Ovine fetal metabolism during norepinephrine infusion

Although stress in fetal life not only increases fetal catecholamine concentration but also decreases fetal growth, there have been few studies that define the specific role of catecholamines in mediating the fetal response to stress. None, however, have investigated effects on fetal amino acid or protein metabolism, processes that should be affected during aberrant fetal growth. Therefore, hormone concentrations as well as oxygen, glucose, lactate, and amino nitrogen, leucine, and protein metabolism were measured with and without norepinephrine infusion in fetuses of eight pregnant ewes (118-125 days of gestation). Transumbilical uptake of oxygen increased during norepinephrine infusion, whereas uptake of glucose remained constant and that of lactate and amino acids fell. The proportion of fetal oxidative metabolism that could be supported by transplacental uptake of exogenous substrates was < 1, indicating that endogenous substrates were used to maintain fetal oxidative metabolism and therefore that fetal growth was diminished. Both fetal leucine uptake and oxidation decreased during norepinephrine infusion, as did fetal protein synthesis and proteolysis. Fetal protein synthesis fell more than proteolysis, however. Consequently, fetal protein accretion, a variable closely related to fetal growth, also fell. Thus the effects of norepinephrine infusion in fetuses suggest that fetal catecholamines play an important role not only in altering fetal metabolism but also in regulating fetal growth.