Renal vasodilation by a prostaglandin analog during dopaminergic and alpha-adrenergic blockade

The possible participation of dopaminergic and alpha-adrenergic renal vascular receptors in the renal blood flow response to a new prostaglandin (PG) analog was investigated in anesthetized dogs. Alpha-adrenergic blockade with phenoxybenzamine (POB) enhanced the renal blood flow (RBF) responses to intrarenal (ira) injections of (0.75 to 48 micrograms/kg) dopamine but not to the PG analog (0.05 to 20 micrograms/kg i.v.) or to PGE2 (0.32 to 40 ng/kg ira). In phenoxybenzamine-treated dogs, bulbocapnine, a dopamine antagonist, blocked the increases in RBF stimulated by intrarenal injections of 0.1 to 24 micrograms/kg dopamine but had no effect on the responses to 0.5 to 100 ng/kg of PGE2. When RBF was elevated to a stable plateau by treatment with the PG analog (0.05 mg/kg i.v.) or by intrarenal infusion of PGE2 (0.01 microgram/kg/min), bulbocapnine (100 micrograms/kg/min) did not alter the effects of either compound. In contrast, the effects of 6 micrograms/kg/min dopamine ira on RBF, mean arterial pressure and renal vascular resistance were reversed by bulbocapnine. We conclude that the PG analog and PGE2 increased RBF by mechanisms which were independent of dopaminergic and alpha-adrenergic pathways.