Estradiol replacement in ovariectomized rats increases the hepatic concentration and biliary secretion of α-tocopherol and polyunsaturated fatty acids

Abstract

Previously, we showed that estradiol replacement in ovariectomized rats produced prominent increases in serum and liver α-tocopherol (αTP). The present study was conducted to examine whether the estrogen-induced increase in the liver concentrations of αTP affects its biliary secretion and the fatty acid compositions of hepatic and biliary lipids. Ten ovariectomized rats were assigned to two groups: five rats were implanted subcutaneously with time-release estradiol pellets (OXE; 25 μg/day/rat) and five with placebo (OXP). Twice daily rats were pair-fed a modified AIN-93G diet containing soybean oil. At 5 weeks, bile was collected via a bile cannula hourly for 8 hours during duodenal infusion of a lipid emulsion (565 μmol triolein and 396 μmol Na-taurocholate/24 mL phosphate buffered saline, pH 6.45) at 3.0 mL/hr. During the 8-hour period, no difference was noted in the hourly rate of bile flow (0.95 mL/hr in OXE rats vs. 0.99 mL/hr in OXP rats). The biliary output of αTP for 8 hours was higher in OXE rats (51.6 ± 3.6 nmol) than OXP rats (31.7 ± 2.9 nmol). Likewise, the liver concentration of αTP was higher in OXE rats (81.9 ± 3.5 nmol/g liver) than in OXP rats (53.3 ± 7.4 nmol/g liver). The biliary secretion of phospholipids (PL) for 8 hours was significantly ( P < 0.05) higher in OXE rats (55.1 ± 4.9 μmol) than in OXP rats (42.3 ± 4.7 μmol). Among the PL fatty acids, the outputs of 20:4 and 22:6n-3 were increased most markedly by estradiol replacement. The total outputs of 22:6n-3 for 8 hours in OXE and OXP rats were 2.95 ± 0.20 μmol and 1.37 ± 0.23 μmol, respectively. In the liver, the concentrations of PL 22:5n-3 and 22:6n-3 were elevated significantly in OXE rats. The present results suggest that estradiol may protect hepatic PL and membranes against oxidative damage by improving the liver status of αTP.