Abstract
When tarsometatarsal skin of 13-day-old chick embryos that had been cultured in medium containing 5% delipidized FCS with or without retinol (20μM) and/or hydrocortisone (20nM) for 1 day was cultured in a chemically defined medium without either the hormone or retinol for 1 day, epidermal DNA synthesis of hydrocortisone-and/or retinol-pretreated skin was inhibited when compared to that of control skin. The addition of epidermal growth factor (EGF, 10ng/ml) to retinol- or hydrocortisonepretreated skin further inhibited the epidermal DNA synthesis. Epidermal DNA synthesis in retinoland hydrocortisone-pretreated skin was more strongly inhibited than in retinol-or hydrocortisonepretreated skin, but was not further inhibited by EGF. In epidermis which was induced to differentiation toward keratinization by hydrocortisone or mucous metaplasia by retinol, EGF inhibited DNA synthesis. The extent of [125I]-EGF binding to the epidermis of retinol- and hydrocortisone-pretreated skin was 160-180% that in control skin, with no change in affinity. Hence there is no correlation between EGF-binding and the mitogenic activity of EGF.
