Endothelium-dependent relaxation to poly-L-arginine in canine coronary arteries

The endothelium-dependent relaxation elicited by poly-L-arginine was investigated in canine coronary arteries. Poly-L-arginine (10^-11 to 10^-7 M) induced concentration-dependent endothelium-dependent relaxation in segments of canine coronary arteries incubated with indomethacin. In the presence of indomethacin, arteries contracted with prostaglandin F2α and exposed also to ouabain, oxyhemoglobin, or N^ω-nitro-L-arginine, as well as those contracted with 20 mM of KCl, presented reduced endothelium-dependent relaxation to poly-L-arginine. The combination of N^ω-nitro-L-arginine with indomethacin produced further reduction of endothelium-dependent relaxation in arteries contracted with prostaglandin F2α as well as in arteries contracted with 20 mM of KCl. However, only quinacrine or calmidazolium, both in presence of N^ω-nitro-L-arginine plus indomethacin, abolished the endothelium-dependent relaxation elicited by poly-L-arginine. The relaxation to poly-L-arginine was not significantly affected by glybenclamide. The present study demonstrates that in addition to the prostacyclin and nitric oxide-dependent mechanisms, poly-L-arginine also elicits endothelium-dependent relaxation in canine coronary arteries, stimulating the release of endothelial relaxing factor (s) produced by the phospholipase A2 pathway, but independent of the cyclooxygenase pathway, which may cause hyperpolarization of the vascular smooth muscle.