Secretion of Luteinizing Hormone and Follicle Stimulating Hormone in Intact and Ovariectomized Mares in Summer and Winter

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Abstract
Sequential samples of blood were drawn via jugular catheters every 15 min for 24 h from four mares in each of five reproductive states: 1) intact anestrous mares in winter, 2) intact diestrous mares in summer, 3) intact estrous mares in summer, 4) ovariectomized mares in winter and 5) ovariectomized mares in summer. Estrous mares were sampled on d 4 or 5 of estrus and diestrous mares on d 10 or 11 of diestrus. Each sample of plasma was assessed for concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in two independent radioimmuno-assays. A computer program was developed that determined peak hormone concentrations based on 1) assay sensitivity, 2) assay variability and 3) repeatability of peaks in both independent assays. Peaks in LH and FSH were observed for mares in all five reproductive states, except for FSH concentrations in estrous mares. High frequency peaks of short duration were observed only in ovariectomized mares. Low frequency peaks of relatively long duration were observed in both intact and ovariectomized mares in both seasons. With the exception of estrous mares, there was variation among mares in the patterns of LH and(or) FSH within any one group; all estrous mares exhibited high, variable LH concentrations and low, constant FSH concentrations. In general, peaks in both gonadotropins occurred simultaneously. Ovariectomized mares exhibited more (P<.05) peaks/24 h than intact mares for both gonadotropins. Ovariectomized mares also exhibited more (P<.05) FSH peaks/24 h in summer than in winter. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science

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