The permeability of hyperplastic oral epithelium.

An epithelial hyperplasia is one of the reactions of skin and oral mucosa to chemical and mechanical insult. It is usually assumed that this reaction produces a more effective epithelial barrier, but there is no information as to whether a less permeable tissue results. To examine this question, hyperplasia was induced in the cheek pouches of hamsters by either chemical treatment with 0.0025% TPA in acetone or by mechanical abrasion with a rotating mop; untreated hamsters served as controls. The animals were killed and the cheek pouches were removed, mounted in diffusion chambers and the permeability to labelled water and horseradish peroxidase (HRPO) determined. The results showed that higher values were obtained for the permeability constant of hyperplastic epithelia than for that of control tissue, suggesting that an increased epithelial thickness is not necessarily associated with an improved permeability barrier function. The presence of an inferior barrier layer in hyperplastic epithelia may be related to the increased rate of turnover of this tissue.