Absence of postsynaptic DA2 dopamine receptors in the dog renal vasculature

In experiments designed to look for functional postsynaptic DA2 dopamine receptors in the dog renal vasculature, the vascular effects of two selective DA2 receptor agonists, bromocriptine and quinpirole, were studied in pentobarbital-anesthetized dogs. Intra-arterial (i.a.) injections of bromocriptine reduced renal blood flow before and after blockade of alpha-adrenoceptors. I.a. quinpirole produced dose-related increases in renal blood flow which were not altered by blockade of alpha- or beta-adrenoceptors or DA1 dopamine receptors. Neither of the selective DA2 dopamine receptor antagonists, domperidone or YM 09151-2, altered the renal vascular effects of quinpirole, but these were reduced by combined H1 and H2 histamine receptor blockade. The results of these experiments do not support the existence of postsynaptic DA2 dopamine receptors mediating vasodilation in the canine renal vasculature.