Effects of oestrogen, administered early or late in the oestrous cycle, upon the survival and regression of the corpus luteum of the guinea-pig.

Abstract

In a study of the effects of estrogen administration (usually subcutaneous implantation between the shoulder blades) upon the guinea pig corpus luteum (CL) diethyl stilbestrol estradiol estradiol propionate and estradiol cypionate were administered in various experiments. Estrogen (50 mcg-75 mg) administered before Cycle Day 5 caused premature regression of the CL. After hysterectomy or hemihysterectomy no luteolytic effect occurred in the ovary on the side of the horn which had been removed. The luteolytic effect was greatly reduced by hypophysectomy. $In the animals in which estrogen (10-125 mg) was administered after Day 8 but before Day 15 (50) the estrogen prevented regression of the CL and also brought further growth to sizes even larger than those seen during pregnancy or after hysterectomy. The large CLs contained and secreted a greater amount of progesterone than CLs in a normal cycle. The CLs especially after Day 22 tended to lose their spherical form and became more irregular. The antiluteolytic effect of the dose was expressed even with hypophysectomy at the time of implantation. Since the precocious luteolytic effect caused by administration of estrogen early in the cycle is prevented by hysterectomy or hemihysterectomy the effect must depend on the exogenous hormone stimulating the uterine luteolytic mechanism directly or indirectly. The large dose of estrogen which when administered later in the cycle is able to exert both antiluteolytic and positively luteotrophic effects is much in excess of estimated physiological level. Its actions probably bear no relation to the similar actions of the conceptus.