A COMPARISON OF CERTAIN PROPERTIES OF CATECHOL-O-METHYL TRANSFERASE TO THOSE OF ADRENERGIC BETA RECEPTORS

¹ Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota

A series of catecholamines was studied as substrates for liver catechol-O-methyl transferase (COMT) and as agonists for the adrenergic beta receptor in isolated rabbit atria. The rates of methylation of these amines decreased in the order: (highest) protokylol, isoproterenol, N-methylepinephrine, epinephrine and norepinephrine; their order as beta-receptor agonists was: (most potent) isoproterenol, protokylol, epinephrine, norepinephrine and N-methylepinephrine. Concentrations of beta-receptor blocking agents as high as 1 x 10^-2 M failed to inhibit COMT in vitro. Pyrogallol and U-0521 (3',4'-dihydroxy-2-methyl-propiophenone) were found to be competitive inhibitors of COMT but possessed no beta-receptor blocking activity on the atria. These findings indicate that COMT cannot serve as a model of the beta receptor.