Negative feedback potency of estradiol is increased in orchidectomized sheep during chronic nutrient restriction

The effect of nutrient restriction on serum concentrations of the gonadotropins, on the pattern of LH secretion, and on sensitivity to estradiol (E2) was assessed in orchidectomized sheep (wethers). Thirty-six wethers (initial weight = 42.3 +/- 0.6 kg) were fed to gain, maintain, or lose body weight (feeding groups G, M, and L, respectively; n = 12 wethers/group). After 7 wk of controlled feeding, G, M, and L wethers weighed 57.0 +/- 1.7, 42.5 +/- 0.6, and 36.6 +/- 0.8 kg, respectively. At the end of controlled feeding, serum concentrations of LH and FSH in M and L wethers were significantly higher than levels in G wethers. During Days 51-54 of controlled feeding, six animals from each feeding group received E2 or vehicle as a continuous infusion. The pattern of LH secretion was assessed 48 h after initiation of infusion. Although E2 infusion did not affect (p > 0.05) LH pulse frequency in G and M wethers, pulse frequency was reduced (p < 0.05) in L wethers receiving E2. These data indicate that serum concentrations of gonadotropins are increased in wethers fed to maintain or lose body weight. In addition, the negative feedback potency of E2 is enhanced during prolonged weight loss.