Retinoid stimulation of epidermal differentiation in vivo.

Retinoids are potent inducers of epidermal hyperplasia in vivo. Epidermal transglutaminase activity and stratum corneum turnover were examined in all-trans-retinoic acid and arotinoid ethyl ester treated hairless mice, to evaluate the possible contribution of decreased epidermal cell loss to the induction of hyperplasia by retinoids. Stratum corneum turnover was enhanced, and the absolute amounts (activity/cm2), but not the specific activities, of soluble and particulate transglutaminase increased following retinoid treatment. Since epidermal differentiation was enhanced after retinoid treatment, the hyperplastic response is due to increased cell formation and not decreased cell loss.