REGIONAL DIFFERENCES IN NITRIC OXIDE-DEPENDENT VASCULAR-RESPONSES TO SOMATOSTATIN

The mechanisms of the vascular effects of somatostatin (ST) are not we ll known. This study compares the direct effects of ST in different va scular regions and species Isolated perfused segments of the cat super ior mesenteric artery in vitro did not exhibit a vascular response in the resting state, however, ST-induced vasodilatation was observed wit h norepinephrine preconstriction. In contrast, ST only slightly dilate d superior mesenteric vein segments In the artery, N-G-nitro-L-arginin e inhibited both ST and endothelium-dependent nitric oxide (NO) mediat ed response. No regular dose-response curves were found when ST was ap plied on the large mesenteric: artery in the cat, but rings of small m esenteric artery from both cats and dogs exhibited dose-dependent rela xations These effect were also NO-dependent. Local application of ST o n the rat saphenous artery in situ elicited NO-mediated dose-dependent vasodilatation. However, ST constricted rat saphenous veins in the ca se of either adventitial or intraluminal application. It is concluded that ST exerts different actions on the arterial and the venous vessel walt The major response in arteries is endothelium-mediated vasodilat ation seen in various species and vascular beds Large and small arteri es respond differently to ST but these differences require further elu cidation.