Effects of salicylate and two benzoates on contractions of the field-stimulated guinea-pig vas deferens and atrium.

Na salicylate (3.75-30 mmol/l), Na benzoate (10.5-84 mmol/l) and Na metaiodobenzoate (0.375-0.8 mmol/l) concentration dependently reduced the contractile force of the field-stimulated guinea-pig vas deferens. Contractions elicited by either noradrenaline (0.5 mmol/l) or direct muscle stimulation were also reduced while the maximum twitch response induced by KCl (160 mmol/l) was unaffected. The twitch-inhibiting potency of salicylate and the benzoates correlated to their lipophilicity. The positive inotropic effect of field stimulation of the atrium during the refractory period was not altered by the two benzoates but was reduced by Na salicylate. It is concluded that salicylate and benzoate anions are incorporated into smooth muscle cell membranes of the vas and reduce excitability. No binding seems to occur in membranes of the atrial myocardium or the sympathetic neuron terminals and salicylate or benzoate compounds do not interfere with the liberation of neurotransmitters. In addition to its influence on the cell membrane Na salicylate can diminish contractions by uncoupling oxidative phosphorylation. The use of benzoates can help to distinguish between the two effects.