Uric acid does not affect the acetylcholine-induced relaxation of aorta from normotensive and deoxycorticosterone acetate-salt hypertensive rats

Abstract

Uric acid (UA) results from xanthine oxidase (XO) catabolism of xanthine and is the final product of purine catabolism in humans. In this species, hyperuricemia is associated with gout, nephropathy, and increased cardiovascular disease risk. Although the effects of hyperuricemia in vascular biology are overall controversial, UA has been described as an antioxidant and as potentially improving endothelial function. Hypertension is associated with endothelial dysfunction. We hypothesized that UA improves the endothelial function of aorta from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. UA (100 microM) in the presence of the uricase inhibitor oxonic acid (10 microM) did not modify relaxation to acetylcholine (ACh) (1 nM-10 microM) in the aorta from nontreated, sham normotensive, and DOCA-salt hypertensive rats [response to 10 microM ACh for UA versus vehicle, respectively: nontreated = 37 +/- 7 versus 48 +/- 7%, sham = 53 +/- 15 versus 57 +/- 20%, DOCA = 81 +/- 4 versus 85 +/- 2% from 20 microM prostaglandin 2alpha (PGF(2alpha))-induced contraction]. Allopurinol (100 microM), a XO inhibitor, did not significantly alter the ACh-induced relaxation of sham and DOCA aortic rings (response to 10 microM ACh for allopurinol versus vehicle, respectively: sham = 61 +/- 5 versus 68 +/- 9%, DOCA = 87 +/- 6 versus 88 +/- 3% from 20 microM PGF(2alpha)-induced contraction). Uricemia, ranging from unmeasurable to 547 microM in sham and to 506 microM in DOCA rats, was not significantly different between these two groups. The expression and activity of XO, as well as the expression of uricase, were not different between sham and DOCA rat aorta. We conclude that, at least in vitro, UA does not affect the ACh-induced relaxation of normotensive and DOCA-salt hypertensive rats.

Fig. 1.

Cumulative concentration-response curves to ACh (10⁻⁹–10⁻⁵ M) of endothelial-intact aorta rings from nontreated rats in the presence of vehicle (closed symbols) or uric acid (100 μM) plus oxonic acid (10 μM) (open symbols). RA, rat aorta. Points represent means ± S.E.M. percentage of contraction induced by 20 μM PGF_2α for the respective N.

Fig. 2.

Cumulative concentration-response curves to ACh (10⁻⁹–10⁻⁵ M) of aorta rings from sham normotensive (circles) and DOCA-salt hypertensive rats (squares) in the presence of vehicle (closed symbols) or uric acid (100 μM) plus oxonic acid (10 μM) (open symbols). RA, rat aorta. Points represent means ± S.E.M. percentage of contraction induced by 20 μM PGF_2α for the respective N.

Fig. 3.

Cumulative concentration-response curves to ACh (10⁻⁹–10⁻⁵ M) of endothelial-intact aorta rings from sham normotensive (circles) and DOCA-salt hypertensive rats (squares) in the presence of vehicle (closed symbols) or allopurinol (100 μM) (open symbols). RA, rat aorta. Points represent means ± S.E.M. percentage of contraction induced by 20 μM PGF_2α for the respective N.

Fig. 4.

Uric acid levels in arterial blood of individual sham normotensive (closed symbols) and DOCA-salt hypertensive (open symbols) rats. Line represents average uric acid for the respective N.

Fig. 5.

A, uric acid-producing activity of XO in sham normotensive (closed bars) and DOCA-salt hypertensive (open bars) aorta. B, H₂O₂-producing activity of XO in sham normotensive (closed bars) and DOCA-salt hypertensive (open bars) aorta. RA, rat aorta. Bars represent means ± S.E.M. for the respective N.

Fig. 6.

A, XO (top) and control α-actin (bottom) protein expression in aorta from sham normotensive and DOCA-salt hypertensive rats. B, band densitometry quantification of XO as the 130-kDa band corresponding to XO. C, band densitometry quantification of XO as percentage of α-actin expression. RA, rat aorta. Bars represent means ± S.E.M. for the respective N.

Fig. 7.

Uricase (top) and control α-actin (bottom) protein expression in aorta from sham normotensive and DOCA-salt hypertensive rats. Positive control (+) for uricase expression is a rat liver lysate. B, band densitometry quantification of uricase as the 64-kDa band corresponding to the uricase dimer. C, band densitometry quantification of uricase as percentage of α-actin expression. RA, rat aorta atrial. Bars represent means ± S.E.M. for the respective N.