Effects of two venotropic drugs on inactivation and O-methylation of catecholamines in an isolated canine vein.

Clobenoside (1-O-ethyl-3-O-propyl-5,6-di-O-chlorbenzyl-D-glucofuranose, CL) and Venoruton [O-(beta-hydroxyethyl)-rutosides, HR] did not cause supersensitivity to either exogenous or endogenous (stimulation-released) noradrenaline, in strips of the saphenous vein of the dog. Both drugs caused a significant blockade of the inactivation of noradrenaline, in oil immersion experiments. In incubation experiments with 3H-isoprenaline, CL and HR (100 to 900 mumol/l) caused a dose-dependent inhibition of O-methylation; they had additive effects with the COMT inhibitor, U-0521 and their effects were abolished in the presence of hydrocortisone. In incubation experiments with 3H-adrenaline, formation of metanephrine was inhibited, neuronal uptake and oxidative deamination remaining unaffected. After intravenous administration of HR (100 mg/kg), the O-methylating capacity of blood vessels was similarly reduced. It is concluded that CL and HR affected exclusively the extraneuronal O-methylating system (probably both by inhibiting COMT and depressing uptake) and that this effect may contribute to their therapeutic actions.