Effects of prostacyclin on hearing recovery after repetitive noise and on histomorphology of the inner ear in the guinea pig.

A probable relation between prostaglandin formation and the pathophysiology of hearing loss led to the application of the potent vasodilator prostacyclin in the treatment of inner ear disorders. Two drugs may be administered to humans: (1) unstable natural prostacyclin (epoprostenol) with a strong biological potency but with a high first-pass effect, or (2) a prostacyclin analogue (taprostene) with less biological activity, but a longer biological half-life and intravenous application. Therefore, the purpose of this study was to investigate potential differences of both drugs in their effect on the inner ear. The therapeutic potency of both drugs was evaluated in a recently developed animal model consisting in the recovery of hearing after a temporary threshold shift obtained by two noise exposures at 100 dB. In addition, the ultrastructure of the stria vascularis was examined by electron microscopy after the application of the drugs. After administering epoprostenol (12 ng/kg body weight/min) and taprostene (25 ng/kg body weight/min) histomorphological alterations in the stria vascularis did not differ from the controls. In the repetitive low-level noise model, neither drug showed a significant difference in its effect on the recovery of the hearing threshold. The results indicate that in the guinea pig epoprostenol has the same effect on the hearing threshold as the stable analogue taprostene, as shown by auditory brain stem response.