ABSTRACT
The molecular basis for vitamin A and retinoid activity in growth and epithelial function is elusive, and there is considerable debate and controversy even over the relative importance of the plethora of biological effects mediated or induced by retinoids. Retinoid supplementation can dramatically alter epidermal morphology, one of the more obvious changes induced being the dose-dependent induction of epidermal hyperplasia. This chapter discusses the in vivo impact of natural and synthetic retinoids on epidermal morphology and differentiation, and describes the mechanisms involved. Because of the tremendous range of potencies found among retinoid analogs, the doses inducing toxicity vary from retinoid to retinoid. The histochemical localization was similar in retinoid-induced hyperplastic epidermis but the band of staining was more marked and broader reflecting the increased thickness of the stratum granulosum. The "rhino" allelic variant of the hairless mouse has characteristic follicle-derived horn-filled utricles present in the epidermis, the morphology and size of which alter in response to retinoids.
