Vas deferens desensitization by noradrenaline and other drugs

Desensitization of the isolated rat vas deferens was demonstrated by using noradrenaline, 5-hydroxytryptamine, carbachol, acetylcholine or barium chloride as a test concentration after a large concentration (concentration producing a contraction that was 80% of the maximum) of the same agonist. The large concentration of noradrenaline caused desensitization in response to 5-hydroxytryptamine and acetylcholine but not to carbachol and barium chloride. Desensitization is not altered by reserpine--in pretreatment of rats with reserpine or reserpine in Tyrode solution--imipramine and 6-hydroxydopamine. Surgical denervation or modification of the sodium and calcium concentration of the Tyrode solution did not either alter desensitization. Results show that in the rat isolated vas deferens desensitization is not mediated by an action of noradrenaline on the adrenergic neuron.