Isolated perfused lungs of guinea-pig, in contrast with rat, lack an uptake process for noradrenaline.

The uptake and metabolism of noradrenaline were compared in isolated perfused lungs of guinea-pigs and rats. Lungs were perfused with 3H-(-)-noradrenaline either a) at a concentration of 10 nM for 20 min in experiments to measure the metabolism of the amine or b) at a concentration of 2 nM for 2 min, in the presence or absence of 10 microM cocaine and with MAO and COMT inhibited, in experiments to measure the uptake of noradrenaline. The total formation of metabolites during the 20 min perfusion period was 36.2 +/- 2.3 pmol g-1 (n = 6) in guinea-pig lungs, and 526 +/- 26 pmol g-1 (n = 6) in rat lungs (14.5-fold greater). In guinea-pig lungs, the rate of uptake of noradrenaline was 0.392 +/- 0.044 pmol g-1 min-1 (n = 3) and was unaffected by cocaine, whereas in rat lungs it was 5.63 +/- 0.03 pmol g-1 min-1 (n = 5) and was inhibited (88%) by cocaine. It is concluded from these results that the lungs of the guinea-pig lack the specific uptake process that, in rat lungs, allows removal of noradrenaline from the pulmonary circulation.