Functional differences of six forms of renin in rats

Six forms of renin with different isoelectric points (pIs) have been described in rats. This study was designed to determine if any of the renin forms have different biological activities. Each form of rat renin was semipurified and injected intravenously or intraventricularly in Sprague-Dawley rats anesthetized with pentobarbital sodium or Inactin. Changes in blood pressure (BP), renal function, sodium, and water excretion were observed, before and following equipressor doses; the peak response of BP was similar for all forms. However, the half-lives were significantly different. Form 4 (pI = 5.2) caused a significant increase in urine flow, Na, and K excretion, and urinary osmolality when given intravenously. The other forms were without significant effect. Infusion of converting enzyme inhibitor not only completely blocked the BP response, but also prevented the natriuresis and diuresis. This was observed in rats anesthetized with pentobarbital sodium or Inactin. Intraventricular infusions resulted in a diuresis and natriuresis when form 6 (pI = 4.8) was infused, but not with other forms. BP remained unchanged throughout. This study presents evidence that functional differences exist between renin forms.