Norepinephrine turnover in lung: effect of cold exposure and chronic hypoxia.

The lung contains sympathetic efferent nerves, but their participation in conditions associated with sympathetic nervous system activation is unknown. To assess sympathetic activity in lung during cold exposure and hypoxia, the measurement of radiolabeled norepinephrine (NE) turnover was carried out in this organ. In preliminary studies this technique, which measures in vivo the activity of sympathetic nerves in an individually innervated organ, was validated for use as a measure of sympathetic activity in rat lung. NE turnover was then measured in unanesthetized rats during cold (4 degrees C, 24 h) and hypobaric hypoxic (PB = 380 Torr, 7 days) exposure. Cold exposure increased calculated NE turnover rate in lung by 63% from 4.2 +/- 1.4 to 6.8 +/- 1.6 ng NE.organ-1.h-1 (95% confidence limits). Chronic hypobaric hypoxia increased NE turnover rate in lung by 114% from 4.0 +/- 1.8 to 8.6 +/- 2.4 NE.organ-1.h-1. Thus NE turnover techniques are applicable to rat lung and demonstrate increased sympathetic activity during cold exposure and chronic hypoxia.