Administration of sulpiride to anovulatory mares in winter: Effects on prolactin and gonadotropin concentrations, ovarian activity, ovulation and hair shedding

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Sixteen seasonally anovulatory mares were randomly allotted to two groups and injected daily with either sulpiride (1 mg/kg body weight) or vehicle from 14 January to 14 February. Sulpiride administration increased daily plasma prolactin concentrations (P < 0.05), although the prolactin response during the 6 h following sulpiride injections decreased markedly from the 1st to the 6th day of treatment (treatment by day, P < 0.0001). Plasma concentrations of LH and FSH were not affected by treatment (P > 0.1). Injection of GnRH and TRH on 15 February showed that the response of plasma prolactin to secretagogue was increased in sulpiride-treated mares (P < 0.005), while there was no effect (P > 0.1) of sulpiride treatment on the response of LH or FSH. Both treatment groups had similar changes in numbers of follicles 10-19 and ≥20 mm during the experiment (P > 0.1). Similarly, the mean change in maximal follicular size was not affected by treatment (P > 0.9). No mare ovulated during the study, and plasma progesterone concentrations were similar in both groups (P > 0.1), always at levels <1 ng/ml. Hair shedding increased with time in all mares (P < 0.001) and was increased by sulpiride injections (P = 0.09). It was concluded that sulpiride administration to seasonally anovulatory mares under the conditions of our experiment increased daily plasma prolactin levels but did not stimulate gonadotropin secretion or ovarian activity. © 2002 Elsevier Science Inc. All rights reserved.

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