Relaxin Secretion by the Primate Corpus Luteum During Simulated Early Pregnancy in Hyperstimulated Menstrual Cycles

Peripheral concentrations of immunoreactive relaxin are generally undetectable during the nonfertile menstrual cycle in humans (1, 2) and rhesus monkeys (3, 4), but become measurable during pregnancy (2, 3, 5–7). The major source of relaxin in primates is the corpus luteum (CL)(5, 8–10). Chorionic gonadotropin (CG) induces relaxin secretion in nonpregnant primates (4,11,12) and thus appears to be a primary stimulus for such induction during early pregnancy. Relaxin is thought to play a role in uterine quiescence during pregnancy (13) and may be an important component for successful pregnancy maintenance.