Secretory effects of 6-hydroxydopamine in normal and denervated submaxillary glands of the rat.

Injection of 6-hydroxydopamine (6-OH-DA) elicited a marked and sustained secretory response of control and surgically sympathectomized submaxillary glands of rats. These responses were diminished by previous treatment with reserpine 0.1 mg/kg 48 and 24 h before the experiment and almost abolished by 5 mg/kg reserpine 6 h before the administration of 6-OH-DA. The responses to 6-OH-DA were potentiated in control glands by previous preganglionic denervation of either the parasympathetic or sympathetic nerves of the gland. Development of postjunctional supersensitivity in denervated glands also increased the responses to 6-OH-DA, while atropine had a feeble blocking action. For all these responses, the adrenal catecholamines played no role. After two consecutive doses of 6-OH-DA a third dose of the drug still elicited a secretory response that was 50% of that of the first dose. It is concluded that for the responses to 6-OH-DA the leakage of noradrenaline from the degenerating adrengic nerve endings of the submaxillary gland plays a partial role. Noradrenaline released by the drug from other tissues and reaching the gland via the circulation also contributes to the responses observed. A muscarinic component may also participate in the secretory effects of 6-OH-DA.