The effect of Otosporin and Gentisone HC on the mitotic index and thickness of the tympanic membrane and meatal skin in the guinea pig.

Otosporin and Gentisone HC ear drops were inserted twice daily for 3 weeks into the external auditory meatuses of guinea pigs. An intraperitoneal injection of vincristine (1 mg/kg.) was given to each animal three hours before it was killed. Temporal bones and attached external auditory meatuses were dissected, tissues were fixed in 10 per cent buffered formalin, decalcified in EDTA, and embedded in JB4 plastic for sectioning at 4 micron. The proliferative activity in the epidermis of the bony meatus and in the lateral surface of the tympanic membrane was obtained by deriving the mitotic indices. After both types of ear drops there was a statistically significant reduction in mitotic indices, the values being about half the control values. The proliferative activity in the tympanic membrane was too low to permit statistical analysis, but no differences were apparent between the groups. The thicknesses of the epidermis and dermis of the bony canal, and of the tympanic membrane, were measured using a Kontron MOP-AMO3 analyser. Although the dermis was thinner as a result of the administration of ear drops, both the epidermis of the bony meatus and that of the tympanic membrane were thicker, all these changes being statistically significant.