Effect of Single Injections of Estradiol Benzoate on the Normal Human Menstrual Cycle with Special Reference to the Problem of Estrogen Sensitivity

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Abstract
Single injs. of estradiol benzoate early in the cycle caused significant alterations in its normal sequence. Depending on the amt. and upon individual sensitivity, estradiol led to marked shortening; the cycle was lengthened when menstruation was delayed for 16-20 days. In one case intracyclic hemorrhage was produced with 1 mg. estradiol. The alterations were probably due to interference with normal ovarian rhythm. It is suggested that follicular atresia occurred. The greatly shortened and the greatly lengthened cycle were probably almost similar reactions, except that in the former, after a period of ovarian inhibition the estrogen threshold was lowered such that bleeding supervened, whereas in the latter the ovary recovered before the bleeding threshold was reached, and an almost normal cycle followed the inhibited one. By grading the responses to the same and to different amts. of estradiol it was possible to present definite evidence for the existence of estrogen-sensitive and estrogen- resistant types. Estradiol benzoate, used in the manner described, can postpone ovulation. Intracyclic bleeding may be produced by estrogen as well as by progesterone.