Regular article
Xanthine oxidase activity in the dexamethasone-induced hypertensive rat

https://doi.org/10.1016/S0026-2862(03)00019-0Get rights and content

Abstract

Hypertension may be associated with an increase in oxidative stress as a possible mechanism for the increased vascular tone and organ injury. Previously, we reported an increased production of reactive oxygen species and endothelial cell death in the microcirculation of hypertensive rats. We hypothesize that xanthine oxidase (XO) may be a potential source of oxidants induced by glucocorticoid-induced hypertension. Male Wistar rats were administered dexamethasone (0.5 mg/kg/day) for 5 days to induce hypertension. After general anesthesia, cremaster muscle was collected for analysis of XO and xanthine dehydrogenase (XDH) activities. The mean blood pressure and XO levels in cremaster muscle were significantly increased in the dexamethasone-treated rats compared with controls. There was a strong age-dependent rise in total XO + XDH activity in all groups. To inhibit XO, we administered allopurinol (ALLO, 0.4 mg/mL) in the drinking water to a subset of control and dexamethasone-treated rats during a 5-day treatment. The ALLO significantly reduced the mean arterial blood pressure in the dexamethasone-treated rats. Although in the cremaster muscle the total XO + XDH levels were not completely reduced with ALLO, the XO levels of the dexamethasone-treated + ALLO rats were reduced to levels of the control + ALLO group. These results suggest that dexamethasone induces an elevated level of XO activity in the cremaster muscle. The enhanced XO activity can be attenuated by chronic allopurinol treatment.

Introduction

Increasing evidence suggests that reactive oxygen species may be involved in the hypertensive syndrome Nakazono et al 1991, Kumar and Das 1993, Grunfeld et al 1995, Suzuki et al 1995a, Saruta 1996, Swei et al 1997, Newaz and Nawal 1998, Schnackenberg et al 1998. Superoxide spontaneously reacts with nitric oxide, an ever-present vasodilator. Thus, the overabundance of superoxide through annihilation of nitric oxide may lead to arteriolar constriction and elevated resistance Grunfeld et al 1995, Vega et al 1995, Tschudi et al 1996, Kerr et al 1999, McIntyre et al 1999.

Among several mechanisms, xanthine oxidase may be a potential source for the enhanced oxidative stress. Xanthine oxidoreductase (XOR) can exist in two different forms, xanthine dehydrogenase (XDH) or xanthine oxidase (XO). XDH normally reduces NAD+, while XO accepts an electron from oxygen. Thus, XO generates superoxide and hydrogen peroxide (Fridovich, 1970; Lacy et al., 1998a). The predominant XDH form can be converted into XO under severe conditions, such as ischemic injury, and thereby cause increased oxidative stress (McCord, 1985).

In normotensive individuals, mean arterial blood pressure was reported to have a positive correlation with XO activity and uric acid concentration (Newaz et al., 1996). Hypertensive patients have higher plasma rates of hydrogen peroxide production than controls, which can be inhibited by addition of allopurinol, an XO inhibitor Lacy et al 1998a, Lacy et al 1998b. Mesenteric XO is increased in the spontaneously hypertensive rat (SHR) compared with its normotensive control, the Wistar Kyoto (WKY) rat (Suzuki et al., 1998).

Furthermore, glucocorticoids are known to participate in blood pressure regulation and in hypertension Saruta 1996, Schimmer and Parker 1996, Walker et al 1996. Adrenalectomy normalizes the blood pressure of the SHR Suzuki et al 1995b, Lim et al 2001. Dexamethasone induces XDH/XO activity and gene expression in bovine epithelial cells (Pfeffer et al., 1994). The superoxide anion, generated by XO, may react with nitric oxide, resulting in increased vasoconstriction as well as production of peroxynitrite. Dexamethasone can also block inducible nitric oxide synthase gene expression at the transcriptional level (Kanno et al., 1994). Thus, dexamethasone can act by way of several pathways to deplete the supply of nitric oxide and thereby lead to enhanced arteriolar vasoconstriction.

In light of this evidence, we hypothesize that an elevated XO activity may be a source for the oxygen free radicals in glucocorticoid-induced hypertension. To examine this hypothesis, the levels of XO activity in cremaster muscle were determined in a glucocorticoid-induced model of hypertension. In addition, the XO inhibitor, allopurinol, was administered in an attempt to determine the effects of XO as a source of reactive oxygen species.

