In vivo and in vitro alterations of active and inactive plasma renins in the rat.

The levels of active, inactive, and total renin (trypsin treatment) were measured in rat plasma before and after in vivo stimulation or suppression of active plasma renin. Stimulation of active renin was accompanied by either an increase (low sodium diet), no change (pentobarbital anesthesia plus hemorrhage), or fall (pentobarbital anesthesia) in the plasma levels of inactive renin, while suppression of active renin was accompanied by a fall (high sodium diet) or mild but nonsignificant increases (clonidine or saline infusion) of the inactive enzyme. These results suggest the possible independence of in vivo regulation of active and inactive renin in the rat. Trypsin activation of plasma fractions obtained by isoeletric focusing indicated a minimum of three activable forms of inactive renin (pH 4.4, 4.6, 4.8). Inactive enzymes could not be completely separated from active renins by this technique. Isoelectric focusing indicated a similar lowering of the isoelectric points of the five detectable active renins of rat plasma following in vivo stimulation of the renin system (ether anesthesia plus hemorrhage) or trypsin treatment of normal rat plasma before fractionation. These results indicate that similar renins are activated both in vivo and in vitro. Although trypsin is not the physiological activator of renin, a similar enzymatic cleavage resulting in activation appears to occur in vivo.