Effects of insulin infusion on plasma catecholamine concentration in fetal sheep

To evaluate the response of the sympathoadrenal system in fetal sheep receiving exogenous insulin infusion, we measured plasma catecholamine levels in 14 chronically catheterized fetal sheep before and during an infusion of insulin for 2 days. Catecholamine values were measured in fetal arterial plasma by an electrochemical detection method. Fetal plasma norepinephrine and epinephrine concentrations increased significantly during insulin infusion. Significant inverse correlations were observed between the log norepinephrine concentration and fetal arterial oxygen content and glucose values. A significant direct correlation between the log norepinephrine concentration and fetal arterial carbon dioxide concentration was also observed. The log epinephrine concentration correlated inversely with plasma glucose concentration. Increases in fetal heart rate during both the noninfused and insulin-infused states correlated significantly with increases in norepinephrine concentration. We conclude that the sympathoadrenal system is activated during fetal insulin infusion, potentially supporting some of the fetal cardiovascular responses to insulin infusion.