Norepinephrine content and disposition in large and small pulmonary artery of dog.

Comparisons were made between large and small pulmonary arteries in 1) the content of norepinephrine (NE) and 2) the disposition of released NE. Endogenous NE was measured by liquid chromatography with electrochemical detection. The disposition of NE was studied using superfused strips of arteries previously incubated in l-[3H]NE. Superfusate was collected continuously before, during, and after electrical stimulation. 3,4-Dihydroxyphenylglycol (DOPEG) was shown to be of neuronal, and O-methylated metabolites to be of extraneuronal, origin. Thus extraneuronal uptake was estimated directly by measuring the O-methylated metabolites in the superfusate, and neuronal uptake followed by metabolism was estimated by measuring [3H]DOPEG. The magnitude of the neuronal uptake fraction entering vesicles for reuse was estimated from the compensatory increases in [3H]NE and O-methylated metabolites when neuronal uptake was blocked. The predominant route of disposition for NE was neuronal uptake in the small arteries (41% of released NE) but was extraneuronal uptake or NE overflow in the large vessels (35 and 37% of released NE, respectively). Recapture of NE by storage vesicles was greater in small than in large vessels (22 and 7%, respectively, of released NE).