On the Regulation of the Primate Corpus Luteum1

A summary is presented of several studies on the regulation of luteal function in primates using the rhesus monkey as an experimental model and involving the role of pituitary hormones the mechanism of the corpus luteum regression and the effect of pregnancy and lactation. Attempts to accurately describe the relationship of the pituitary gland and luteal function during the primate menstrual cycle were made. The time course of circulatory progesterone was determined and a possible relationship between the follicle-stimulating hormone (FSH) and the progesterone cycle is indicated. Although the luteinizing hormone (LH) does not have a primary controlling effect on luteal function low constant levels of LH are necessary for continued luteal function. The role of prolactin in the progesterone cycle appears to be significant but needs further research. Experiments examining the regression of the corpus luteum at the end of the menstrual cycle indicate that estrogen regularly produced during the luteal cycle has a significant inhibitory effect on progesterone secretion and in large amounts can swiftly reduce the duration of menstruation. Estrogen appears to serve as a built-in destroyer of the corpus luteum. Studies of the progress of the corpus luteum in early pregnancy have found that chorionic gonadotropin secreted by the implanting blastocyst maintains the luteum until placental steroid production takes over. Large progesterone-secreting corpora lutea of a surprising size and functional capability have been found in lactating rhesuses. This is apparently the direct consequence of suckling since no hormonal influence was found. The role of prolactin as a possible luteotrophic hormone requires further investigation.