Cyclooxygenase-dependent vasoconstrictor alters vascular function in the vitamin E-deprived rat.

Abstract

We tested the hypothesis that increased production of lipid peroxides, mediated by a dietary vitamin E deprivation, would alter the cyclooxygenase pathway of arachidonate metabolism, resulting in impaired endothelium-dependent vascular function. Mesenteric arteries from control (n = 12) and vitamin E-deprived (n = 12) Sprague-Dawley rats were studied in a myograph. Endothelium-dependent relaxations to methacholine were similar in the arteries from vitamin E-deprived rats compared with control arteries (EC50, 0.057 +/- 0.006 versus 0.065 +/- 0.009 microM). However, in the arteries from the vitamin E-deprived rats, this response was potentiated in the presence of a cyclooxygenase inhibitor (1 microM meclofenamate; EC50, 0.035 +/- 0.003 versus 0.057 +/- 0.006 microM; P < .05) or thromboxane A2/prostaglandin H2 receptor blocker (1 microM SQ 29548; EC50 0.029 +/- 0.002 versus 0.057 +/- 0.006 microM; P < .05) but had no effect on the arteries from the control rats. Endothelium-independent relaxations to sodium nitroprusside were not effected by vitamin E deprivation. Arachidonic acid increased tension twofold more in the arteries from the vitamin E-deprived rats compared with the control rats (at 1 microM; 0.43 +/- 0.05 versus 0.23 +/- 0.03 mN/mm; P < .05). The enhanced vasoconstriction was blunted, and the group difference was eliminated by a cyclooxygenase inhibitor (0.15 +/- 0.02 versus 0.43 +/- 0.05 mN/mm, P < .05) or a thromboxane A2/prostaglandin H2 receptor blocker (0.17 +/- 0.04 versus 0.43 +/- 0.05 mN/mm, P < .05). Prostaglandin endoperoxide synthase expression, determined by Western immunoblotting on aortas from the same rats, was increased in the vitamin E-deprived rats (3.14 +/- 0.8 versus 1.06 +/- 0.4 fmol/ng DNA, P < .05). In summary, mesenteric arteries from the vitamin E-deprived rats demonstrated altered endothelium-dependent responses that were in part due to a cyclooxygenase-dependent vasoconstrictor binding to the thromboxane A2/prostaglandin H2 receptor. In the aorta, there was an associative increase in the expression of prostaglandin endoperoxide synthase. We speculate that, in some vascular diseases, increased lipid peroxidation may influence endothelium-dependent vascular function by modulating the cyclooxygenase pathway of arachidonate metabolism.