Influence of dopamine and dopaminergic agonists on relaxation of isolated rabbit ileum induced by sympathetic nerve stimulation.

The inhibitory effect of noradrenaline, dopamine and four dopaminergic agonists on smooth muscle relaxation induced by nerve stimulation was compared in isolated rabbit ileum. All these compounds inhibit the relaxation evoked by nerve stimulation. Their activity decreased in the following order: bromocriptine, noradrenaline, nomifensine, dopamine, piribedil and apomorphine. Yohimbine inhibited the effect of noradrenaline and to a lesser extent that of dopamine, while the antidopamine agent sulpiride abolished the effect of dopamine, apomorphine and nomifensine. The presynaptic action of these compounds is discussed.