Estradiol feedback effects on the alpha-subunit mRNA in the sheep pituitary gland: correlation with serum and pituitary luteinizing hormone concentrations.

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Abstract
The effects of estradiol feedback on pituitary luteinizing hormone (LH) content, serum LH concentration and in vitro-translated .alpha. subunit was examined in the ewe. Three animal models were used representing positive, negative and no estradiol feedback. Two experiments were carried out: anestrous ewes were treated acutely with 5 Silastic estradiol implants to induce a LH surge (positive feedback), and ovariectomized ewes were treated chronically with an estradiol implant (negative feedback) or were not treated (no feedback). Pituitary RNA was prepared and translated in a cell-free system; the .alpha. subunit was identified by immunoprecipitation and NaDodSO4[sodium dodecyl sulfate]/PAGE [polyacrylamide gel electrophoresis]. RNA (cpm/.mu.g) and immunoprecipitated growth hormone and prolactin were used to evaluate possible differences in RNA translational efficiencies among the treatment groups. In experiment 1, significantly higher amounts of the .alpha. subunit were observed in animals exhibiting an estradiol-induced LH surge than in normal anestrous ewes (P < 0.001). Examination of values from individual animals suggested a correlation between the stage of the LH surge, pituitary LH and translated .alpha. subunit. In experiment 2, the amount of .alpha. subunit observed in animals exposed to chronic estradiol negative feedback was significantly less (P < 0.005) than that in the untreated ovariectomized animals (no feedback) and no different from that in intact anestrous ewes. Both the negative and the positive feedback effects of estradiol may include regulation of the amount of .alpha.-subunit mRNA.

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