Total body catecholamine kinetics before and after birth in spontaneously hypoxemic fetal lambs

To study the effect of fetal hypoxemia on perinatal norepinephrine and epin ephrine total body kinetics, 13 near-term fetal lambs were instrumented wit h vascular catheters under general anesthesia. One week later, norepinephri ne and epinephrine kinetics were measured in normoxemic (n = 7) or spontane ously hypoxemic fetuses (n = 6) with isotope dilution methodology. Hypoxemi c fetuses had lower body (P < 0.02) and placental (P = 0.01) weights and a threefold elevation in plasma norepinephrine (P < 0.005) and epinephrine (P < 0.025) associated with correspondingly higher total body norepinephrine (P < 0.005) and epinephrine (P < 0.05) spillovers. After birth, total body norepinephrine and epinephrine spillover increased 45% and 3.2-fold, respec tively, in normoxemic animals (both P < 0.001). However, in the hypoxemic g roup, norepinephrine total body spillover was unchanged between fetal and l -h lambs and then fell in 4-h lambs (P < 0.005). In addition, total body ep inephrine release rose postnatally (P < 0.05) but less than in the normoxem ic group (P < 0.02). No differences in norepinephrine or epinephrine total body clearance occurred between normoxemic and hypoxemic groups in either f etal or newborn lambs. These findings indicate that in hypoxemic and growth -restricted fetuses 1) elevated circulating norepinephrine and epinephrine levels are related to increased sympathoadrenal activity and 2) birth is as sociated with an initial maintenance and;subsequent decline in global sympa thetic activity but a blunting of adrenal medullary activation.