Catecholamine physiology in the ovine fetus. I. Gestational age variation in basal plasma concentrations

Fifty-five ewes with chronically catheterized singleton gestations were studied to assess changes in basal concentrations of fetal catecholamines with increasing gestational age. All pregnancies were time dated, and measurements of catecholamines were conducted at least 5 days after placement of fetal catheters when fetal metabolic parameters had normalized. Plasma concentrations of catecholamines were measured by radioenzymatic assay. Additionally, fetal heart rate (FHR) and corrected mean blood pressure were analyzed in 32 of the fetuses for correlation with plasma levels of catecholamines. Multiple regression analysis revealed significant inverse correlations of fetal plasma concentrations of catecholamines with gestational age, as follows: norepinephrine (p less than 0.001), epinephrine (p less than 0.05), and dopamine (p less than 0.01). FHR correlated inversely with gestational age (p less than 0.001) and positively with circulating levels of norepinephrine (p less than 0.001).