Presynaptic effects of dopexamine hydrochloride in the canine kidney.

The effects of dopexamine on the vasoconstrictor response to renal nerve stimulation and noradrenaline were determined in anesthetized dogs. Renal vasoconstriction was repeated during the sequential administration of iso-osmotic saline, dopexamine, dopexamine plus the DA1-dopamine receptor antagonist, SCH 23390, and dopexamine plus SCH 23390 and the DA2-dopamine receptor antagonist, domperidone. Renal nerve stimulation-induced vasoconstriction did not change with dopexamine or dopexamine plus SCH 23390, but increased with the addition of domperidone. Dopexamine also potentiated noradrenaline-induced vasoconstriction. Antagonists alone had no affect on the vasoconstrictor response to either stimulus. The findings suggest that the absence of an effect of dopexamine on neuronally-induced renal vasoconstriction was a consequence of a balance between its actions at presynaptic DA2-dopamine receptors (attenuated vasoconstriction) and its ability to inhibit the uptake1 transporter (enhanced vasoconstriction).