Pregnancy zone protein analogue in pregnant and non-pregnant primates, and its decrease during pregnancy in some monkey species.

Rabbit antiserum to human pregnancy zone protein (PZP) cross-reacted with analogous proteins in several species of primates. The chimpanzee PZP showed reactions of identity with human PZP, while the PZP analogue in the orangutan, in four species of old world monkeys (pig-tailed, rhesus, cynomolgus and stump-tailed) and in a species of new world monkey (squirrel) showed equivalent reactions of partial identity with human PZP. In the chimpanzee and orangutan, the PZP analogue was present in low concentrations in non-pregnant animals, but as in the human, it increased quite appreciably during gestation. In the chimpanzee, this increase in pregnancy was about four-fold greater than in the human. In sharp contrast, in the old and new world monkeys, the PZP analogue was present in much higher concentrations in non-pregnant animals than it is in humans. In addition, during pregnancy the PZP analogue in these monkey species actually decreased during pregnancy. In the few cases studied, normal levels were regained about 1 month after delivery. A normal plasma protein, alpha2-macroglobin, was also studied in these primate species, because this protein shares some characteristics with PZP. Analogous alpha2-macroglobulin serum proteins were found in all the primates tested, but the observed gel diffusion identity patterns suggested that this protein was phylogenetically older than PZP. alpha2-macroglobulin increased slightly during human pregnancy, but in all the other primates studied, the alpha-macroglobulin analogue was either unchanged or slightly decreased during gestation.