Aldosterone is a mineralocorticoid produced by the zona glomerulosa (ZG) cells of the adrenal cortex. Previous studies have demonstrated that exercise is one of the stresses known to increase aldosterone production. Both potassium and angiotensin II levels in the plasma were correlated with aldosterone secretion during exercise, but the action mechanism is still unclear. In our in vivostudy, male rats were catheterized viaright jugular vein (RJV), and divided into four groups including water immersion, swim, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitrostudy, ZG cells from experimental rats were challenged by lactate (1-10 mM) with or without angiotensin II (10 nM) for 60 min. The levels of plasma angiotensin II and those of aldosterone in plasma and medium were measured by radioimmunoassay. Protein expressions in cell lysates were measured by immunoblotting assay. Ten min after exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. The level of angiotensin II was increased by swimming but not by lactate infusion. The levels of plasma sodium were increased whereas those of plasma potassium were decreased by swimming and infusion of sodium lactate or sodium pyruvate. The responses of plasma osmolality were synchronized with those of plasma sodium in the experimental animals. Administration of angiotensin II (10 nM) in vitrosignificantly increased aldosterone production. Sodium lactate (1-10 mM) alone did not alter the release of aldosterone. Co-incubation of angiotensin II (10 nM) with sodium lactate (10 mM) resulted in an increased production of aldosterone as compared with the group treated with angiotensin II alone. Administration of sodium lactate did not alter the protein expression of P450scc, but enhanced steroidogenic acute regulatory protein (StAR) expression in the presence of angiotensin II (10 nM) in ZG cells. These results demonstrated that short-time exercise led to the increase of aldosterone secretion, which is associated with the increased secretion of angiotensin II and the direct stimulatory effect of lactate on the action of angiotensin II in ZG cells.(poster)