Short- and long-term effects of an LHRH antagonist given during the prepubertal period on follicle dynamics in the rat.

The effects of the suppression of the high gonadotrophin concentrations normally present by the end of the second week of life on ovarian follicle dynamics were studied in immature rats. Gonadotrophins were suppressed by treatment with an LHRH antagonist (LHRH-A; Org. 30276) on days 6, 9, 12 and 15, and the total population of ovarian follicles was studied at 15 and 28 days, on the day of first oestrus and on the day of oestrus at or following 90 and 300 days of age. Primordial follicles were counted and growing follicles were counted and measured. In rats treated with LHRH-A, follicle recruitment into the growing pool was clearly diminished; the number of growing follicles was significantly (P less than 0.01) lower up to the day of first oestrus and the pool of primordial follicles was significantly (P less than 0.05) larger at 15 and 28 days. Ovarian weights were significantly lower in rats treated with LHRH-A until at least 90 days of age. However, on the day of oestrus at or after 90 and 300 days of age, there were no differences in either the pool of primordial follicles or the pool of growing follicles between rats treated with LHRH-A and control rats. There was also no difference between groups in the number of fresh corpora lutea at these ages. It was concluded that the early peak in gonadotrophin concentrations in immature rats causes substantial recruitment of follicles into the growing pool.(ABSTRACT TRUNCATED AT 250 WORDS)