Prevention of implantation by [D-Trp6-LH-RH in the rat: comparative study with the effects of large doses of HCG on pregnancy.
Effect of large doses of [D-Trp6]-LH-RH and HCG on implantation of fertilized ova was examined in the rat. Subcutaneous administration of 6ug[D-Trp6]-LH-RH per day from days 1 to 5 of pregnancy by an implanted minipump completely prevented the implantation of fertilized ova associated with a dramatic reduction of plasma progesterone on days 4 and 8, with a slight reduction of estradiol on day 4. There was no balooning of the uterus in the exploratory laparatomy on days 8 and 14. Administration of 1000 U of HCG daily from days 1 to 5 partially prevented implantation and completely terminated gestation. However, plasma progesterone and estradiol levels did not differ from those in the control animals. Ovaries in the [D-Trp6]-LH-RH treated rats appeared to be the same in size as those of the control pregnant rats, whereas the ovaries of the HCG-treated rats were hypertrophied. The results suggest that [D-Trp6]-LH-RH prevents nidation through a mechanism different from that for the adverse effect of excess of HCG on pregnancy.
D000818:Animals; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D010064:Embryo Implantation / Q000187:drug effects*; D004958:Estradiol / Q000097:blood; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D051381:Rats
D006063:Chorionic Gonadotropin; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol