Determination of prednisolone in the cochlear tissue

Although glucocorticoids are widely used to treat inner ear diseases, glucocorticoid concentration has never been determined in the cochlear tissue. The aim of the present study was to measure the prednisolone concentration in the cochlear tissue after intravenous administration. At 0.5, 1, 2, 4 or 8 h after the injection (100 mg/kg), cochlea, hepatic and brain tissue and serum were removed, and prednisolone extracted from these samples was measured using high-performance liquid chromatography. Although prednisolone was not detected in the brain tissue, it was detected in the hepatic tissue and serum, demonstrating the peak value at 30 min after administration and a rather rapid decline with time thereafter. Prednisolone was also detected in the cochlear tissue, but the uptake and elimination patterns were entirely different from other samples. The prednisolone level in the cochlea reached the peak value 1 h after administration and gradually declined. The present study shows that the prednisolone administered is gradually transported to the cochlear tissue from blood and remains at higher concentrations than in the hepatic tissue or serum over several hours. It is highly likely that this slow elimination is closely related to the therapeutic effect of steroids in inner ear diseases.