Relaxin Secretion in the Rhesus Monkey1

Serum samples from 55 mature rhesus monkeys were assayed by a porcine relaxin RIA. The results were reported as immunoreactive equivalents of porcine relaxin. No relaxin was detected in serum from five intact male monkeys or from six cycling females sampled every 2 to 3 days during the entire menstrual cycle. Relaxin was detected in sera from pregnant monkeys after the third week of gestation. From this point it was present in serum throughout pregnancy. Relaxin was undetectable in the sera of three ovariectomized pregnant monkeys. These data suggest that the ovary is the major source of circulating relaxin in monkeys. Since relaxin is detectable at a time when the ovary is secreting little progesterone, this suggests little relationship of luteal secretion of these hormones. In women, relaxin is present in serum from the time of the missed menses in pregnancy. There are major differences in luteal function in early pregnancy between monkeys and women with regard to sequential secretion profiles of relaxin and progesterone.