The Effect of Hypothyroidism on Menstruation in Adult Rhesus Monkeys *

Edgar Allen was the first investigator to demonstrate that uterine bleeding, or menstruation, could be induced in rhesus monkeys by withdrawal of estrogenic hormone. Hormone withdrawal was accomplished by removal of one or both ovaries, by injury to a large follicle, or by cessation of injections of estrogen in a castrate animal. The previous work of Corner3 had shown that the monkey is a suitable experimental animal for a study of the relation of ovarian function to menstruation. Subsequent investigators have reported the conditions under which endometrial development and subsequent bleeding may be caused. Progesterone, several estrogens, some androgens, corticosteroids, and combinations of these have been shown to influence the structure of the endometrium and the time of bleeding after hormone withdrawal. The anterior hypophysis has only an indirect rOle in menstruation through the regulation of the ovarian cycle and other endocrine organs. Studies have shown that menstruation may occur as a result of the partial or complete withdrawal of estrogen or of progesterone in monkeys and in women. Uterine bleeding in a non-ovulatory cycle cannot be distinguished from an ovulatory cyde, however, without an examination of the ovaries, the endometrium, or both. Other aids are useful in women in diagnosing whether a cycle is ovulatory or anovulatory, but histological examination of the endometrium is the most dependable. In monkeys and women the time of appearance of induced menstruation is influenced by the hormone withdrawn. Thus, removal of an ovary with a secreting corpus luteum, or removal of the corpus luteum only, results in bleeding in about 48 hours. The bleeding after cessation of progesterone injections also occurs about 48 hours after the last injection of progesterone. There is little variation in the time interval. If estrogen alone is given in constant and uniform amounts for 10 to 14 days, menstruation from a proliferative type of endometrium occurs about 8 days after the last injection of estrogen. The time