The effect of vasodilator drugs on the noradrenaline constrictor response in the isolated mesenteric artery.

Previous reports have indicated that diazoxide will inhibit the vasoconstrictor response to noradrenaline on isolated aortic strips (Wohl et al. Life Sci. 7, 381 (1968)). Inhibition of the noradrenaline response was dependent on the calcium concentrations. The present study has confirmed this observation in an isolated perfused mesenteric artery preparation. In addition, a calcium-dependent inhibition of the noradrenaline constrictor response was found with theophylline and sodium nitrite but isoproterenol did not inhibit the noradrenaline response. It is suggested that the drugs which inhibit noradrenaline may do so by either blocking calcium receptors or by depleting an intracellular calcium pool necessary for drug-induced vasoconstriction; or by preventing calcium release from such a pool. Blockade of alpha adrenergic receptors is probably not involved since the drugs also blocked the constrictor response to vasopressin. The mechanism of the inhibitory action of these drugs is probably not related to t...