In VivoRegulation of the Fetal Rhesus Monkey Adrenal Gland*

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Abstract
Fetal adrenal function in utero was studied in chronically catheterized rhesus monkey [M. mulatta] fetuses (129-154 days gestational age). Measurements of fetal pH, p[partial pressure CO2, pO2 [partial pressure O2], heart rate and fetal and maternal blood pressure were normal by 24 h after surgery. Maternal cortisol levels were 484.6 .+-. 60.7 ng/ml (mean .+-. SE) after surgery, decreasing to 300 .+-. 26.9 and 227.8 .+-. 30.6 ng/ml by the 2nd and 3rd day after surgery and stabilizing thereafter. No consistent pattern in fetal cortisol was seen after surgery. A significant increase in fetal concentration was observed between 145 and 149 and 150 and 154 days gestation (87.9 .+-. 9.3 and 123.8 .+-. 20.0 ng/ml, respectively). A significant diurnal variation of cortisol levels was found in the fetal, but not maternal, circulation (fetal levels: AM [ante meridiem], 167 .+-. 13.4 ng/ml, PM [post meridiem], 115 .+-. 8.9 ng/ml; maternal levels: AM, 326 .+-. 18.8 ng/ml; PM, 319 .+-. 38.5 ng/ml). Seven fetuses were challenged with bolus injections of 0.5 IU ACTH. An increase in circulating cortisol levels in response to ACTH was seen in only 2 of the fetuses. Dexamethasone (8 mg/day) was administered in 4 pregnancies. Fetal ACTH decreased from a baseline of 55.8 .+-. 14.5 to 30.5 .+-. 4.1 and 17.9 .+-. 4.5 pg/ml 24 and 48 h after starting the dexamethasone infusion. Basal cortisol levels were 78.5 .+-. 8.7 ng/ml and decreased to 16.4 .+-. 2.8 and 12.3 .+-. 1.6 ng/ml at 24 and 48 h, respectively, after dexamethasone. Both ACTH and cortisol values returned to pretreatment levels after cessation of treatment. These data are interpreted as indicating that fetal adrenal function is regulated by the fetal pituitary. However, the limited response of the fetal adrenal in situ to exogenous ACTH suggests a decreased responsiveness of the gland in utero.

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