Abstract
The effects of intraluminal and extraluminal endothelin-1 and its interactions with endothelium-derived relaxing factor were studied in perfused mesenteric resistance arteries of Wistar-Kyoto rats and spontaneously hypertensive rats. Changes in intraluminal diameter were recorded. In adult Wistar-Kyoto rats, but not spontaneously hypertensive rats, low concentrations of intraluminal endothelin-1 (10(-10) to 10(-9) M) caused relaxations of quiescent arteries blocked by indomethacin. After endothelial removal, intraluminal endothelin-1 evoked concentration-dependent contractions in both strains. Extraluminal endothelin-1 caused greater contractions of arteries with endothelium than intraluminal endothelin-1, and the sensitivity was lower in adult hypertensive rats; endothelial removal enhanced the contractions to extraluminal endothelin-1 to a greater extent in hypertensive than in normotensive rats. In arteries without endothelium, intraluminal and extraluminal endothelin-1 caused comparable contractions, but the sensitivity was reduced in adult but not young hypertensive as compared with normotensive rats. Both young spontaneously hypertensive and normotensive rats exhibited a high sensitivity to the peptide. In arteries precontracted with endothelin-1, endothelium-dependent relaxation to intraluminal acetylcholine was reduced in hypertensive as compared with normotensive rats, whereas relaxations to extraluminal acetylcholine were increased in hypertensive rats. Thus, endothelin-1 interacts with both vascular smooth muscle and the endothelium. The sensitivity of vascular smooth muscle to endothelin-1 is reduced in adult hypertensive rats. Intraluminal activation of the endothelium by endothelin-1 or acetylcholine is reduced in spontaneously hypertensive rats, whereas extraluminal activation causes more pronounced responses in hypertensive than in normotensive rats, suggesting a prominent dysfunction of the intraluminal surface of the endothelium in hypertension.
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