Identification and characterization of peripheral neuronal dopamine receptors in the rat

The effects of local administration of the dopamine receptor agonists apomorphine and pergolide were investigated in the isolated autoperfused hindquarters, renal and superior mesenteric vascular beds of the rat, in order to assess whether presynaptic dopamine receptors in these vascular regions could play a role in the hypotensive effect of these agents. In the three vascular beds, local infusion of apomorphine and pergolide did not influence perfusion pressure per se, but clearly reduced the pressure response to electrical stimulation of the sympathetic innervation. Increases in perfusion pressure induced by local administration of noradrenaline were not influenced by apomorphine and pergolide. The inhibitory effect of apomorphine and pergolide on stimulation-evoked pressure responses was completely antagonized by the dopamine receptor antagonist haloperidol. The alpha 2-adrenoceptor antagonist rauwolscine, which completely blocked the inhibitory effect of the alpha 2-adrenoceptor agonist UK-14,304-18 on neurogenic vasoconstriction, had no influence on the inhibitory effect of apomorphine and pergolide. Like haloperidol, the DA2-receptor antagonist domperidone antagonized the inhibition of neurogenic vasoconstriction by apomorphine in the three vascular beds; the DA1-receptor antagonist SCH 23390 had no influence. These results indicate that inhibitory DA2-receptors are present on the sympathetic innervation to the hindquarters, renal and superior mesenteric vascular beds of the rat.