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

Previously, we showed that estradiol replacement in ovariectomized rats pro duced prominent increases in serum and liver alpha-tocopherol (alpha TP). T he present study was conducted to examine whether the estrogen-induced incr ease in the liver concentrations of alpha TP affects its biliary secretion and the fatty acid compositions of hepatic and biliary lipids. Ten ovariect omized rats were assigned to two groups: five rats were implanted subcutane ously with time-release estradiol pellets (OXE; 25 mu g/day/rat) anf five w ith placebo (OXP). Twice daily rats were pair-fed a modified AIN-93G diet c ontaining soybean oil. At 5 weeks, bile was collected via a bile cannula ho urly for 8 hours during duodenal infusion of a lipid emulsion (565 mu mol t riolein and 396 mu mol Na-taurocholate/24 mt phosphate buffered saline, pH 6.45) at 3.0 mL/hr. During the 8-hour period, no difference was noted in th e hourly rate of bile flow (0.95 mL/hr ill OXE rats va. 0.99 mL/hr in OXP r ats). The biliary output of alpha TP for 8 hours was higher in OXE rats (51 .6 +/- 3.6 nmol) than OXP rats (31.7 +/-. 2.9 nmol). Likewise, the liver co ncentration of alpha TP was higher ill OXE rats (81.9 +/- 3.5 nmol/g liver) than in OXP rats (53.3 +/- 7.4 nmol/g liver). The biliary secretion of pho spholipids (PL) for 8 hours was significantly (P < 0.05) higher in OXE mts (55.1 +/- 4.9 mu mol) than in OXP rats (42.3 +/- 4.7 mu mol). Among the PL fatty acids, the outputs of 20:4 and 22:6n-3 were increased most Markedly b y estradiol replacement. The total outputs of 22:6n-3 for 8 hours in OXE an d OXP rats were 2.95 +/- 0.20 mu mol and 1.37 +/- 0.23 mu mol, 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 mall protect hepatic PL and membranes against oxidative damage by involving the liver status of alpha TP. (C) Elsevier Science Inc. 1999. All rights reserv ed.