The vasoactive effect of endothelin-1 applied intraluminally or extraluminally was studied in vitro in isolated perfused porcine pulpal arterioles using a microperfusion system. Pulpal arterioles (outer diameter, 94.2 +/- 2.8 mum, n = 12) were cannulated and perfused at a constant flow rate in an environment-controlled bath on the stage of an inverted microscope. The vessel diameters were measured online. Both intraluminal and extraluminal application of endothelin-1 (10(-16) M to 10(-8) M) induced dose-dependent constrictions, reaching 82.3 +/- 1.7% (n = 12) and 70.5 +/- 1.3% (n = 12) at 10(-8) M, respectively. Nifedipine reversed endothelin-1-induced constriction dose-dependently at 10(-7) M and above. These data demonstrate that endothelin-1 induces calcium-dependent vasoconstriction in porcine pulpal arterioles, with extraluminal application more potent, which seems to reflect the possible modulation of vascular endothelium in the control of vascular tone.