VASORELAXANT EFFECTS OF OXPENTIFYLLINE AND THEOPHYLLINE ON RAT ISOLATED AORTA

The mechanism of the relaxation response of rat aorta to the phosphodi esterase inhibitors oxpentifylline and theophylline was studied. Oxpen tifylline induced a greater vasorelaxation response in the intact stri ps than in those without endothelium. The endothelium-dependent relaxa tion response to oxpentifylline was inhibited by nitro-L-arginine but not by indomethacin, and the endothelium-independent relaxation respon se was potentiated by the combination with isoprenaline but not sodium nitroprusside. Theophylline induced a similar relaxation response in vascular strips with and without endothelium. The relaxation response to theophylline was not inhibited by indomethacin or nitro-L-arginine in intact strips, but was potentiated by combination with isoprenaline or sodium nitroprusside in the denuded strips. These results suggest that the two phosphodiesterase inhibitors oxpentifylline and theophyll ine induce vasorelaxation by different mechanisms. Oxpentifylline can induce both endothelium-dependent relaxation, which is probably mediat ed by an endothelium-derived relaxing factor, and endothelium-independ ent relaxation, which may be due to an inhibitory action on phosphodie sterase of vascular smooth muscle. In contrast, theophylline can induc e endothelium-independent relaxation alone, without modulation by the endothelium.