Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

Solutes in Maternal Circulation and Gestational Sac Compartments during Early Human Development

OBJECTIVES

The aim of this study was to review previous work reporting the concentration of solutes measured in maternal circulation, extra-embryonic celomic fluid, and amniotic fluid, to gain insights into the mechanism that could lead to compartmentalization of fluid and solutes within the gestational sac prior to the 12th week of pregnancy.

METHODS

We conducted a Medline and PubMed literature search from January 1990 through March 2004 using the key words amniotic fluid, celomic fluid, coelomic fluid, celocentesis, coelocentesis, amniocentesis, yolk sac and embryonic cavities. We selected those articles describing solutes that had been measured in the same patient in samples obtained prior to 12 weeks' gestation from maternal circulation, celomic fluid and amniotic fluid. Information extracted from these publications included: gestational age at sampling, number of samples evaluated, mean concentration of the solutes in each of the three fluids and bibliographic citation.

RESULTS

We found 73 publications with the key words and selected 13 that met the inclusion criteria. The concentration of 31 solutes reported in each of the three compartments was documented and gradients among compartmental interfaces calculated.

CONCLUSION

This study describes the concentration of solutes measured in maternal circulation, extracelomic fluid and amniotic fluid early in human development. Analysis of calculated gradients across the compartmental interfaces suggests that the shift of fluid may depend on the biophysical properties of the placenta and yolk sac and on graded changes in hydrostatic pressures across compartments.