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Estradiol Induces and Progesterone Inhibits The Preovulatory Surges of Luteinizing Hormone and Follicle-Stimulating Hormone in Heifers1

1982; Oxford University Press; Volume: 26; Issue: 4 Linguagem: Inglês

10.1095/biolreprod26.4.571

1529-7268

James S. Kesner, Vasantha Padmanabhan, E. Μ. Convey,

Ruminant Nutrition and Digestive Physiology

Objectives were to determine: 1) whether estradiol, given via implants in amounts to stimulate a proestrus increase, induces preovulatory-like luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges; and 2) whether progesterone, given via infusion in amounts to simulate concentrations found in blood during the luteal phase of the estrous cycle, inhibits gonadotropin surges. All heifers were in the luteal phase of an estrous cycle when ovariectomized. Replacement therapy with estradiol and progesterone was started immediately after ovariectomy to mimic luteal phase concentrations of these steroids. Average estradiol (pg/ml) and progesterone (ng/ml) resulting from this replacement were 2.5 and 6.2 respectively; these values were similar (P>0.05) to those on the day before ovariectomy (2.3 and 7.2, respectively). Nevertheless, basal concentrations of LH and FSH increased from 0.7 and 43 ng/ml before ovariectomy to 2.6 and 96 ng/ml, respectively, 24 h after ovariectomy. This may indicate that other ovarian factors are required to maintain low baselines of LH and FSH.