[Studies on the antipregnancy effect of LHRH-A in mid gestational rats]

In the present study, the antipregnancy effect of (D-Ala6, Pro9-Ethylamide10) LHRH (LHRH-A) on midgestation rats was observed. The results indicate that LHRH-A could terminate pregnancy of all experimented rats by abortion after subcutaneous administration of 200 micrograms LHRH-A (dissolved in vegetable oil) once a day at days 9 to 11 of their pregnancy. It was also found that the serum progesterone level was significantly lowered after the administration of LHRH-A (P less than 0.05); the concomitant administration of megestrol acetate with LHRH-A could almost completely block the antipregnancy effect of LHRH-A on the midgestation rats; LHRH-A showed a strong direct inhibitory effect on luteal cell progesterone secretion in pseudopregnant and midgestation rats. Hence, it is considered that the probable mechanisms for the antipregnancy effect of LHRH-A may be mainly due to the decrease of serum progesterone level caused by the direct inhibitory effect of LHRH-A on midgestation corpus luteum progesterone production.