EFFECTS OF INCREASED CORTISOL CONCENTRATION ON OVINE FETAL LEUCINE KINETICS AND PROTEIN-METABOLISM

Fetal protein accretion decreases as gestation progresses, primarily b ecause protein synthesis decreases. Also, glucocorticoid concentration s increase late in gestation, and restraint of growth is one of the mo st consistently noted effects of glucocorticoids. Therefore, this stud y was done to determine whether fetal protein accretion is decreased b y increased cortisol concentration and whether such an effect might be due to decreased protein synthesis or increased proteolysis. Six days after surgery, fetal leucine and protein metabolism was measured in e ight pregnant ewes (114-119 days of gestation) at normal and elevated cortisol concentrations. Arterial blood leucine concentration, fetal l eucine disposal rate, and exogenous leucine uptake were unaffected by cortisol infusion. Fetal leucine decarboxylation, however, increased b y 19% (P < 0.001). Increased fetal cortisol concentration increased fe tal proteolysis by 11% (P < 0.001) but did not affect the use of leuci ne for protein synthesis. Consequently, fetal protein accretion fell b y 34% (P < 0.002). We conclude that increased fetal plasma cortisol co ncentration increases fetal proteolysis, thereby decreasing the rate o f fetal protein accretion, an effect different from the decreased prot ein synthesis reported in late gestation.