tert-Butyl hydroperoxide-mediated vascular responses in DOCA-salt hypertensive rats
Introduction
tert-Butyl hydroperoxide (t-BOOH), a precursor in the formation of malondialdehyde, is a membrane-permeant oxidant that induces oxidative stress in different systems Garcia-Cohen et al., 2000, Schilling and Elliott, 1992. The compound is lipid soluble, thus it is rapidly delivered into cytosolic milieu. It is, unlike H2O2, not metabolized by catalase. t-BOOH elicits direct constriction in the aorta and reduces acetylcholine-induced relaxant responses in rat coronary vessels Yaghi and Watts, 1993, Garcia-Cohen et al., 2000.
Oxidative stress plays a critical role in pathogenesis of hypertension Rajagopalan et al., 1996, Makino et al., 2002 and other cardiovascular diseases Holvoet et al., 1995, Wang and Walsh, 1995 as well as in the vascular damage associated with aging (Rodriguez-Martinez et al., 1998). Reactive oxygen species (ROS) including superoxide anions (O2−), hydroxyl radical (OH.), as well as oxidants like hydrogen peroxide (H2O2) (Halliwell and Cross, 1994), and lipid radical species are known to play critical roles in the genesis of vascular diseases. Increased ROS activity results in the nonenzymatic production of carbonyl compounds (e.g., glyoxal, methylglyoxal, glycoaldehyde, 3-deoxyglucosone, and dehydroascorbate) and lipoperoxides which, in turn, reacts with and modify structural and functional proteins leading to formation of advanced glycation products and advanced lipoxidation products Miyata et al., 1998, Miyata et al., 2000.
Tempol (4-hydroxyl-2,2,6,6-tetramethyl-piperidine-N-oxyl), is a small molecular weight cyclic nitroxide that permeates biological membranes and can react with superoxide anion in vitro (Laight et al., 1997a) and in vivo (Cuzzocrea et al., 2000). Tempol scavenges O2− (Laight et al., 1997b), and thus prevents the toxicity associated with these radical species. This compound also reacts with lipid, lipid alkoxyl, and lipid peroxyl radicals to terminate the chain reactions associated with lipid peroxidation (Zhang et al., 1998). Tempol also scavenges hydroxyl radicals and reduces the generation of these radicals by Fenton-type reaction Monti et al., 1996, Mitchell et al., 1990.
Although oxidative stress has been implicated in hypertension (Bouloumie et al., 1997), the vasoreactivity elicited by the prooxidant, t-BOOH during hypertension remains to be characterized. The present study evaluates the vasoreactivity to t-BOOH in DOCA-salt-induced hypertension—a form of hypertension in which plasma renin activity is low (Gavras et al., 1975) thus allowing oxidative stress to be evaluated without the complications of angiotensin II. We also determined the influence of an antioxidant, tempol, on vasoreactivity to t-BOOH, as well as SOD expression during oxidative stress elicited by DOCA-salt-induced hypertension.
Section snippets
Methods
Male Sprague–Dawley rats (250–350 g) were anesthesized with pentobarbital (60 mg/kg ip). The abdominal cavity of individual rats was opened and the right kidney was cannulated through an incision at the junction of renal artery and aorta. The kidney, with its surrounding fat trimmed off, was flushed with heparinized physiological salt solution (PSS; composition in Section 2.2), and then removed for perfusion in a custom-made temperature-controlled glass chamber. Mesenteric vascular beds (MVb)
Results
The systolic blood pressure of potassium-supplemented DOCA (100 mg, 21-day release) salt (8%)-treated rats was 202.9±15.2 mm Hg (n=8) while that of age-matched sham rats that received placebo pellet was 130.4±4.8 (n=8). The blood pressure of DOCA-salt-treated rats was significantly (P<.05) higher than that of sham rats. However, the blood pressure of DOCA-salt rats treated with tempol (15 mg/kg sc) for 21 days, i.e., DOCA/TEMPOL rats, was significantly (P<.05) reduced (150.6±6.2, n=8) compared
Discussion
The organic hydroperoxide, t-BOOH, generates free radical species in vitro (Chamulitrat et al., 1991) and in vivo Athar et al., 1989, Hix et al., 2000. Free radical species cause oxidative stress (Halliwell and Cross, 1994) and their production increases during various forms of hypertension Rajagopalan et al., 1996, Somers et al., 2000. The present study documents that t-BOOH-induced vasoconstriction involves free radical species and are increased during hypertension. Our data further show that
Acknowledgements
The American Heart Association, Ohio Valley Affiliate, is gratefully acknowledged for supporting ASOA with a Grant-in-Aid award (No. 0051391B).
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