Metabolic and endocrine responses to cold exposure in chronically incubated extrauterine goat fetuses

To investigate developmental aspects of metabolic and endocrine responses to cold exposure in fetuses, we conducted experiments on six goat fetuses, three aged 95-116 d of gestation (dGA; group I), and three aged 122-134 dGA (group II), using an extrauterine fetal incubation system that provided arterio-venous extracorporeal membrane oxygenation (A-V ECMO). The fetuses were cannulated via the umbilical vessels, and their blood gas exchange was totally supported by A-V ECMO, while they were maintained in an isothermal incubator containing artificial amniotic fluid. After confirming that fetuses were in metabolically stable condition in the extrauterine incubation system, fetal core temperature was lowered by 2 degrees C over 2 h by decreasing the temperature of incubating fluid from 39.5 degrees C. During and after cold exposure, fetal heart rate and arterial blood pressure remained unchanged. We observed significant increases in oxygen consumption and plasma concentrations of norepinephrine, epinephrine, adrenocorticotropic hormone, and cortisol in group II but not in group I fetuses. In addition, based on regression analysis, maximal changes of these parameters during cold exposure were linearly correlated with gestational age significantly, and the regression lines were found to intersect the x (gestational age) axis at around 98-106 dGA. These results suggest that metabolic and endocrine responses to cold exposure develop with gestational age in the goat fetus, the responses being manifested around 100 dGA.