DNA ploidy changes in rhino mouse skin induced by all-trans retinoic acid and retinol

Objective: In order to assess the proliferative changes induced by all-trans retinoic acid (RA) and retinol (ROL), we have carried out a study of the DNA content of basal and suprabasal keratinocytes after epicutaneous application on the rhino mouse. Study Design: Skin sections were analyzed ste-reologically and cytophotometrically using the Feulgen technique. The diploid DNA value (2C) was obtained from hepa-tocyte nuclei of control animals. Whereas cells inphase G₀-G₁ will show a 2C content, cells during phase S and in phase G₂-M will show DNA values ranging from 2C to 4C and 4C, respectively. Results: Although epidermal thickness (ET) increased significantly in all treated animals, surface density only increased in animals treated with all-trans RA. Quantification of DNAcontent of basal keratinocytes showed reduction of 2C and 2C-4C populations with a commensurate increase in proportions of cells with 4C and > 4C in the animals treated with 0.025% all-trans RA and ROL. Suprabasal keratinocytes of mice treated with 0.025% all-trans showed a decrease of the 2C population and an increased proportion of cells with 4C. Whereas 0.025% all-trans RA induced an increase of both basal and suprabasal DNA indices, ROL enhanced only the basal DNAindex significantly. Conclusion: Animals treated with 0.025% ROL showed a significant increase in the basal proliferative index (PI) while the suprabasal PI remained constant; treatment with 0.025% all-trans RA produced a significant increase of both basal and suprabasal PIs and parakeratotic hyperkeratosis probably due to incomplete differentiation.