Biliary glutathione secretion in male single comb white leghorn chickens after inhibition of gamma-glutamyl transpeptidase

Abstract

The amount of hepatic export of glutathione into bile and the importance of gamma-glutamyl transpeptidase (gammaGT) activity for catabolizing glutathione in the bile duct, have not been reported previously for domestic fowl. Therefore, the primary objective of this study was to establish baseline values of biliary glutathione, and a secondary objective was to investigate the effect of acivicin (AT-125; a gammaGT inhibitor) on biliary glutathione in the chicken. Cannulae were placed in the carotid artery (to measure blood pressure) and into the left bile duct of anesthetized male Single Comb White Leghorn (SCWL) chickens (n = 5; 17 to 18 wk). The right bile duct was clamped between the liver and gall bladder. Bile samples were collected at 15-min intervals into microcentrifuge tubes (on ice) containing serine borate and iodoacetic acid to prevent glutathione oxidation. After two samples were obtained to establish baseline values, retrograde infusion of AT-125 (30 microLmol/kg BW) was given to inhibit gammaGT activity in the biliary tree. Systemic blood pressure of the birds remained above 100 mm Hg throughout each experiment (90 to 120 min). Bile flow did not change significantly during the experiment and ranged between 0.15+/-0.03 and 0.20+/-0.07 mL/15 min per kg BW. Baseline biliary secretion values of reduced glutathione (GSH), oxidized glutathione (GSSG), and total glutathione (TGSH) were 4.6, 5.9, and 17 nmol/min per kg BW. After AT-125 infusion, biliary GSH levels increased from 15 to 31 nmol/min per kg BW, indicating that considerable gammaGT-mediated catabolism of GSH occurred in the biliary tree of SCWL males. These results indicate that considerable turnover of GSH in the livers of domestic chickens is due to biliary excretion and that substantial recovery of GSH occurs through activity of gammaGT in the biliary tree.