Central dopamine receptors regulate blood eosinophilia in the rat.

Dopaminergic agents, dopa and apomorphine, affected biphasically the blood eosinophil count in the rat: low doses of the drug elevated, while high doses lowered it. The response to a high dose of dopa was retained in rats pretreated with an inhibitor of dopamine-beta-hydroxylase, U 10, 157, but prevented by a centrally acting dopa decarboxylase inhibitor, NSD 1015. This indicates that the eosinopenia observed after large doses of dopa is due to the action of dopamine formed from the precursor. As intracerebroventricular injections of Ldopa also produce eosinopenia, the central site of dopamine action is indicated. The eosinopenic response to apomorphine was antagonized by a dopamine receptor blocking agent, haloperidol. This indicates that some central dopamine receptors are involved in the regulation of the eosinophil count in circulating blood. The hypophysis seems to play a crucial role in the phenomenon observed, as no eosinopenia was produced by dopa in hypophysectomized rats.