Activated oxygen molecules generated by electrical stimulation affect vascular smooth muscle.

Although electrical field stimulation has been used to evoke neural responses in blood vessels this technique can also generate activated oxygen molecules which may affect the experimental preparation. We evaluated this by stimulating 10 cc of aerated Krebs-Henseleit solution for a period of 20 s and then transferring the fluid to a pre-contracted segment of bovine pulmonary artery. The parameters required to achieve 50% maximal relaxation were a voltage of 4.0 +/- 0.3 volts (mean +/- S.E.), a frequency of 1.6 +/- 0.1 Hz and a pulse duration of 0.37 +/- 0.02 ms. Exposure to stimulated fluid caused greater amounts of relaxation in vessels pre-contracted with serotonin than in those pre-contracted with either histamine or potassium chloride. Relaxation was not endothelial dependent and it was not inhibited by adrenergic or cholinergic blockade. Since both ascorbate and catalase but not superoxide dismutase inhibited relaxation, it appears that hydrogen peroxide is involved. We conclude that even low intensity electrical field stimulation generates activated oxygen molecules in oxygenated physiologic buffer solution and that these molecules can relax blood vessels both directly and by altering the response to drugs in the muscle bath. These effects must be considered when using electrical field stimulation to study blood vessels.