ROLE OF ENDOTHELIUM DERIVED RELAXING FACTOR IN THE REGULATION OF THE TONE OF THE VENOUS SYSTEM

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[Purpose]Dopamine has been widely used for the treatment of congestive heart failure, However, effects of dopamine on the vascular system have not yet been fully clarified. In this study, we investigated whether the constriction of the canine isolated femoral arterie and veins are modified by the endothelium derived relaxing factor (EDRF) which is released via the stimulation of alpha2 -adrenoceptors in the endothelium.[Method]Canine isolated femoral arteries and veins which were cut into 5 mm long ring segments with and without endothelium were suspended in 37ﾟC Krebs-Henseleit solution, and the changes in isometric force were recorded.[Results and Discussion](1)alpha2-agonist, clonidine (1X10 - 1X10 M) constricted only the veins, but not the arterles. Pretreatment with NOS inhibitor, NG-nitro-L-arginine (L-NA : 1X10 M) potentiated the constriction of the vein, but not of the arteries, exerted by clonidine, suggesting that this potentiation of the construction of the veins was mediate … More d through the production of EDRF via the activation of alpha2-adrernoceptors. (2) Dopamine (1X10 - 1X10 M) constricted both the arterie and veins. This constriction was potentiated by the pretreatment with L-NA (1X10 M), suggesting that dopamine releases EDRF in both the arteries and veins. (3) Removal of endothelium potentiated the dopamine-induced constriction of the arteries and veins, however, after the pretreatment with L-NA (1X10 M), this constriction was not observed.(4) Dopamine constricted the veins, although pretreatment with alpha2-antagonist, yohimbine((1X10 M) partially inhibited the constriction of the vein exerted by dopamine. Pretreatment with both yohimbine and L-NA did not affect the constriction of the vein exerted by dopamine. Pretreatment with yohimbine or both yohimbine and L-NA did not affect the constriction of the arteries exerted by dopamine. These results suggest that dopamine constricts both the arteries and veins and that this constriction is modified by the vasodilatory action of EDRF released via the activation of alpha2-adrenoceptors.[Conclusion]It is suggested that dopamine releases EDRF via the activation of alpha2-adrenoceptors on the endothelium in the canine isolated femoral arteries and veins. Less