Oxidative Stress Induced by tert-Butyl Hydroperoxide Causes Vasoconstriction in the Aorta from Hypertensive and Aged Rats : Role of Cyclooxygenase-2 Isoform 1

We analyzed the mechanisms involved in the effect of tert-butyl hydroperoxide (t-BOOH) in isolated aortic rings with and without endothelium from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at 6, 18, and 24 months of age. t-BOOH (1 mM-10 mM) induced concentrationdependent contractions that were scarcely modified by aging and potentiated in SHR and by endothelium removal. The nitric oxide synthase and prostacyclin synthase inhibitors N-nitroL-arginine methyl ester (100 mM) and tranylcypromine (100 mM), respectively, increased both basal tone and the t-BOOH-induced contractions in intact segments from WKY, with these effects not observed in SHR. Indomethacin (10 mM), a nonspecific cyclooxygenase inhibitor, and SQ 29,548 (10 mM), a prostaglandin H2/thromboxane A2 receptor blocker, abolished the t-BOOH-induced vasoconstriction, independent of age and hypertension. In both strains, these contractile responses were unaltered by the thromboxane synthase inhibitor imidazole (10 mM). The cyclooxygenase-2 inhibitor NS-398 (10 mM) abolished or markedly reduced the t-BOOH-induced contractions in segments with or without endothelium, respectively. In addition, expression of cyclooxygenase-2 protein was detected in aorta from WKY and SHR in either basal condition or after stimulation with t-BOOH. These results suggest that (1) t-BOOH-induced vasoconstriction in the aorta from WKY and SHR is essentially mediated by cyclooxygenase-2 metabolites, different from thromboxane-A2, probably prostaglandin-H2, and/or isoprostanes; (2) aging scarcely modifies, whereas endothelium negatively modulates, these contractions in both strains; and (3) nitric oxide and prostacyclin exert a negative modulator role on the t-BOOH-induced vasoconstriction in WKY, with this modulator role lost in SHR. Lipid peroxidation is a free radical-dependent process that is involved in the modification of structure and permeability of membranes, age pigment formation, oxidative modification of low-density lipoproteins, and alteration of vasomotor tone regulation (Hicks and Gebicki, 1978; Kikugawa et al., 1981; Esterbauer et al., 1992; Rodrı́guez-Martı́nez et al., 1996, 1998a). Of special clinical interest is the role played by lipid peroxidation in the pathogenesis of cardiovascular diseases, such as congestive heart failure, atherosclerosis, or preeclampsia (Holvoet et al., 1995; Wang and Walsh, 1995; Dı́az-Vélez et al., 1996), as well as in the vascular damage associated with aging (Rodrı́guez-Martı́nez et al., 1998a). Thus, enhancement of lipid peroxidation derivatives in plasma or vascular tissues (Rodrı́guez-Martı́nez and Ruı́zTorres, 1992; Cester et al., 1994; Rodrı́guez-Martı́nez et al., 1998a), along with a certain degree of endothelial alteration (Marı́n, 1993, 1995; Marı́n and Rodrı́guez-Martı́nez, 1997), appears to be common findings in hypertension and aging. Oxidative stress induced by lipid peroxidation derivatives can affect the vascular reactivity modifying basal tone, the responses to agonists, Ca-signaling mechanisms, and the production, release, or effect of endothelium-derived paracrine factors (Gurtner and Burke-Wolin, 1991; Schilling and Elliott, 1992; Hubel et al., 1993; Rodrı́guez-Martı́nez et al., 1996). In this regard, we recently described that the classic marker of lipid peroxidation processes, malondialdehyde, produces an impairment of the relaxant responses evoked by acetylcholine and that the imbalance between the glutathione-dependent antioxidant system and malondialdehyde levels in blood is implicated in the dysfunction of endotheliumdependent relaxations with age (Rodrı́guez-Martı́nez et al., 1996, 1998a). Received for publication July 23, 1999. 1 This work was supported by grants from Fondo de Investigaciones Sanitarias (98/0074-02), Dirección General de Investigación Científica y Técnica (PM97-0008), Comunidad de Madrid (08.3/0003/1998), and Bayer España. ABBREVIATIONS: WKY, Wistar-Kyoto rats; SHR, spontaneously hypertensive rats; MAP, mean arterial pressure; KHS, Krebs-Henseleit solution; COX, cyclooxygenase; H2O2, hydrogen peroxide; L-NAME, N -nitro-L-arginine methyl ester; NO, nitric oxide; PG, prostaglandin; t-BOOH, tert-butyl hydroperoxide; TX, thromboxane. 0022-3565/00/2931-0075$03.00/0 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 293, No. 1 Copyright © 2000 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A. JPET 293:75–81, 2000 75 at A PE T Jornals on July 7, 2017 jpet.asjournals. org D ow nladed from A precursor in the formation of malondialdehyde is, among other hydroperoxides, tert-butyl hydroperoxide (t-BOOH), a membrane-permeant oxidant that has been extensively used as a model of oxidative stress in different systems. In the past years, considerable evidence has been accumulated to suggest that t-BOOH is able to induce changes in either Casignaling mechanisms (Schilling and Elliott, 1992; Elliott and Doan, 1993; Elliott et al., 1995) or monovalent cation homeostasis (Elliott and Schilling, 1992; Cutaia and Parks, 1994; Koliwad et al., 1996a,b) in vascular endothelial cells. Vascular reactivity can also be altered by t-BOOH. Thus, vasoconstriction can be induced by perfusing isolated rabbit lung (Gurtner and Burke-Wolin, 1991) or isolated human placental cotyledons (Walsh et al., 1993) with t-BOOH. This oxidant can also potentiate the contractile responses to potassium or norepinephrine in rat mesenteric artery (Hubel et al., 1993) or reduce the relaxant responses to acetylcholine in rat coronary vessels (Yaghi and Watts, 1993). Nevertheless, the vascular effect and the mechanism of action of t-BOOH in hypertension and aging have been scarcely studied, although in both processes oxidative stress could play a causative role (Rodrı́guez-Martı́nez and Ruiz-Torres, 1992; Bouloumié et al., 1997). Therefore, the objective of this study was to assess the influence of hypertension, age, and endothelium on the changes induced by t-BOOH on vasomotor tone in aortic rings from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at 6, 18, and 24 months of age, as well as the possible mechanisms involved. Materials and Methods This study was performed in 36 WKY and 36 SHR male rats at ages 6, 18, and 24 months, which were born and fed with regular chow at the facilities of the Facultad de Medicina of the Universidad Autónoma of Madrid. The procedures were in accord with the National Institutes of Health Guide for the Care and Use of Laboratory