Hepatic metabolism of 3 alpha-hydroxy-5 beta-etianic acid (3 alpha-hydroxy-5 beta-androstan-17 beta-carboxylic acid) in the adult rat.

摘要

Normal human meconium has been shown to contain short-chain (C20-C22) bile acids and, recently, these compounds have been identified in sera of patients with cholestasis. This suggests that shortchain bile acids may be secreted in bile. We have examined this point by studying the hepatic metabolism and biliary secretion of one naturally occurring C20 bile acid, 3 alpha-hydroxy-5 beta-etianic acid (3 alpha-hydroxy-5 beta-androstan-17 beta-carboxylic acid). [3-3H]-3 alpha-hydroxy-5 beta-etianic acid was prepared and administered intravenously to rats prepared with an external biliary fistula. 85.5 +/- 1.2% of the administered dose was recovered in bile over 20 h with 71.5 +/- 1.3% appearing in the first hour. 11.9 +/- 1.6% of the dose was estimated to be distributed in body water and 0.6 +/- 0.2% was recovered as organic matter in urine. Total recovery of label was 98.0 +/- 2.6%. Administration of milligram quantities of 3 alpha-hydroxy-5 beta-etianic acid produced an increase in bile flow (58.9 +/- 7.1% over basal levels) within 20 min after injection of the steroid. The radiolabeled material in bile was shown by thin-layer chromatography (TLC) to be a polar conjugate which, after beta-glucuronidase hydrolysis, cochromatographed with authentic free 3 alpha-hydroxy-5 beta-etianic acid. After purification, and derivatization, the steroid moiety was proven by gas chromatography-mass spectrometry to be identical to 3 alpha-hydroxy-5 beta-etianic acid. Characterization of the conjugate by TLC and by 3 alpha-hydroxysteroid dehydrogenase assay, before and after beta-glucuronidase hydrolysis, indicated that the steroid was secreted in bile as the 3-O-beta-glucuronide. It is concluded that 3 alpha-hydroxy-5 beta-etianic acid is cleared from the plasma, conjugated with glucuronic acid, and secreted into bile rapidly and in high concentration. The choleretic properties of this shortchain bile acid contrast with the cholestatic effects of lithocholic acid, its C24 analog. Both the form of conjugation of etianic acid and its effect on bile flow suggest that the shortened side chain of this steroid markedly alters its hepatic metabolism and physiology.