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Keywords:

  • inhibin;
  • pregnancy;
  • marmoset monkeys

Abstract

This study describes the peripheral concentrations of immunoreactive (ir) inhibin, progesterone, and bioactive gonadotrophin during pregnancy in the marmoset monkey, a New World primate. Blood samples were taken every two weeks from six animals from ovulation to parturition. Plasma ir-inhibin concentrations were measured by inhibin α-subunit-directed radioimmunoassay (RIA) and a recently developed two-site immunoradiometric assay (IRMA) which is specific for inhibin αβ dimer. Concentrations of α-inhibin increased (P < 0.001) during early pregnancy to reach a peak on week 12 of pregnancy and showed a positive correlation with bioassayable gonadotrophin concentrations (r = 0.5, n = 64; P < 0.001). The concentrations of both α-inhibin and gonadotrophin showed no further peaks and declined (P < 0.001) to low levels prior to birth. Concentrations of dimeric inhibin were substantially lower than those measured by RIA and did not vary significantly during pregnancy. Progesterone concentrations remained at luteal-phase levels during the first half of pregnancy and increased (P < 0.05) during the second half to reach maximum concentrations just prior to birth. The relationship between α-inhibin, gonadotrophin, and progesterone suggests that the increase in α-inhibin may be luteal in source and under the control of gonadotrophin. The absence of a second increase in α-inhibin later in pregnancy and the finding that lategestation placenta contained very little α-inhibin differs from observations in Old World primates studied and suggests that the placenta may not be a source of inhibin during pregnancy in the marmoset. The finding of high levels of α-inhibin, but not dimeric inhibin, suggests that inhibin-related molecules may have a role other than suppression of pituitary folliclestimulating hormone. © 1994 Wiley-Liss, Inc.