The present experiment was performed to identify endothelium-derived contracting factor produced by acetylcholine stimulation in the aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. The rings of the thoracic aorta were obtained from age-matched SHR and WKY rats, and changes in isometric tension were recorded. The relaxant responses to acetylcholine in the aortic rings from SHR were significantly weaker than those from WKY rats. The relaxant responses to acetylcholine were significantly enhanced by pretreatment with a cyclooxygenase inhibitor (indomethacin) or thromboxane A 2 / prostaglandin H 2 receptor antagonist (ONO-3708) in aortic rings from both SHR and WKY rats. A thromboxane A 2 synthetase inhibitor (OKY-046) did not affect the acetylcholineinduced relaxation in the aortic rings from SHR or WKY rats. In the organ bath solution, after acetylcholine stimulation, prostaglandin E 2 and 6-keto-prostaglandin F la concentrations increased but not prostaglandin F 2a and thromboxane B 2 concentrations. Exogenous prostaglandin H 2 , a stable analogue of thromboxane A 2 , and prostaglandin F 2a induced contractions of the SHR rings at a lower concentration than prostaglandin E 2 , prostaglandin D 2 , and prostaglandin I 2 . These contractile responses to various prostaglandins were markedly inhibited by pretreatment with ONO-3708. A prostacyclin synthetase inhibitor did not affect the relaxant responses to acetylcholine in the SHR rings. These results show that endotheliumderived contracting factor is produced and released by acetylcholine stimulation not only in the aorta of SHR but also in those of WKY rats and suggest that prostaglandin H 2 , a precursor of the released prostaglandins, is a strong candidate for endothelium-derived contracting factor produced by acetylcholine stimulation. (Hypertension 1990;15:475-481) A ll blood vessels are lined by the endothelium, and the important role of an organic or functional abnormality of endothelial cells in the pathogenesis and pathophysiology of various diseases has attracted attention.In 1980, Furchgott et al 1 found that acetylcholine induced endothelium-dependent relaxation in the rabbit aorta. Since then, various substances have been reported to induce endothelium-dependent relaxation in most of the blood vessels in mammals. 23Several pharmacological observations have strongly suggested that there is more than one endothelium-

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To examine a relation between the production of acetylcholine-induced endothelium-derived contracting factor and an increase in blood pressure, endothelium-dependent contraction and relaxation were evaluated by measuring the isometric tension of aortic rings from spontaneously hypertensive rats and Wlstar-Kyoto rats at 5,10, 20, and 30 weeks of age. In norepinephrine-precontracted rings, acetylcholine (10"' to 10"' M)-induced relaxations diminished at the doses of 10"' to 10" 5 M in both strains except at 5 weeks of age. Treatment with a thromboxane A 2 /prostaglandin H 2 antagonist (ONO-3708) prevented this reduction in acetylcholine-induced relaxations in both strains and induced dose-dependent relaxations, which were completely inhibited by treatment with a nitric oxide inhibitor, A rG -nitro-L-arginine methyl ester. In aorta treated with /V G -nitro-L-arginine methyl ester without precontraction, acetylcholine induced dose-dependent contractions, which were greater in spontaneously hypertensive rats than in Wistar-Kyoto rats. These acetylcholine-induced contractions, which were observed only in rings with endothelium, were completely inhibited by treatment with ONO-3708 but not with a thromboxane A 2 synthetase inhibitor (OKY-046). There was a statistically significant correlation between the acetylcholine-induced contractions and blood pressure. Release of 6-ketoprostaglandln F, o by acetylcholine from the aorta was greater in spontaneously hypertensive rats. In vivo administration of another thromboxane A 2 /prostaglandin H 2 antagonist (ONO-8809) (10 or 30 /ig per body per day) for 3 weeks (5-8 weeks of age) did not affect blood pressure in either rat strain. These results suggest that the production of acetylcholine-induced endothelium-derived contracting factor, which is most likely prostaglandin H 2 , is closely associated with the increase in blood pressure that occurs in young to adult rats. (Hypertension 1992;19-J26-332) KEY WORDS • endothelium • endothelium-derived contracting factor • endothelium-derived relaxing factor • prostaglandin H 2 • spontaneously hypertensive rats T he endothelium produces various vasoactive substances and controls vascular smooth muscle tone. Since Furchgott and Zawadzki 1 first reported the presence of endothelium-derived relaxing factor (EDRF) in 1980, many vessels were found to produce EDRF in response to a variety of stimuli. -3The primary component of EDRF was thereafter shown to be nitric oxide. 4 ' 5 It was also clarified that endothelium-derived contracting factor (EDCF) is also produced by stimulated vessels, 6 and increased production of EDCF has been reported in anoxia, 7 hypertension, 8 and aging. 9 The nature of EDCF varies with the species and the anatomical site of its production, but thromboxane A 2 (TXA 2 ), 10 superoxide anion, 1112 endothelin, 13 and prostaglandin H 2 (PGH 2 ) 14 have been suggested as EDCF. The EDCF released from the rat thoracic aorta by acetylcholine stimulation is likely to be PGH 2 , as we have previously suggested.14 From the ...

This study was performed to clarify the mechanism of vasoconstriction induced by oxygen-derived free radicals in spontaneously hypertensive rats. The isometric tension of aortic rings from spontaneously hypertensive rats and Wistar-Kyoto rats was measured in Krebs-Henseleit solution. Oxygen-derived free radicals were generated by mixing xanthine and xanthine oxidase. The removal of endothelium enhanced the contractions induced by oxygen-derived free radicals. The inhibition of nitric oxide production with NG-nitro-L-arginine methyl ester (10(-4) M) enhanced the contractions. Treatment with the thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (10(-4) M) or RS-5186 (10(-4) M) markedly reduced the contractions. Treatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist, ONO-3708 (10(-6) M), completely abolished the oxygen-derived free radical-induced contractions. In contrast, treatment with the PGI2 synthetase inhibitor tranylcypromine (10(-4) M) did not attenuate the oxygen-derived free radical-induced contractions. Whether endothelium was present or not, the release of TXB2, PGE2, and 6-keto-PGF1alpha, but not PGF2alpha, was increased by the production of oxygen-derived free radicals. Catalase and the hydroxyl radical scavenger deferoxamine plus mannitol markedly inhibited the oxygen-derived free radical-induced contractions. These results suggest that oxygen-derived free radical-induced vasoconstriction in spontaneously hypertensive rat aorta is caused by TXA2 and PGH2 released in smooth muscle.

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