PULMONARY CLEARANCE AND RELEASE OF NOREPINEPHRINE AND EPINEPHRINE IN NEWBORN LAMBS

To examine the pulmonary kinetics of the catecholamines norepinephrine and epinephrine immediately after birth, eight fetal lambs were instr umented with vascular catheters under general anesthesia at 133-134 da ys gestation (term = 147 days) and were delivered by cesarean section 1 wk later. Pulmonary norepinephrine and epinephrine kinetics were the n studied 1 and 4 h after birth using radiotracer dilution methodology . The pulmonary fractional extraction of norepinephrine was similar in 1-h (0.111 +/- 0.021) and 4-h (0.117 +/- 0.023) lambs and constituted 24 +/- 5 and 32 +/- 9% of total body norepinephrine clearance, respec tively. Pulmonary removal of epinephrine was less pronounced with a fr actional extraction of 0.035 +/- 0.017 in 1-h and 0.036 +/- 0.013 in 4 -h lambs, which corresponded to 8 +/- 4 and 9 +/- 3% of total body epi nephrine clearance, respectively. Pulmonary spillover of norepinephrin e into the circulation was similar in 1-h (79 +/- 26 ng . min(-1). kg( -1)) and 4-h (82 +/- 18 ng . min(-1) kg(-1)) lambs, and this comprised 27 +/- 8 and 42 +/- 8% of total body norepinephrine spillover, respec tively. Pulmonary epinephrine spillover was not detectable at 1 h, but it occurred in all 4-h lambs, averaging 4.7 +/- 0.8 ng . min(-1) . kg (-)1 or 20 +/- 6% of epinephrine total body spillover. These findings indicate that the lungs of newborn lambs 1) are a major site for remov al of norepinephrine and epinephrine from the circulation; 2) release a substantial quantity of norepinephrine into the circulation, consist ent with the presence of tonic pulmonary sympathetic nerve activity; a nd 3) constitute a significant extra-adrenal source of plasma epinephr ine.