Effect of a beta-stimulant on the inner ear stria vascularis

In vivo and in vitro experiments were conducted to investigate the effect o f alpha-isoproterenol on the inner ear stria vascularis with intracellular cytochrome oxidase activity used as an index. Intraperitoneal injection of alpha-isoproterenol (5 mg/kg) was performed in 10 rats, and that of physiol ogical saline in 4 rats, for 21 consecutive days. After the 3-week treatmen t, bilateral cochleas were excised for frozen sections and stained for cyto chrome oxidase. The staining density of the stria vascularis for the enzyme was analyzed with a computer. Electron microscopic observation was also pe rformed for some specimens. As for the in vitro experiments, bilateral coch leas from 6 normal rats were excised for cell culture. Cochlear cells from the right ear were cultured with medium containing alpha-isoproterenol (10- mu mol/L concentration), and those from the left ear with medium alone. Aft er 3-day culture, the enzyme activity of cytochrome oxidase in the stria va scularis was quantified by the same method used for the in vivo experiments . Cytochrome oxidase activity was markedly elevated in the alpha-isoprotere nol group. The activity tended to be higher in the lower turns of the cochl ea. Electron microscopy revealed that numerous mitochondria were present in marginal cells that protruded into the endolymphatic space. The enzyme act ivity was also elevated in the stria vascularis from cochlear specimens in the alpha-isoproterenol group of the in vitro experiment. The above results suggest that alpha-isoproterenol accelerated the metabolic activity of the cells that constitute the stria vascularis. The increase in activity was p robably attributable to direct pharmaceutical effects of the beta-stimulant , rather than an increase in blood flow. It is possible that the cells that constitute the stria vascularis may have beta-receptors.