title: Pulmonary clearance and release of norepinephrine and epinephrine in newborn lambs.
abstract: To examine the pulmonary kinetics of the catecholamines norepinephrine and epinephrine immediately after birth, eight fetal lambs were instrumented with vascular catheters under general anesthesia at 133-134 days gestation (term = 147 days) and were delivered by cesarean section 1 wk later. Pulmonary norepinephrine and epinephrine kinetics were then 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, respectively. Pulmonary removal of epinephrine was less pronounced with a fractional 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 epinephrine clearance, respectively. Pulmonary spillover of norepinephrine 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, respectively. 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 removal of norepinephrine and epinephrine from the circulation; 2) release a substantial quantity of norepinephrine into the circulation, consistent with the presence of tonic pulmonary sympathetic nerve activity; and 3) constitute a significant extra-adrenal source of plasma epinephrine.
authors.affiliation: Institute of Reproduction and Development, Monash University, Clayton, Victoria, Australia.
authors.forename: J J
authors.initials: JJ
authors.lastname: Smolich
authors.forename: H S
authors.initials: HS
authors.lastname: Cox
authors.forename: G
authors.initials: G
authors.lastname: Eisenhofer
authors.forename: M D
authors.initials: MD
authors.lastname: Esler
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001011:Aorta; D001775:Blood Circulation / Q000502:physiology; D002585:Cesarean Section; D004837:Epinephrine / Q000097:blood / Q000378:metabolism*; D005260:Female; D005865:Gestational Age; D008168:Lung / Q000294:innervation / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D008955:Models, Cardiovascular; D009638:Norepinephrine / Q000097:blood / Q000378:metabolism*; D011247:Pregnancy; D011651:Pulmonary Artery; D011652:Pulmonary Circulation / Q000502:physiology*; D011865:Radioisotope Dilution Technique; D012756:Sheep; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors; D014316:Tritium
chemical_list: D014316:Tritium; D009638:Norepinephrine; D004837:Epinephrine