpart. A .beta.-adrenoreceptor might be involved in this activation process.