Aldosterone metabolism in combined isolated perfused rat liver and kidney

The metabolism of aldosterone (Aldo) at 4 nM was studied by radioimmunoassay and by high-performance liquid chromatography in isolated perfused liver (IPL), isolated perfused kidney (IPK), and combined isolated perfused liver and kidney (CIPLK) of male Wistar rats. Effect of D[4-(14)C]aldosterone (D [4-(14)C]Aldo) on the function of IPK of intact and adrenalectomized (ADX) rats was also studied. Aldo clearance in the liver was most important, 16.3 +/- 1.7 ml/min. In IPK, the total clearance of Aldo was 0.27 +/- 0.36 ml/min (39% of the glomerular filtration rate) (GFR). Fractional excretion (FE) of Aldo was 16 +/- 8%. Metabolic clearance of Aldo was (0.21 +/- 0.23 ml/min), 78% of total renal clearance. In CIPLK, the kidney inhibited hepatic clearance of Aldo by 23% when compared with IPL (P less than 0.05). Hepatic Aldo metabolites were predominantly eliminated by biliary excretion of polar metabolites. Several hepatic polar metabolites and tetrahydroaldosterone (THA) accumulated in perfusate and were excreted in the urine in a similar pattern. After hydrolysis of the polar metabolites, some coeluated with THA and dihydroaldosterone (DHA), whereas other metabolites remained more polar than Aldo. Without addition of Aldo, in IPK of ADX rats FENa was higher (P less than 0.01), and FEK was lower (P less than 0.01), resulting in three- to fourfold higher urinary Na-K ratio (P less than 0.01) when compared with IPK and CIPLK of intact rats. In IPK of ADX rats with Aldo in perfusate, only FEK was restored. Addition of Aldo to IPK of intact rats had no effect. However, only in CIPLK, addition of Aldo resulted in an increasing kaliuresis in three subsequent periods of 30 min (0.56-0.95, P less than 0.01). Thus the hepatic metabolites of Aldo could in part mediate the kaliuretic effect of Aldo.