Difference in Effects of Stretch on Depressive Effect of Endothelium-Derived Nitric Oxide on Noradrenaline- and High-K^+-Induced Contractions between the Aortae from Normotensive and Spontaneously Hypertensive Rats

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Difference in effects of stretch tension on endothelium-derived nitric oxide (EDNO)-dependent depression of noradrenaline (NA)- and high-K^+-induced contraction between the aortae from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) was studied. NA-induced contraction in preparations both from WKY and SHRSP was augmented in the presence of N^ω-nitro-L-arginine (L-NNA). This augmentation was minimized when the spontaneous tone, which was more prominent in preparations from SHRSP, was subtracted and the effects of L-NNA became less prominent in preparations from SHRSP. The effects of L-NNA were maximal at the stretch tension of 15 mN and, then, decreased as stretch tension increased in both preparations when the spontaneous tone was subtracted. The effects of L-NNA were less prominent when the contraction was initiated by high-K^+, although the effects of stretch on high-K^+-induced contraction were similar to that of NA-induced contraction. These results suggested 1) that both NA- and high-K^+-induced contractions are depressed by EDNO, 2) that the release of EDNO induced by high-K^+ is less than that by NA, 3) that increase in stretch tension decreases the release of EDNO, and 4) that the depressive effect of EDNO on contraction is impaired in the aorta of SHRSP.
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