Prostaglandin E1-induced vasorelaxation in porcine coronary arteries

The mechanism of prostaglandin E1 (PGE1)-induced vasorelaxation was studied in the porcine left anterior descending artery (diameter = 2.0-3.0 mm) and its branches (diameter = 0.6-1.0 mm). In the large coronary arteries, PGE1 increased the basal tone at concentrations from 10(-8) to 3 x 10(-7) M and decreased the tone at concentrations above 3 x 10(-7) M. However, in the small coronary arteries, PGE1 did not affect the basal tone at concentrations below 3 x 10(-6) M and evoked only relaxation at above 10(-5) M. PGE1 caused dose-dependent relaxation of vessels previously contracted by prostaglandin F2 alpha or endothelin-1 at concentrations above 10(-7) M in large coronary arteries and above 10(-8) M in small coronary arteries. Removal of the endothelium did not influence the relaxant response to PGE1 of either type of artery. In addition, 10(-4) M aspirin did not influence the PGE1-induced vasorelaxation of large and small coronary arteries. However, treatment with 5 x 10(-6) M ouabain or partial replacement of Na+ with Li+ (Na+ concentration, 25 mEq/l) significantly attenuated the relaxant response to PGE1 in large and small coronary arteries. These results indicate that the responsiveness of large and small coronary arteries to PGE1 differs in the pig and that the electrogenic Na+ pump has a primary role in the relaxant effect of PGE1 on both small and large arteries.