EFFECTS OF ALPHA-ISOPROTERENOL ON DENERVATION ATROPHY IN ORBICULARIS OCULI MUSCLE-FIBERS

The effect of the beta-adrenoceptor agonist isoproterenol on the dener vated orbicularis oculi muscle was studied. We cut the facial nerve on the right side of eight rats and injected isoproterenol (5 mg/kg) int o four rats every day. The animals were sacrificed after three weeks, and small pieces of the orbicularis oculi muscle were removed. Muscle fibers were separated into single fibers. Cytochrome oxidase enzyme st aining was applied, and density of cytochrome oxidase enzyme product a nd diameter of individual muscle fibers were analyzed by computer. Som e of the muscle fibers were observed under electron microscopy. The re sults showed that diameter and cytochrome oxidase enzyme activity of t he orbicularis oculi muscle decreased by denervation, otherwise, it in creased to near the normal level by administration of isoproterenol. E lectron microscopic observation showed that the myosion filaments beca me thin and their arrangement were disordered by denervation and their findings recovered to be almost normal by isoproterenol administratio n. We concluded that isoproterenol could prevent the orbicularis oculi muscle from atrophying which caused by denervation.