Effects of a sustained release formulation of the gonadotrophin-releasing hormone agonist histrelin on serum concentrations of gonadotrophins and oestradiol, and ovarian LH/human chorionic gonadotrophin receptor content in the rat

Pituitary and ovarian function were studied during the loss and recovery of oestrous cyclical activity in rats following treatment with a sustained release formulation of the gonadotrophin-releasing hormone (GnRH) agonist [imidazole benzyl-D-His 6 ,Pro 9 -ethylamide]-GnRH (histrelin). A single s.c. injection of microencapsulated histrelin (10-300 μg peptide/kg) induced a dose-dependent disruption of normal oestrous cyclical activity with a persistent dioestrous-like vaginal cytology