THE EFFECT OF PRETREATMENT WITH A GONADOTROPIN-RELEASING-HORMONE AGONIST ON REPRODUCTIVE FUNCTIONS IN MATURE CYCLING RATS

In order to investigate the performance of follicles in a rat model in which gonadotrophin-releasing hormone agonist (GnRHa) was used for hy pothalamic-pituitary-ovarian axis suppression, three groups of mature cycling rats were studied. One group was treated with buserelin follow ed by pregnant mare's serum gonadotrophin (PMSG), and the second group was treated with PMSG alone. Both these hormonally treated groups rec eived human chorionic gonadotrophin for induction of ovulation, The th ird group received no hormonal treatment, The average number of ovulat ed oocytes recovered from rat oviducts pre-treated with GnRHa was sign ificantly higher than that in rats treated with the gonadotrophin alon e, in spite of the larger number of pre-ovulatory follicles present in the gonadotrophin-treated group. The morphology of both the pre-ovula tory and the post-ovulatory cumulus-oocyte complexes in the three grou ps appeared similar. No difference in the capacity of follicles of the three groups to synthesize progesterone in vitro in response to lutei nizing hormone could be observed. We conclude that ovarian morphology and function are not impaired by pre-treatment with buserelin.