A regional variation of acetylcholine-induced relaxation in different segments of rat aorta.

The tension of the isolated thoracic aorta of the rat was measured isometrically to determine if there is a regional variation of the relaxation to acetylcholine (ACh). Endothelium-derived nitric oxide (NO)-dependent relaxation to ACh in the thoracic aorta precontracted with norepinephrine was significantly greater in the middle and distal segments than in the proximal segments. The relaxation to ACh was inhibited by NG-nitro-L-arginine methyl ester, an inhibitor of NO synthase. The relaxation to the NO donor sodium nitroprusside did not differ between the same three segments of the thoracic aorta. These results suggest that there are regional variations in the ACh-induced release of endothelium-derived NO in the rat thoracic aorta.