Corticotropin-releasing hormone in chimpanzee and gorilla pregnancies

In humans, the length of gestation and the onset of parturition have been linked to the exponential production of placental CRH and a late gestational decline in maternal plasma CRH-binding protein (CRH-BP). CRH has been shown to have direct effects on the myometrium and on the fetal adrenal, where it stimulates production of the estrogen precursor dihydroepiandrosterone sulfate. In vitro placental CRH production is stimulated by cortisol and inhibited by progesterone. To determine whether this mechanism might operate in other apes, we sampled eight chimpanzees and two gorillas through their pregnancies for CRH, CRH-BP, cortisol, estradiol, progesterone, and alpha-fetoprotein. We show that both chimpanzee and gorilla maternal plasma CRH concentrations rise exponentially as observed in the human. The gorillas exhibited a human-like antepartum fall in CRH-BP, whereas CRH-BP in the chimpanzee remained stable. Pregnancy-associated changes in cortisol, estradiol, progesterone, and alpha-fetoprotein were qualitatively similar to those observed in humans. Maternal plasma cortisol correlated with plasma CRH in both gorillas (r = 0.60; P < 0.05) and chimpanzees (r = 0.36; P < 0.02). Further, there was a strong correlation between plasma estradiol and the log of plasma CRH in the gorilla (r = 0.93; P < 0.0001) and in the chimpanzee (r = 0.72; P < 0.001), which is consistent with the hypothesis that placental CRH determines the placental production of estradiol by stimulating the production of fetal adrenal dehydroepiandrosterone sulfate. Plasma CRH and progesterone were positively correlated providing no in vivo support for progesterone inhibition of CRH release.