Mechanism by which albumin stimulates renin secretion in isolated kidneys and juxtaglomerular cells.

1. Raising albumin concentration stimulates renin secretion in isolated perfused kidneys and isolated juxtaglomerular cells. 2. In isolated perfused kidneys, raising albumin concentration from 20 to 120 g/l. increased renin secretion and perfusate flow when the perfusion medium contained 1.82 mM-total or ionized Ca. Removing the renal capsule abolished the increased flow but not renin secretion. 3. In isolated juxtaglomerular cells, raising albumin concentration from 0 to 60 g/l. increased renin secretion threefold. This was enhanced slightly by removing Ca. Raising Ca, removing or raising K to 50 mM, or lowering Na to 25 mM inhibited renin secretion. 4. Raising pH from 7.36 to 7.64 inhibited renin secretion whether albumin was present or not. Keeping both pH and ionized Ca constant abolished the stimulatory effect of raising albumin. 5. We conclude that raising albumin concentration in plasma may stimulate renin secretion by several mechanisms, two of which are by lowering ionized Ca and lowering pH, and that both effects may be on the juxtaglomerular cells directly. We also conclude that raising pH per se has a powerful inhibitory effect on renin secretion.