Parturition in nonhuman primates

Abstract

At present the sequence of events at parturition in nonhuman primates is less clear than in some other mammals. In at least the macaque, the best studied of the nonhuman primates, it appears likely that fetal participation in the onset of parturition occurs. Progesterone acts in its classical role of maintaining uterine quiescence; as term approaches its concentration in uterine venous effluent and therefore presumably in the myometrium declines. A prepartum estrogen rise occurs as in sheep, but there is conflicting evidence in macaques whether estrogen administration will either terminate pregnancy or cause a rise in PGF(2α) levels as it does in sheep. There is some evidence that PGF(2α) plays a role in normal parturition in the macaque, and that the declining influence of progesterone is at some point overridden by other events precipitating delivery. The 'other events' are not well defined except by a hazardous extrapolation from other better studied species. More information is needed in the macaque on the interrelationship of progesterone, estrogens, prostaglandins and perhaps on other agents not presently recognized as critical. If the purpose of pregnancy and parturition research among nonhuman primates is to improve understanding of the human counterparts, the macaque, at least as evidenced by the patterns of pregnancy hormones, does not appear to be the best animal. By these limited criteria, either the chimpanzee or marmoset is closer to the human. But mechanism worked out in any animal can be reliably applied to humans only after their direct demonstration in human subjects.