Long-term suppression of reproductive function by a single dose of gonadotropin-releasing hormone antagonists in a sheep model

ObjectiveTo determine the effect of single long-acting doses of GnRH antagonists on reproductive function in a sheep model.DesignObservational, model study.SettingUniversity-affiliated research unit.Animal(s)Nine intact mature Merino sheep in experiment 1 and 12 mature Merino-crossed ewes with the ovary autotransplanted to the neck in experiment 2.Intervention(s)Synchronization of estrous cycle either with intravaginal progestins or prostaglandin F2α analogues and treatment with a single dose of GnRH antagonist; evaluation of reproductive activity, plasma sampling, and ovarian ultrasonography.Main Outcome Measure(s)Determination of estrus behavior; plasma concentrations of P, FSH, LH, and inhibin A; and number and size of ovarian follicles.Result(s)In both experiments, the concentrations of FSH and LH were suppressed when compared with those in control ewes. In experiment 1, the ovulatory cycles were suppressed for ≥55 days in treated sheep. In experiment 2, there were no follicles sized ≥5 mm in treated ewes for 50 days.Conclusion(s)The suppression of the development of large follicles for ≥30 days after a single injection of a long-acting GnRH antagonist provides a novel convenient method of pretreatment before COS.