SHEEP MODEL FOR STUDY OF MATERNAL ADRENAL-GLAND FUNCTION DURING PREGNANCY

Our goal was to develop a model for the study of maternal adrenal glan d regulation and the effects of maternal cortisol secretion on fetal h omeostasis, At about 108 days of gestation, before the time of rapid f etal growth or fetal adrenocortical maturation, ewes, under halothane anesthesia with controlled ventilation and positioned in sternal recum bency, were adrenalectomized. Ewes were treated with aldosterone by in travenous infusion (3 mu g/kg of body weight per day) to induce normal late-gestation aldosterone concentration. Ewes were also treated with cortisol; for 2 postoperative days, this infusion (1 to 2 mu g/kg per min) induced plasma concentration similar to that associated with str ess. Thereafter, the dosage of cortisol was reduced to induce plasma v alues similar to normal late-gestation cortisol concentration in ewes (1 mg/kg per day), or to values in nonpregnant ewes (0.6 mg/kg per day ), Administration of cortisol and aldosterone was required to prevent electrolyte imbalance and signs of hypoadrenocorticism. With steroid r eplacement, plasma protein, electrolyte, and glucose concentrations in adrenalectomized ewes were not different from those in sham-operated pregnant ewes, Of 11 adrenalectomized ewes, one died as a result of fa ilure of the infusion pump, and one died as a result of inappropriate treatment for hypoglycemia, Of the remaining ewes, two aborted fetuses , three ewes each delivered one live and one dead fetus, two delivered live singleton fetuses, and two delivered twins, Therefore, this mode l of relative hypoadrenocorticism in pregnancy is feasible and practic al for studying the influence of maternal cortisol concentration on ma ternal and fetal homeostasis.