Estradiol increases amounts of messenger ribonucleic acid for gonadotropin-releasing hormone receptors in sheep

Abstract

Two experiments were conducted simultaneously to investigate regulation of amounts of mRNA for GnRH receptors during the periovulatory period in sheep. In the first experiment, amounts of mRNA for GnRH receptors were measured before and after preovulatory surge of LH following regression of the CL by prostaglandin F2 alpha(PGF2 alpha). So that the time of the preovulatory surge of LH could be accurately predicted, ewes received two injections of PGF2 alpha on Day 14 of the estrous cycle. Anterior pituitary glands were collected from 5 control ewes on Day 14 of the estrous cycle (0 h after PGF2 alpha) and at 48, 72, and 96 h after PGF2 alpha (5 ewes per group). The second experiment was conducted to investigate the effects of 17 beta-estradiol on amounts of mRNA for GnRH receptors. On Day 14 of the estrous cycle, 20 ewes were ovariectomized (OVX); 15 of these ewes received estradiol implants when they were OVX (OVXEI). Sixteen hours after OVX, anterior pituitary glands were collected from 5 OVX and 5 OVXEI ewes, and the remaining OVXEI ewes received an i.m. injection of estradiol (25 micrograms in corn oil; OVXEI + E) to induce a preovulatory-like surge of LH. Anterior pituitary glands were collected from OVXEI + E ewes 18 or 54 h after injection of estradiol (n = 5 per group). Half of each anterior pituitary gland was used to measure the number of GnRH receptors. Poly(A)+ RNA was isolated from the remaining half of each anterior pituitary gland, applied to slot blots, and hybridized with a radioactive cDNA probe encoding the ovine GnRH receptor.(ABSTRACT TRUNCATED AT 250 WORDS)