Effect of diet on the clearance of estradiol-17 beta in the ewe

The twinning rate of ewes is poorly related to plasma concentrations of gonadotropins. In this study, we tested an alternative hypothesis for the control of twinning rate, by testing whether nutritional treatment sufficient to affect twinning could alter estrogen metabolism, with a particular focus on the enterohepatic recirculation. Groups of 5 ovariectomized ewes were fed either above maintenance (supplemented) or below maintenance (restricted). The metabolism of estradiol-17 beta was examined by following the fate of a single i.v. injection of 1.45 micrograms [3H]estradiol-17 beta. In both groups, 74% of the radioactivity was recovered from the feces within 10 days, predominantly as free estradiol-17 alpha, but excretion was slower in the nutritionally restricted ewes. A further 6% of injected radioactivity was excreted in the urine, mostly within 24 h, with no effect of dietary group. Radioactivity in plasma was characterized by ion-exchange chromatography and HPLC. Within 30 min of injection, the main circulating radioactive compound was estradiol-17 alpha sulfate. This remained at a greater concentration than free steroid for the next 48 h, and was greater after 16 h (p < 0.05) in plasma of nutritionally restricted ewes than in the supplemented group. At 0.5 and 2 h, the free steroid was almost entirely estradiol-17 beta, but a polar compound, which appeared by 4 h and probably arose by recirculation from the intestine, remained the major unconjugated metabolite in plasma for the next 24 h. Plasma concentrations of this compound were higher (p < 0.05) in the restricted ewes than in the supplemented ewes during this period.(ABSTRACT TRUNCATED AT 250 WORDS)