Yoshio Iwama

Prostaglandin H2 may be the endothelium-derived contracting factor released by acetylcholine in the aorta of the rat.

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 A2/prostaglandin H2 receptor antagonist (ONO-3708) in aortic rings from both SHR and WKY rats. A thromboxane A2 synthetase inhibitor (OKY-046) did not affect the acetylcholine-induced relaxation in the aortic rings from SHR or WKY rats. In the organ bath solution, after acetylcholine stimulation, prostaglandin E2 and 6-keto-prostaglandin F1 alpha concentrations increased but not prostaglandin F2 alpha and thromboxane B2 concentrations. Exogenous prostaglandin H2, a stable analogue of thromboxane A2, and prostaglandin F2 alpha induced contractions of the SHR rings at a lower concentration than prostaglandin E2, prostaglandin D2, and prostaglandin I2. 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 endothelium-derived 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 H2, a precursor of the released prostaglandins, is a strong candidate for endothelium-derived contracting factor produced by acetylcholine stimulation.

Prostaglandin H2 as an endothelium-derived contracting factor and its interaction with endothelium-derived nitric oxide.

The possibility that prostaglandin H2 is an endothelium-derived contracting factor (EDCF) was evaluated in rings of thoracic aorta of spontaneously hypertensive rats (SHR). When the aortic rings were contracted with norepinephrine (10(-7) mol/l) and treated with acetylcholine (10(-5) mol/l), a relaxant response with a peak after approximately 1 min and a contractile response with a peak after approximately 7 min were observed. When these rings were pretreated with a thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708), the later contractile response was clearly inhibited and only a sustained relaxant response was observed. This relaxant response was completely inhibited by pretreatment with an inhibitor of nitric oxide production (N-nitroarginine methylester; NNM). When aortic rings in the basal condition were treated with NNM and then with acetylcholine, a contractile response with a peak after 7 min was observed, but this reaction was completely inhibited by pretreatment with ONO-3708. The rate of 6-keto-prostaglandin F1 alpha production showed a peak of 1.4 x 10(-6) mol/l per min per tissue, 2-4 min after administration of acetylcholine. With exogenous prostaglandin H2 (5 x 10(-7) mol/l), a peak contraction was observed after approximately 4 min, the degree and pattern of which were similar to that induced by acetylcholine. Endogenous prostaglandin H2 is considered to be produced by the aortic rings in an amount sufficient to induce vascular contraction within 30 s, and the pattern of this contraction induced by acetylcholine resembles that induced by exogenous prostaglandin H2. These findings most strongly suggest that prostaglandin H2 is an EDCF.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation with blood pressure of the acetylcholine-induced endothelium-derived contracting factor in the rat aorta.

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 Wistar-Kyoto rats at 5, 10, 20, and 30 weeks of age. In norepinephrine-precontracted rings, acetylcholine (10(-8) to 10(-5) M)-induced relaxations diminished at the doses of 10(-6) to 10(-5) M in both strains except at 5 weeks of age. Treatment with a thromboxane A2/prostaglandin H2 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, NG-nitro-L-arginine methyl ester. In aorta treated with NG-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 A2 synthetase inhibitor (OKY-046). There was a statistically significant correlation between the acetylcholine-induced contractions and blood pressure. Release of 6-ketoprostaglandin F1 alpha by acetylcholine from the aorta was greater in spontaneously hypertensive rats. In vivo administration of another thromboxane A2/prostaglandin H2 antagonist (ONO-8809) (10 or 30 micrograms per body per day) for 3 weeks (5-8 weeks of age) did not affect blood pressure in either rat strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen-derived free radical-induced vasoconstriction by thromboxane A2 in aorta of the spontaneously hypertensive rat.

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.

Prostaglandin H2 as an endothelium-derived contracting factor modulates endothelin-1-induced contraction

Objective To investigate the possible involvement of prostaglandin H2, an endothelium-derived contracting factor in the rat aorta, in the development of the contraction induced by endothelin-1 Methods The aortic rings from spontaneously hypertensive rats (SHR) were prepared, and the changes of isometric tension of these rings developed by endothelin-1 were recorded with or without the treatment of several inhibitors or an antagonist. The concentrations of prostaglandins and thromboxane B2 in the bath solution with the rings contracted by endothelin-1 were measured by radioimmunoassay. The effects of a thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708) on endothelin-1-induced contraction were compared in SHR and Wistar-Kyoto (WKY) rats Results Indomethacin (10-5mol/l) and ONO-3708 (10-6mol/l) significantly diminished endothelin-1 (3×10-8mol/l)-induced contractions in the aortic rings from SHR with but not without endothelium. The thromboxane A2 synthetase inhibitors OKY-046 (10-5 mol/l) and RS-5186 (10-5mol/l) did not attenuate the contractions either with or without endothelium. Endothelin-1 significantly increased the release of 6-keto-prostaglandin F1α, which is the metabolite of prostaglandin I2 and its precursor prostaglandin H2, from rings with endothelium of SHR, but the concentration of thromboxane B2 from aortic rings was unchanged. In the rings without endothelium the endothelin-1-induced release of 6-keto-prostaglandin F1α was also observed. The half-maximal effective concentration of endothelin-1 for rings from SHR was shifted to the right by ONO-3708, but that of WKY rats was not changed, and significantly greater amounts of 6-keto-prostaglandin F1α were released in the rings from SHR than in those from WKY rats by endothelin-1 Conclusions Endothelin-1 induced the release of prostaglandin H2 from endothelial cells in the rat aorta, the effect being greater in the hypertensive state. The released prostaglandin H2, an endothelium-derived contracting factor, modulated the vasoconstriction that is induced by endothelin-1, another endothelium-derived contracting factor, in addition to the direct vasoconstrictive action of endothelin-1 on vascular smooth muscle

Regulation of Vascular Tone by Endothelium-Derived Contracting Factor (EDCF)

Our purpose was 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 the thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708) in aortic rings from both SHR and WKY rats. A thromboxane A2 synthetase inhibitor (OKY-046) did not affect the acetylcholine-induced relaxation in the aortic rings from either SHR or WKY rats. When these rings were pretreated with an inhibitor of nitric oxide production (N-nitroarginine methylester), the relaxant response induced by acetylcholine was completely inhibitied. In the organ bath solution, prostaglandin E2 and 6-keto-prostaglandin F1α concentrations increased after acetylcholine stimulation, but prostaglandin F2α and thromboxane B2 concentrations did not. Exogenous prostaglandin H2, a stable analogue of thromboxane A2, and prostaglandin F2α induced contractions of the SHR rings at a lower concentration than prostaglandin E2, prostaglandin D2, and prostaglandin I2. These contractile responses to various prostaglandins were markedly inhibited by pretreatment with ONO-3708. A prostacyclin sinthetase inhibitor did not affect the relaxant responses to acetylcholine in the SHR rings. These results show that endothelium-derived contracting factor is produced and released by acetylcholine stimulation the aorta of not only SHR but also in WKY rats, and suggest that prostaglandin H2, a precursor of the released prostaglandins, is a strong candidate for being endothelium-derived contracting factor produced by acetylcholine stimulation. It was also suggested that in the rat aorta treated by acetylcholine, the vascular tonus is regulated by two factors, prostaglandin H2 (EDCF) and nitric oxide (endothelium-derived relaxing factor).