FETAL SUBSTRATE UPTAKE DURING INCREASED OVINE FETAL CORTISOL CONCENTRATION

Corticosteroid administration adversely affects fetal growth and conse quently, unless metabolic rate increases (thereby increasing the need for fetal metabolic substrates), reduces fetal need for exogenous subs trates. To find whether the uptake of all or only certain metabolic su bstrates was affected by fetal hypercortisolemia, we measured exogenou s uptake of glucose, lactate, and cu-amino nitrogen during fetal hyper cortisolemia in seven late-gestation sheep fetuses. Hydrocortisone inf usion increased fetal cortisol concentrations from normal to values us ually associated with late gestation (4.3 +/- 0.9 vs. 72.5 +/- 5.0 ng/ ml; P < 0.001). In association with increased fetal cortisol concentra tion, both fetal metabolic rate and the uptakes of glucose and lactate remained constant. However, the uptake of alpha-amino nitrogen-contai ning substances fell (39.6 +/- 3.1 vs. 28.5 +/- 3.4 mu mol . kg(-1). m in(-1); P < 0.002) as did the proportion of metabolic rate (0.45 +/- 0 .04 vs. 0.32 +/- 0.04; P < 0.002) that could be supported by metabolis m of these substances. The proportion of fetal metabolic rate that cou ld be supported by complete metabolism of all substrates taken up acro ss the placenta decreased (1.09 +/- 0.07 vs. 0.95 +/- 0.06; P < 0.02). In conclusion, hypercortisolemia alters the composition of oxidative substrates taken up by the sheep fetus and decreases total fetal subst rate uptake. These changes occur within hours of exposure to increased cortisol concentration.