Effects of dichloroglyoxime on isolated guinea-pig smooth muscle and atrium

The effects of dichloroglyoxime (DCG) on isolated rings of aorta, main pulmonary artery, trachea and spontaneously-beating atrium of guines-pig were studied. DCG caused concentration- dependent relaxation of the epinephrine-contracted aortic and pulmonary artery rings and of the tone of tracheal rings. Propranolol caused a slight shift to the right in the concentration-effect curves of DCG on these preparations. Quinacrine, an inhibitor of the release of arachidonic acid and its metabolites, caused a significant shift to the right in the concentration-effect curves of DCG on the three preparations. Low concentrations of DCG increased the beating rate of the atrium, an effect which was blocked by propranolol but not by quinacrine whereas large concentrations decreased the beating rate, an effect which was not significantly affected by propranolol or by quinacrine. DCG also caused a concentration-dependent decrease in the contractility of the atrium and this effect was only slightly affected by propranolol or quinacrine. These observations suggest that the relaxant effect of dichloroglyoxime on the smooth muscle may not be mediated by the stimulation of beta adrenoceptors specifically although a nonspecific interaction with these receptors or with the contractile machinery of the cell cannot be excluded. Data with quinacrine suggest that the effects may be mediated by the release of an inhibitory metabolite of arachidonic acid. The results further suggest that in the atrium the effects of DCG may not be specific and they may be partially mediated by the release of catecholamines from the nerve endings.