Reactive oxygen species-induced aortic vasoconstriction and deterioration of functional integrity

Oxygen derived free radicals and other reactive oxygen species (ROS) are in volved in a variety of disease states, which can have cardiac and vascular implications. The present study was performed to investigate the mechanism of ROS-induced vasoconstriction and the influence of ROS on the functional integrity of isolated rat thoracic aorta. ROS were generated by means of electrolysis (30 mA, during 0.5, 1, 2 or 3 m in) of the organ bath fluid. ROS induced a transient (approximately 60 min) vasoconstriction and the maximally induced contraction was dependent on th e duration of electrolysis. Dimethyl sulfoxide (DMSO) diminished the ROS-in duced vasoconstriction almost completely, indicating a major influence of h ydroxyl radicals on contractility. The dual cyclooxygenase/lipoxygenase inh ibitor, meclofenamate, completely prevented the ROS-induced vasoconstrictio n. The phospholipase A(2) (PLA(2)) inhibitor, oleyloxyethyl phosphorylcholi ne, was able to reduce the vasoconstriction elicited by ROS by approximatel y 70%. Conversely, the specific cytoplasmic PLA(2) inhibitor arachidonyl tr ifluoromethylketone proved ineffective in this respect. By using the specif ic mitogen-activated protein kinase (MAPkinase) kinase inhibitor PD98059, i t was shown that the activation of extracellular-regulated kinase (ERK) MAP kinase contributes to the ROS-induced vasoconstriction. The effects of ROS on the functional integrity of the aortae were investiga ted, in particular with respect to receptor (alpha(1)-adrenoceptor) and non -receptor-mediated contractile responses (high potassium solution). In addi tion, both the endothelium dependent (methacholine) and endothelium indepen dent (sodium nitroprusside) vasorelaxation were investigated before and aft er ROS exposure. Electrolysis periods of 0.5 and 1 min induced a modest lef tward shift of the concentration response curves for the alpha(1)-adrenocep tor agonist methoxamine. Longer electrolysis periods of 2 and 3 min additio nally decreased the maximal response to alpha(1)-adrenoceptor stimulation. Methacholine-induced vasorelaxation proved diminished in aortae subjected t o electrolysis (0.5, 1, 2 and 3 min), whereas relaxation to sodium nitropru sside was nearly complete in all groups. KCl-induced contractions proved at tenuated only after longer electrolysis periods of 2 and 3 min. This ROS-in duced deterioration of functional integrity was almost completely prevented by 0.6% DMSO. From these results we may conclude that ROS induce an eicosanoid and ERK MA Pkinase-mediated vasoconstriction in isolated rat thoracic aorta. In additi on, exposure to ROS leads to a deterioration of functional integrity charac terized by endothelial dysfunction and decreased contractile function.