The α₁-adrenergic receptor not the DA₁-dopaminergic receptor mediates cyclosporine–SKF38393 renovascular interaction

In this study, we investigated the effect of acute exposure to cyclosporine A (CyA) on renal vasodilations evoked by the DA(1) doparnmergic agonist SKF38393 and whether doparnine DA(1) receptors are directly involved in the interaction. Changes evoked by CyA in SKF38393 vasodilations were evaluated in phenylephrine-preconstricted isolated per- fused rat kidneys in the absence and presence of SCH23390, a DA(1) receptor antagonist. SKF38393 (3 x 10(-8) to 3 x 10(-6) mol) produced dose-dependent reductions in the renal perfusion pressure that were significantly attenuated in tissues pretreated with SCH23390 or CyA. Unlike SKF38393, the vasodilatory action of sodium nitroprusside, a nitrovasodilator, was not altered by CyA. The attenuating effect of CyA on SKF38393 vasodilations was preserved in preparations pretreated with SCH23390, suggesting that sites other than DA(1) receptors may be involved in CyA-SKF38393 interaction. The study was then extended to investigate the possible involvement of renal alpha(1)-adrenoceptors in the interaction. Blockade of alpha(1)-adrenoceptors by prazosin (30 nmol/L) significantly reduced the vasodilatory effect of SKF38393 and virtually abolished the CyA-induced attenuation of SKF38393 responses. Further, CyA failed to alter SKF38393 vasodilations when the renal tone was raised with prostaglandin F-2 alpha (PGF(2 alpha)), a vasoconstrictor whose effect is independent of alpha(1)-adenoceptors. Together, these findings support earlier reports that both DA(1), and alpha(1)-receptors mediate the renal vasodilatory action of SKF38393 and suggest that CyA interacts selectively with the alpha(1)-receptor component to compromise SKF38393 responses.