Post-coital contraceptive and uterotrophic effects of luteinizing hormone releasing hormone

LRH, administered subcutaneously (s.c.) or orally (p.o.) to female rats, was capable of interfering with pregnancy when given on various days of gestation. A 100% inhibition of pregnancy was demonstrated at daily s.c. doses of 1000 mug/rat administered over days 1-7; LRH also was effective as an interceptive, terminating pregnancy in 100% of rats when delivered from days 7-12 of pregnancy at a daily dose of 1000 mug/rat s.c. or p.o. An 80% inhibition also was observed in rabbits administered LRH from days 1-7 at a total dose of 1000 mug/kg, s.c. Uterotrophic studies demonstrated that LRH, administered s.c. to intact immature mice, produces a dose-related increase in uterine and ovarian weight and initiates vaginal opening. The hypothalamic hormone also produced a dose-related increase in uterine weight in ovariectomized mice and hypophysectomized rats. The data suggest that LRH has a post-coital contraceptive effect, presumably acting via hyperstimulation of the hypophysial-ovarian steroid-uterine axis, and/or by a direct extrapituitary (uterine) effect.