Effect of 6-hydroxydopamine incubation on noradrenaline accumulation and on contractile responses in the rat anococcygeus muscle.

The contractile responses of the rat anococcygeus muscle to sympathomimetics, dopaminergic agonists and 5-hydroxytryptamine, but not to acetylcholine, were inhibited by phentolamine (10(-5)M). Following 6-hydroxydopamine incubation (10(-3)M for 3h), the accumulation of noradrenaline was inhibited, contractile responses to noradrenaline were potentiated, responses to tyramine were abolished and responses to acetylcholine were unaltered. Thus, any spasmogen activity due to release of noradrenaline in this muscle was abolished by 6-hydroxydopamine incubation. This method was used to characterise the direct and indirect actions of some sympathomimetics. In addition, dopaminergic agonists and 5-hydroxytryptamine may also act by releasing noradrenaline in this preparation.