SOMATOSTATIN INDUCES VASODILATATION IN THE CAT MESENTERIC-ARTERY VIA ENDOTHELIUM-DERIVED NITRIC-OXIDE AND PROSTAGLANDINS

Direct vascular effects of somatostatin (ST) were investigated in cat superior mesenteric artery (SMA) segments in vitro. Changes of outer d iameter were measured at constant axial length and perfusion pressure. SMA segments in the resting state were not affected by ST, regardless of endothelial integrity. Noradrenaline-preconstricted SMA segments w ere dilated concentration-dependently by ST (EC(50) 10(-13) mol/l). At maximal dilatation (by 10(-11) mol/l ST) the preconstriction was dimi nished to 45 +/- 9% (P<0.001). Perfusion with Triton X-100, or N-G-nit ro-L-arginine nearly abolished the ST-induced dilatation, while indome thacin treatment partially suppressed it. We conclude that ST dilates preconstricted cat SMA segments mainly via the endothelial release of nitric oxide, and additionally via prostaglandins.