The menstrual cycle of the primates VIII—The œstrin-withdrawal theory of menstruation

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Abstract
VIII. Injections of estrone (keto-hydroxy-estrin) were given to an adult [female] mangabey and an adult [female] common macaque, during the later part of their otherwise normal menstrual cycles. It was assumed, on the basis of external signs of f ollicular activity and other data, that ovulation in these animals, as in the baboon and the rhesus macaque, occurs about the midpoint of the cycle. In the first 7 cycles of the mangabey and in 2 cycles of the macaque, injections were begun after the midpoint of each cycle, and were continued until the onset of uterine bleeding (average daily dose, 500 rat units; av. total amt. injected, 5,700 rat units). The injections did not disturb the normal menstrual rhythm, the av. duration of the exptl. cycles being 31 days, with a range of 28-36 days. Histological study showed that ovulation had occurred in each of these exptl. cycles. In the 8th cycle of the mangabey injections were begun on the 12th day, before the estimated midpoint of the cycle, and were continued until the 50th day of the cycle when the animal fell sick. A total of 33,675 rat units was given. The animal died 4 days later. Uterine bleeding did not occur during this incomplete cycle. Histological examination showed that ovulation had not occurred in this cycle and that the endometrium was in a condition of cystic hyperplasia. The findings do not support the estrin-withdrawal theory of menstruation, which may explain uterine bleeding in non-ovulatory cycles, but which is an inadequate explanation of the bleeding that terminates ovulatory cycles since it does not take into account the action of the secretions of the corpus luteum.[long dash]IX. The sexual skin was denervated in both a rhesus macaque and a pig-tailed macaque by interruption of the lower part of the lumbar sympathetic chains and by bilateral division, in the spinal canal, of all nerves below and including the 6th lumbar. Following these operations, the sexual skin responded to estrone injections in the same way as that of the normal animal. It is concluded that estrone may act directly on the blood vessels of the sexual skin, although the possibility that the nerves of the vessels may exert an influence in the sexual-skin mechanism is not excluded. The course of the pilomotor nerves to the sexual skin had been interrupted in the preparations in which the lumbar sympathetic chains had been divided. Nevertheless the hairs of the sexual skin stood out as they do in the normal active sexual skin during the exptl. phases of estrone activity following these operations. Their erection in the normal animal may be a mechanical result of edema of the subcut. tissue, and not an effect of centrally discharged pilomotor impulses.