Effects of increased cortisol concentration on ovine fetal leucine kinetics and protein metabolism.

Fetal protein accretion decreases as gestation progresses, primarily because protein synthesis decreases. Also, glucocorticoid primarily because protein synthesis decreases. Also, glucocorticoid concentrations increase late in gestation, and restraint of growth is one of the most consistently noted effects of glucocorticoids. Therefore, this study was done to determine whether fetal protein accretion is decreased by 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 eight pregnant ewes (114-119 days of gestation) at normal and elevated cortisol concentrations. Arterial blood leucine concentration, fetal leucine disposal rate, and exogenous leucine uptake were unaffected by cortisol infusion. Fetal leucine decarboxylation, however, increased by 19% (P < 0.001). Increased fetal cortisol concentration increased fetal proteolysis by 11% (P < 0.001) but did not affect the use of leucine for protein synthesis. Consequently, fetal protein accretion fell by 34% (P < 0.002). We conclude that increased fetal plasma cortisol concentration increases fetal proteolysis, thereby decreasing the rate of fetal protein accretion, an effect different from the decreased protein synthesis reported in late gestation.