An unusually important role of O-methylation in the disposition of noradrenaline and adrenaline by the dog renal artery.

Using the oil immersion technique, the role of neuronal uptake, monoamine oxidase and COMT in the inactivation of 2 concentrations (0.23 and 2.3 mumol/l) of noradrenaline and adrenaline was determined by the prolongation of the inactivation time caused by cocaine (12 mumol/l), pargyline (1 mmol/l) and U-0521 (50 mumol/l), respectively. The results obtained allow us to conclude that: 1) as previously shown, for the saphenous vein and mesenteric artery, noradrenaline is inactivated more rapidly than adrenaline; 2) in all tissues and for both concentrations of noradrenaline and adrenaline, neuronal uptake is more important for the inactivation of noradrenaline than for that of adrenaline, while O-methylation is more important for the inactivation of adrenaline than for that of noradrenaline. The only exception is that in the renal artery, O-methylation is very clearly the most important pathway of inactivation for both concentrations of both amines.