Free radical-mediated endothelial damage in blood vessels after electrical stimulation

The endothelium plays an important role in mediating vasodilator effects of several agents (acetylcholine, thrombin, A23187, etc.). The goal of this study was to determine the ability of oxygen free radicals generated by electrical field stimulation to alter endothelial function in isolated tissue systems. Tail artery strips and the mesenteric microvasculature isolated from Sprague-Dawley rats were used. Following smooth muscle contraction induced by norepinephrine, these preparations relaxed in response to acetylcholine chloride or ionophore A23187. All vessels were then subjected to electrical stimulation (9 V, 1-2 ms, 4 Hz) of the physiological buffer in which they were bathed or perfused. In some of these preparations, an antioxidant, (10(-4) M sodium ascorbate, 3.6 X 10(-5) M glutathione, 1.3 X 10(-2) M dimethyl sulfoxide) was included in the buffer. Relaxation responses persisted in vessels where an antioxidant had been included in the electrically stimulated buffer. Tissues stimulated without this protection did not relax on subsequent exposures to endothelium-dependent vasodilators. Scanning-electron microscopy of the tissues revealed significant endothelial damage (cell membrane pitting) in tissues exposed to electrical stimulation without antioxidant protection. These results suggest that electrical stimulation causes endothelial damage in isolated vascular preparations. This seemingly adverse effect proves to be a useful tool for removing the endothelium in studies of isolated vascular tissues.