The action of oestrin on the bitch

The sex cycles in the bitch and in the Primates are both characterized by the occurrence of periodic bleeding from the uterine endometrium. But while in the bitch this bleeding is observed during the time of pro-oestrus, and ovulation and the formation of the corpus luteum occur shortly after its cessation, in the Primates, on the other hand, ovulation and corpus luteum formation take place some time before the menstrual bleeding, the rupture of the follicle occurring about 10-15 days after the beginning of the previous menstrual flow; indeed the luteal activity normally plays an important part in determining those changes in the uterine endometrium characteristic of the premenstrual condition. Moreover, the menstrual bleeding is generally preceded by degeneration of the corpus luteum, though there is good evidence to show that, occasionally, menstruation may occur without any luteal activity whatever. In view of these facts it is generally agreed ( see Corner, 1933) that menstruation in the Primates and the pro-oestrous bleeding in the bitch are not homologous phenomena and it has been suggested that pro-oestrous bleeding is the equivalent of the intermenstrual bleeding which has been described as occurring in the Primates (Hartman, 1930; Papani­colaou, 1933; Hain, 1934). Moreover, recent work on the hormonic basis of these various changes has yielded results which need careful examination. In the first place it seems very likely that the pro-oestrous alterations in the bitch are to a great extent dependent on the activity of the oestrous hormone (Asdell and Marshall, 1927; Meyer and Saiki, 1931). And secondly, the recent work on the action of oestrin in the Primates including the human has emphasized the importance of this hormone in connexion with the causation of menstrual bleeding. For not only may uterine bleeding occur in the complete absence of the luteal secretion (though the majority of observers are agreed that the corpus luteum activity is part of the normal physiological process), but the injection of oestrin into ovariectomized subjects and monkeys is capable of bringing about uterine bleeding, both during the period of administration and after its cessation (Kaufman, 1933; Werner and Collier, 1934; Hisaw, 1935). Thus Werner and Collier (1934) obtained uterine bleeding during the adminis­tration of 400 R. U. daily to ovariectomized patients. Kaufman (1933), treating cases of primary amenorrhoea with hypoplastic genitals, also produced bleeding during the administration of the hormone which was given in doses of some 100,000 M. U. per week; and lastly, Hisaw (1935) reports bleeding induced in castrated Macacus rhesus during the injection of 40 or 80 R. U. per day. It is therefore of special interest to note that Meyer and Saiki (1931) have advanced experimental evidence (including the finding that bleeding occurred only during the period of oestrin injections) suggesting that the reactions of the bitch and of the Primates to the administration of oestrin are essentially different in nature.