Mechanism of changes in hepatic sinusoidal and biliary glutathione efflux with age in rats

Abstract

To delineate the kinetic mechanism(s) of declining sinusoidal reduced glutathione (GSH) efflux with age, we perfused livers of male rats ages approximately 1-1.5, approximately 2-3, and approximately 3.5-6 mo old and measured sinusoidal and biliary GSH and oxidized glutathione (GSSG) effluxes. Our results showed declining GSH transport to be solely due to a falling maximum transport rate (Vmax) and not an increasing Michaelis constant (Km)(Vmax = 24.2 +/- 2.95, 15.8 +/- 1.51, and 8.61 +/- 0.75 nmol. min-1.g-1; Km = 3.0 +/- 0.42, 2.6 +/- 0.31, and 2.6 +/- 0.43 mumol/g for the three age groups, respectively). Because hepatocyte membrane potential was earlier implicated as a driving force for GSH efflux and hepatocytes of female rats were reported to be less polarized than those of males, we likewise studied the kinetics of sinusoidal GSH efflux from livers of female rats of three age groups comparable to our males. Vmax in females tended to be lower than in males. This was more pronounced in the youngest group but was diminished in the older groups. Vmax was again the only parameter declining with age in the female livers, from 19.1 +/- 2.25 to 15.0 +/- 0.95 and 7.83 +/- 0.99 nmol.min-1.g-1, whereas Km remained unchanged at 3.0 +/- 0.45, 3.1 +/- 0.35, and 3.2 +/- 0.72 mumol/g, respectively. Age-dependent changes in GSH efflux were not due to a changing membrane potential. There was no appreciable change in the paracellular permeability with age either.(ABSTRACT TRUNCATED AT 250 WORDS)