Involvement of endothelial thromboxane A2 in the vasoconstrictor response induced by 15-E2t-isoprostane in isolated human umbilical vein

Abstract

The present study was undertaken to evaluate the contractile response of several E- and F-ring isoprostanes (IsoP) in human umbilical vein (HUV) and to investigate the role of the endothelium on the effect of 15-E2t-IsoP, the most potent vasoconstrictor isoprostane, in human vessels. HUV rings with or without endothelium were suspended in an organ bath for recording the isometric tension in response to different agonists. The inhibitors to be evaluated were applied 30 min before the addition of the agonist. All of the compounds tested produced concentration-dependent contractions when tested on HUV rings with endothelium. Although these compounds were equieffective, significant differences were observed in their potency, with U46619 being the most potent followed by 15-E2t-IsoP > 15-E1t-IsoP = 15-F2t-IsoP > 15-F1t-IsoP = 9-epi-15-F2t-IsoP in descending rank order of potency. 15-E2t-IsoP was the most potent of the isoprostanes evaluated and, therefore, the one employed in the present study. When intact endothelium HUV rings were used, 15-E2t-IsoP-induced contraction was unaffected by the endothelin-converting enzyme inhibitor, phosphoramidon (10 microM), suggesting that short-term endothelin-1 release is not involved in this response. However, the non-selective cyclooxygenase (COX) inhibitor, indomethacin (10 and 30 microM), and the COX-2 selective inhibitor, NS-398 (3, 10 and 30 microM) produced inhibitory effects on 15-E2t-IsoP-induced contraction of HUV rings with endothelium. These results indicate that COX-derived contractile prostanoids are involved in this effect. Furthermore, the apparent pKb values estimated for indomethacin (5.5) and NS-398 (5.4) suggest that the prostanoids involved are derived from the COX-2 isoenzyme pathway. On HUV rings with endothelium, the phospholipase A2 inhibitor, oleyloxyethyl phosphorylcholine (30 and 100 microM), induced an inhibitory effect on 15-E2t-IsoP-induced contraction, suggesting that the phospholipase A2 pathway is also involved in this effect. In addition, the thromboxane A2 synthase inhibitor furegrelate (10 and 30 microM) also inhibited 15-E2t-IsoP-induced contraction of HUV rings with endothelium, indicating that thromboxane A2 is one of the contractile prostanoids involved in this response. Endothelium denudation clearly diminished the vasoconstrictor potency of 15-E2t-IsoP, demonstrating that the endothelium releases a vasoconstrictor factor in response to 15-E2t-IsoP. The absence of an inhibitory effect at the highest concentration of furegrelate (30 microM) on 15-E2t-IsoP-induced contraction of HUV rings without endothelium suggested that endothelium is the source of thromboxane A2. We conclude that prostanoids derived from the COX-2 isoenzyme pathway participate in 15-E2t-IsoP-induced vasoconstriction of isolated HUV rings. Our results also indicate that endothelial thromboxane A2 is one of the prostanoids involved in this effect.

Role of Prostanoid Production and Receptors in the Regulation of Retinal Endogenous Amino Acid Neurotransmitters by 8-Isoprostaglandin E2, Ex Vivo

“…However, it is now well established that these autacoids also exert powerful biological effects in various biological systems [5][6][7][8][9][10][11][12]. For instance, the vasoconstrictive effect of IsoPs has been demonstrated in rats, guinea pig, human and pig bronchioles [5,6,8,12].…”

“…The vasoconstrictive effect of 8-iso-PGE 2 in human umbilical vein was reversed by both COX-inhibitors, indomethacin and NS-398 and the Tx-synthase inhibitor, furegrelate [12]. In bovine retina, the inhibitory effect of 8-isoPGE 2 on [ 3 H]dopamine release was reversed by the non-selective COX-enzyme inhibitor, flurbiprofen [19], in vitro.…”

“…There is evidence that IsoPs can produce pharmacological actions in various biological systems both in vitro and in vivo [5][6][7][8][9]. Indeed, one of the prominent and well-studied IsoPs, 8-isoprostaglandin E 2 (8-isoPGE 2 ) derived in vivo [10] has been reported to be a potent constrictor in rat, guinea pig, human and pig airways [5], rat fundus and guinea pig ileum [11] and in various vascular beds, including piglet retinal vessels [6], pig cerebral microvasculature [8] and human umbilical veins [12]. Furthermore, 8-isoPGE 2 has been shown to modulate prejunctional acetylcholine [13] and norepinephrine release [14] in isolated guinea pig trachea cells and rat stomach, respectively.…”

“…There is evidence that COX [12] and thromboxane (Tx) synthase [6,12] enzymes are involved in the actions of 8-isoPGE 2 in various tissues. The vasoconstrictive effect of 8-iso-PGE 2 in human umbilical vein was reversed by both COX-inhibitors, indomethacin and NS-398 and the Tx-synthase inhibitor, furegrelate [12].…”

Effects of cyclooxygenase inhibition on cardiovascular function in a hypercholesterolemic swine model of chronic ischemia

“…Selective COX-2 inhibition likely primarily inhibits thromboxane release, shifting the prostanoid balance in ischemic myocardium to favor prostacyclin, resulting in improved microvessel relaxation, decreased contraction, and increased perfusion. Recent studies suggest that thromboxane A 2 is produced not only by platelets but also in endothelium, where COX-2 inhibition may also regulate it (10). Additional studies have reported vasodilatory effects of COX-2 inhibitors in other vascular beds as well (8), which would be unlikely if these drugs solely inhibited prostacyclin production.…”