Effects of isoproterenol on the orbicularis oculi and stapedius muscles

The effect of the beta-adrenoceptor agonist, isoproterenol, on the orbicularis oculi and stapedius muscles was studied. Rats were injected with isoproterenol (5 mg/kg) every day. The animals were sacrificed after 1 and 2 weeks, and the orbicularis oculi muscle and stapedius muscle were removed. Muscle fibers were separated into single fibers, and cytochrome oxidase enzyme staining was applied with 1% MnCl2, DAB + H2O2. The density of cytochrome oxidase enzyme reaction products and the diameter of individual muscle fibers were analyzed by computer-assisted measurement. The administration of isoproterenol increased the activity of cytochrome oxidase as well as the diameter of muscle fibers in the orbicularis oculi muscle and stapedius muscle. It was suggested that these muscle fibers exhibited increases in functional activity after the administration. The results showed that the diameter and cytochrome oxidase enzyme activity of the orbicularis oculi and stapedius muscles increased. We conclude that isoproterenol induces hypertrophy of the orbicularis oculi and the stapedius muscle fibers, and promotes cytochrome oxidase enzyme activity.