Selective action of hydrocortisone on postmitotic epidermal cells in vivo.

Hydrocortisone administered systemically for 3 weeks has no effect on any phase of epidermal cell proliferation as measured by autoradiographic methods. However, the speed of cell differentiation (maturation) is increased, resulting in a thinning of the living epidermis due to the shorter epidermal cell life. Comparison of the epidermis from two body sites (ear and sole of foot) in mice receiving 2.4 mug per gm body weight per day of hydrocortisone in drinking water for 3 weeks revealed no change in the labeling with [3H]thymidine, the mitotic indices, or the lengths of the cell cycle phases. Quantitation of the epidermal cell compartments showed that thinning of the epidermis with hydrocortisone was due to the loss of an identical number of differentiating epidermal cells per unit surface from both body sites. In both sites there was the same increased rate of maturation of postmitotic cells while the proliferative cell-pool remained unresponsive to the hormone. The alteration of the speed of cell maturation is the principal action of hydrocortisone in epidermis. The results indicate that the epidermal cellular concentration of, and the susceptibility to, the hormone were identical in ear and sole of foot despite the differing speeds of turnover of the two tissues.