Vascular effects of selective dopamine receptor agonists and antagonists in the rat kidney

The renal vascular effects of dopaminomimetics and dopaminolytics were studied in the isolated perfused rat kidney after pretreatment with phenoxybenzamine (10(-5) M) and sotalol (10(-5) M) and after contraction of the vascular bed with prostaglandin F2 alpha. The DA1- and D1-selective antagonist, SCH 23390, antagonized competitively the relaxation induced by dopamine (pA2 = 9.7 +/- 0.08, m +/- S.D.). On the other hand, (+/-)-DO 710, a D2-preferential benzamide, only antagonized the renal vascular response to dopamine at a concentration 30 times higher than that active on D2 receptors. The ergot derivative, quinpirole, a selective agonist for DA2 and D2 receptors had no renal vascular dopaminomimetic activity, whereas (-)-EOE, a D2-selective ergoline, seemed to be a partial agonist, but 10 times less potent than dopamine. These results confirm the existence of DA1 receptors on the vascular bed of isolated rat kidney but rule out the presence of DA2 receptors. They also reinforce the analogy between DA1 and D1 dopamine receptors.