• The bulla in guinea pigs was filled with 0.01%, 0.1%, and 0.5% vitamin A acid (retinoic acid) solution once or twice daily for an average of five days. Pure arachnoid oil was used as a control solution. The mucous membrane appeared normal in the ears receiving arachnoid oil or 0.01% vitamin A acid. In bullae receiving 0.1% and 0.5% solutions, the epithelium remained close to normal, but there were small areas of ossification that were particularly notable in the submucosal layer. There was no indication that the normal guinea pig mucosa showed a metaplastic change into a secreting gland, forming epithelium.
(Arch Otolaryngol 1981;107:230-232)
Palva T, Ylikoski J, Savolainen S, Mäkinen J. The Effect of Vitamin A Acid on the Middle Ear of the Guinea Pig. Arch Otolaryngol. 1981;107(4):230–232. doi:10.1001/archotol.1981.00790400032007