Concanavalin A (con A) chromatography of rat plasma revealed the presence of three differently glycosylated forms of renin, including the con A unbound form (renin C), the loosely bound form (renin A), and the tightly bound form (renin B). Rat renal cortical slices in vitro secreted all these forms. They had a different half-life in the plasma after ligation of both renal artery and vein (half-life of 21 +/- 1, 14 +/- 3, and 35 +/- 4 min for renin A, B, and C, respectively). Thus differently glycosylated forms of renin are released from the kidney into the blood circulation and disappear, with a different half-life. Rats were sodium-depleted and captopril-treated (40-60 mg.kg-1.day-1) for 2 wk, and the effects of these treatments on relative proportions of renin A, B, and C were investigated. These treatments elevated plasma renin concentration approximately 60-fold (from 24 +/- 3 to 1,406 +/- 128 ng angiotensin I.h-1.ml-1; P less than 0.01), in association with an increase in the relative percent of renin C in the plasma from 22 +/- 2 to 39 +/- 3% (P less than 0.01). Moreover, the relative proportion of renin C released from the renal cortical slices was significantly higher in the treated than in the control rats (42 +/- 9 vs. 16 +/- 3% of secreted renin, respectively; P less than 0.02). These results show that the predominant release of renin C, with the longest half-life (35 min) in the plasma, contributes to the increased plasma renin concentration in sodium-depleted and captopril-treated rats.