The effect of exogenous gondadotropins on the pre-implantation period in the rat

It is well established that the egg implantation in the rat is dependent on a surge of gonadotropin secretion on day 4 of pregnancy. The present experiments were designed in order to demonstrate the possible effect of exogenous administration of gonadotropins during pre-implantation period in pseudopregnant rats, made pregnant after egg transfer. Groups of pseudopregnant rats by sterile mating were injected with different doses of LH and FSH, between 9:00-12:00 A.M. on day 4 of pseudopregnancy; blastocysts were transferred to them in the morning of day 6, instead of day 5. The implantation rate and the number of young born at term were the criteria of the successful extension of the sensitive period of the endometrium by the exogenous gonadotropins. From the results obtained it can be concluded that LH alone acts on the uterine sensitivity by extension of the implantation period.