Pulmonary extraction of circulating noradrenaline in man

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Abstract
Pulmonary plasma kinetics of endogenous noradrenaline (NA) and tritium labelled L‐noradrenaline (3H‐NA) was studied in fifteen subjects during pulmonary arterial catheterization. Plasma NA concentration in femoral artery ranged from 0·5 to 8·2 nmol l−1, mean 2·3 nmol l−1, which was not significantly different from that of age‐matched control subjects. The lungs extracted both endogenous NA and 3H‐NA significantly, but no significant pulmonary extraction of endogenous adrenaline was found. The pulmonary arterial‐systemic arterial extraction ratio of NA was mean 0·08 (n= 9) as compared to that of 3H‐NA: mean 0·07 (n= 8, NS). Likewise mean pulmonary clearances of NA and 3H‐NA were not significantly different (97 ml min−1x M−2v. 124 ml min−1x M−2, NS). Estimated whole‐body clearance of noradrenaline was mean 0·80 1 min−1x M−2(n= 6) while the pulmonary clearance amounted to 19% of this value. The small, but significant, pulmonary extraction of circulating noradrenaline implies that whole‐body clearance, as estimated from infusion rate and systemic arterial sampling, will be overestimated by approximately 7%. As pulmonary extraction of NA and 3H‐NA was almost identical, the results indicate no significant pulmonary contribution to circulating noradrenaline.