Roles of the basal level of LH and FSH in the regulation of follicular development during pseudopregnancy in the rat

Present study was conducted to investigate roles of the basal level of FSH and LH in the follicular maturation and maintenance during pseudopregnancy of the rat. Antiserum against luteinizing hormone releasing ghormone (LHRH-AS) or charcoal-treated porcine follicular fluid (PFF; a crude inhibin preparation) was given to individual animals on day 5 of pseudopregnancy. Plasma LH and inhibin decreased after treatment with LHRH-AS. Contrarily, plasma FSH increased after LHRH-AS injection. The number of follicles capable of ovulating in response to human chorionic gonadotropin (hCG) in animals given LHRH-AS declined gradually, reached a nedir at 24 h after the treatment, and then returned to control levels during the subsequent 24 h. On the other hand, plasma FSH levels in rats given three injections of 0.5 ml PFF at 6-h intervals, compared to those in control animals, remained significantly lower at nearly all time points during the first 24 h after the initial PFF injection, and thereafter the hormone levels temporarily increased, being significantly elevated above the control value at 30 and 42 h after the initial PFF injection. Only in the rats given intraperitoneal injections of 0.5 ml PFF, compared to the control animals, plasma LH concentrations remained significantly lower at 9 h after the initial PFF injection and those values were significantly higher at 36 h after the initial treatment. The number of follicles capable of ovulating in response to hCG decreased in PFF-treated animals in a dose-dependent-manner. The follicular development in animals given injection of 0.5 ml PFF were virtually or completely inhibited from 12 to 36 h after the initial injection of PFF. Present results clearly indicate that the basal secretion of both LH and FSH are essential for follicular development and maintenance during pseudopregnancy of the rat