all-trans-Retinoic acid at concentrations greater than 10(-7)m stimulated the incorporation of d-[(3)H]glucosamine into 8m-urea/5% (w/v) sodium dodecyl sulphate extracts of 1m-CaCl(2)-separated epidermis from pig ear skin slices cultured for 18h. The incorporation of (35)SO(4) (2-), l-[(14)C]fucose and U-(14)C-labelled l-amino acids was not significantly affected. 2. Electrophoresis of the solubilized epidermis showed increased incorporation of d-[(3)H]glucosamine into a high-molecular-weight glycosaminoglycan-containing peak when skin slices were cultured in the presence of 10(-5)m-all-trans-retinoic acid. The labelling of other epidermal components with d-[(3)H]glucosamine, (35)SO(4) (2-), l-[(14)C]fucose and U-(14)C-labelled l-amino acids was not significantly affected by 10(-5)m-all-trans-retinoic acid. 3. Trypsinization dispersed the epidermal cells and released 75-85% of the total d-[(3)H]glucosamine-labelled material in the glycosaminoglycan peak. Thus most of this material was extracellular in both control and 10(-5)m-all-trans-retinoic acid-treated epidermis. 4. Increased labelling of extracellular epidermal glycosaminoglycans was also observed when human skin slices were treated with all-trans-retinoic acid, indicating a similar mechanism in both tissues. Increased labelling was also found when the epidermis was cultured in the absence of the dermis, suggesting a direct effect of all-trans-retinoic acid on the epidermis. 5. Increased incorporation of d-[(3)H]-glucosamine into extracellular epidermal glycosaminoglycans in 10(-5)m-all-trans-retinoic acid-treated skin slices was apparent after 4-8h in culture and continued up to 48h. all-trans-Retinoic acid (10(-5)m) did not affect the rate of degradation of this material in cultures ;chased' with 5mm-unlabelled glucosamine after 4 or 18h. 6. Cellulose acetate electrophoresis at pH7.2 revealed that hyaluronic acid was the major labelled glycosaminoglycan (80-90%) in both control and 10(-5)m-all-trans-retinoic acid-treated epidermis. 7. The labelling of epidermal plasma membranes isolated from d-[(3)H]glucosamine-labelled skin slices by sucrose density gradient centrifugation was similar in control and 10(-5)m-all-trans-retinoic acid-treated tissue. 8. The results indicate that increased synthesis of mainly extracellular glycosaminoglycans (largely hyaluronic acid) may be the first response of the epidermis to excess all-trans-retinoic acid.
