Ovine fetal hormonal and hypothalamic neuroendocrine responses to maternal water deprivation at late gestation

Angiotensin II (Ang II), aldosterone, and arginine-vasopressin (AVP) are three major neuropeptides or hormones that are important in the control of body fluid regulation. Dehydration during pregnancy induces alterations in maternal-fetal fluid homeostasis. It is still not clear about effects and mechanisms of maternal water deprivation on fetal neuroendocine and hormonal responses. The present study deprived water from pregnant sheep at near-term for 24 h and 48 h, and determined maternal and fetal blood osmolality and sodium levels before and immediately after water deprivation. Fetal renal excretion and plasma hormones were measured. Fetal forebrain was analyzed for cellular activation marked with Fos and Fos-B. The results showed that maternal and fetal blood osmolality and sodium were increased by water deprivation. Maternal and fetal Ang II, aldosterone, and AVP levels were elevated by 24-h and 48-h water deprivation, while fetal plasma Ang I levels were increased only under the condition of 48-h water deprivation. Intensive Fos and Fos-B expression was detected in the median preoptic nuclei and paraventricular nuclei in the fetal brain following exposure to maternal water deprivation. Double labeling demonstrated that many Fos-positive cells were AVP-containing neurons in the fetal paraventricular nucleus. Together, the results suggest that neuroendocrine and hormonal regulatory mechanisms play a role in the control of body fluid homeostasis, and relatively matured and functional at the last third of gestation, as well as the fetal hypothalamus is functional in the control of the neuropeptide in response to maternal dehydration.