A sensitive culture system was used to investigate whether in vitro senescence is associated with loss of responsiveness to relevant growth factors in the cellular environment. Early passage dermal fibroblasts obtained from healthy newborns and adults were maintained 4 to 6 days in medium containing either fetal calf serum or five defined growth factors. Newborn fibroblasts consistently grew far better than adult fibroblasts in both media; dose-response curves demonstrated a greater response by newborn fibroblasts to both serum mitogens and to thrombin, insulin, and epidermal growth factor alone and in combination. These data suggest that newborn fibroblasts generally have greater mitogenic responsiveness than adult fibroblasts and that age-associated loss of growth factor responsiveness may indeed contribute to the decreased proliferative capacity of old cells.

Synopsis Clinically recognized age-associated changes in skin are considerably more prominent in chronically sun-exposed areas and in fair-skinned individuals relatively lacking a MELANIN barrier. PREMATURE AGING due to sun exposure is now widely accepted by dermatologists as well as the lay public, but has proven difficult to quantitate and therefore to study. In the laboratory, it has been possible to demonstrate behavioral differences in cells cultured from both the epidermis and dermis that are almost certainly due to prior sun exposure. Paired skin biopses from the habitually sun-exposed and nonexposed aspects of the

Examination of the skin or hair with Wood's lamp has long been used to aid in the clinical diagnosis of some cutaneous disorders. A new observation reported here illustrates that Wood's light can be used to determine the depth of melanin pigmentation in the skin: contrast in epidermal pigmentation is increased while contrast in dermal pigmentation is decreased under Wood's lamp illumination compared to ambient visible light. The principles underlying this phenomenon are discussed. Use of the Wood's lamp to localize abnormal melanin pigmentation in the skin can be a guide to clinical diagnosis of hypermelanosis.