Section snippets

Animals and dexamethasone administration

Male Wistar rats (200–300 g, Charles River Breeding Laboratories, Wilmington, MA) were maintained on a diet of standard rat chow (0.9% NaCl) and water ad libitum. The rats were divided into two age-matched groups. The experimental group was given daily injections of water-soluble dexamethasone (0.5 mg/kg of body weight for 5 days i.m.; Sigma Chemical Co., St. Louis, MO, in Plasma-Lyte, Baxter, McGaw Park, IL; pH = 7.4). This dose is sufficient to elevate blood pressure in the adrenalectomized

Blood pressures

During local and general anesthesia the mean arterial blood pressure (MBP) varied considerably and was therefore examined at several time points during the experiment (Fig. 1A). At all times, the dexamethasone-treated group had significantly elevated MBP compared with controls (P < 0.02). Addition of allopurinol served to significantly reduce the MBP (Fig. 1B). The dexamethasone-treated group had significantly reduced MBPs in the presence of allopurinol, measured in conscious rats under local

Xanthine oxidase in hypertension

In line with the current results, several studies have suggested that XO activity is enhanced in hypertensives Newaz et al 1996, Higuchi et al 1998, Laakso et al 1998, Suzuki et al 1998. The elevation of the XO activity is clearly detectable in a representative skeletal muscle, an organ that makes a major contribution to the elevation of vascular resistance (Zweifach et al., 1981). Furthermore, the current evidence indicates that the XO activity in cremaster muscle is under the control of

Acknowledgements

Supported by NIH Grant HL-10881.

References (59)

  • J.F. Valentine et al.

    Glucocorticoids repress basal and stimulated manganese superoxide dismutase levels in rat intestinal epithelial cells

    Gastroenterology

    (1994)
  • K. Aoki et al.

    Pathological studies on the endocrine organs of the spontaneously hypertensive rat

    Jpm. Heart J.

    (1963)
  • F.A. De Lano et al.

    Anesthesia and microvascular dynamics in spontaneously hypertensive rats

    Am. J. Physiol.

    (1981)
  • T. Fukui et al.

    p22phox mRNA expression and NADPH oxidase activity are increased in aortas from hypertensive rats

    Circ. Res.

    (1997)
  • S. Grunfeld et al.

    Role of superoxide in the depressed nitric oxide production by endothelial cells from genetically hypertensive rats

    Hypertension

    (1995)
  • M. Handa et al.

    Dexamethasone hypertension in rats: role of prostaglandins and pressor sensitivity to norepinephrine

    Hypertension

    (1984)
  • Y. Higuchi et al.

    Preventive effects of Shichimotsu-koka-to on renal lesions in stroke-prone spontaneously hypertensive rats

    Biol. Pharm. Bull.

    (1998)
  • P.M. Hutchins et al.

    Observation of a decreased number of small arterioles in spontaneously hypertensive rats

    Circ. Res.

    (1974)
  • K. Kanno et al.

    Regulation of inducible nitric oxide synthase gene by interleukin-1 beta in rat vascular endothelial cells

    Am. J. Physiol.

    (1994)
  • S. Kerr et al.

    Superoxide anion production is increased in a model of genetic hypertension: role of the endothelium

    Hypertension

    (1999)
  • C.Y. Kim et al.

    Analysis of circadian variation of blood pressure and heart rate in dexamethasone-induced hypertensive rats

    Clin. Exp. Hypertens.

    (1996)
  • M. Konagaya et al.

    Blockade of glucocorticoid receptor binding and inhibition of dexamethasone-induced muscle atrophy in the rat by RU38486, a potent glucocorticoid antagonist

    Endocrinology

    (1986)
  • K.V. Kumar et al.

    Are free radicals involved in the pathobiology of human essential hypertension?

    Free Radic. Res. Commun.

    (1993)
  • J. Laakso et al.

    Increased kidney xanthine oxidoreductase activity in salt-induced experimental hypertension

    Hypertension

    (1998)
  • F. Lacy et al.

    Plasma hydrogen peroxide production in hypertensives and normotensive subjects at genetic risk of hypertension

    J. Hypertens.

    (1998)
  • M. Li et al.

    Dexamethasone-induced hypertension in the rat: effects of L-arginine

    Clin. Exp. Pharmacol. Physiol.

    (1997)
  • H.H. Lim et al.

    Life and cell death labeling in the microcirculation of the spontaneously hypertensive rat

    J. Vasc. Res.

    (2001)
  • J.M. McCord

    Oxygen-derived free radicals in postischemic tissue injury

    N. Engl. J. Med.

    (1985)
  • M. McIntyre et al.

    Endothelial function in hypertension: the role of superoxide anion

    Hypertension

    (1999)
  • Cited by (0)

    View full text