Vasoconstrictor responses to ATP were enhanced in a concentration-dependent-manner by endothelin-1 (0.1-1 nM) in isolated perfused segments of rabbit ear artery. Higher concentrations of endothelin-1 (3-10 nM) also enhanced vasoconstrictor responses to ATP. The enhancement of ATP responses by endothelin-1 (0.1-10 nM) was not affected by nicardipine (10 nM). The ATP-mediated component of the vasoconstrictor response to perivascular nerve stimulation in the rabbit jejunal artery was enhanced by endothelin-1 to a similar extent as that to exogenously administered ATP. The enhancement of vasoconstrictor responses to neurogenic ATP was also not affected by nicardipine.