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

In vivo and in vitro experiments were conducted to investigate the effect of 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 physiological saline in 4 rats, for 21 consecutive days. After the 3-week treatment, bilateral cochleas were excised for frozen sections and stained for cytochrome oxidase. The staining density of the stria vascularis for the enzyme was analyzed with a computer. Electron microscopic observation was also performed for some specimens. As for the in vitro experiments, bilateral cochleas from 6 normal rats were excised for cell culture. Cochlear cells from the right ear were cultured with medium containing alpha-isoproterenol (10-micromol/L concentration), and those from the left ear with medium alone. After 3-day culture, the enzyme activity of cytochrome oxidase in the stria vascularis was quantified by the same method used for the in vivo experiments. Cytochrome oxidase activity was markedly elevated in the alpha-isoproterenol group. The activity tended to be higher in the lower turns of the cochlea. Electron microscopy revealed that numerous mitochondria were present in marginal cells that protruded into the endolymphatic space. The enzyme activity 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 probably 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.