VARIATIONS OF ARTERIAL RESPONSES IN-VITRO IN DIFFERENT SECTIONS OF RAT MAIN SUPERIOR MESENTERIC-ARTERY

We examined the control of vascular tone in rat main superior mesenter ic artery. Three standard rings (3 mm in length) of the mesenteric art ery were cut, beginning 5 mm, 13 mm and 21 mm distally from the mesent eric artery-aorta junction. In noradrenaline-precontracted rings, rela xations to acetylcholine in the absence and presence of the cyclooxyge nase inhibitor diclofenac, did not differ in the studied sections. How ever, the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, attenuated the diclofenac-resistant responses to acetylcholine more effectively in the proximal than the distal section. Glibenclamid e, an inhibitor of ATP-sensitive K+ channels, diminished relaxations e voked by acetylcholine only in the distal section, whereas the inhibit or of Ca2+ activated K+ channels, apamin, attenuated the responses in all sections. Furthermore, relaxation sensitivity to nitroprusside and isoprenaline was lower in the proximal than distal section. Arterial contractile sensitivity to noradrenaline and potassium chloride was hi gher, while the maximal contractile force generation was lower in the proximal than the distal part. In conclusion, in different sections of rat main superior mesenteric artery considerable variability was obse rved in vasoconstrictor and vasodilator responses, as well as in the c ontribution of endothelial nitric oxide and endothelium-mediated hyper polarization to vasodilation. Therefore, the present results emphasize the fact that only corresponding vessel segments should be used when investigating the control of arterial tone.