Mechanical stimulation of dorsal mouse skin by skin massage or removal of the horny layer results in a mutually comparable increase in DNA-labelling and mitotic activity. However, only after injury such as removal of the horny layer hyperplasia develops. This phenomenon, called 'hyperplastic transformation' is characterized by a transient abolition of the epidermal GI chalone responsiveness. There is some indication that the susceptibility to a heat labile factor, probably the epidermal G2 chalone, is not affected. Skin massage neither interferes with the responsiveness to epidermal G1 chalone nor induces 'hyperplastic transformation'.Mouse tail epidermis shows a 'functional hyperplasia' and responds to the GI chalone. To explain these observations, it is assumed that the epidermal stem cell population is heterogeneous consisting of GI chalone-sensitive and G1 chalone-insensitive cells.

Using capillary endothelial cells from the coronary system of guinea pig heart, we have devised an in vitro assay suitable for measuring proliferative and growth-promoting effects mediated by drugs and growth factors. In this assay, hemodialysate and fractions isolated from it--consisting exclusively of low-molecular-weight compounds from calf blood--stimulate the proliferation of coronary endothelial cells. This effect is not a trivial nutritive one. Furthermore, in respect to the stimulation of proliferation, hemodialysate synergizes with epidermal growth factor, basic fibroblast growth factor, and endothelial cell growth factor, but not with insulin, which shows no proliferative effect in our system. From data obtained by analysis of hemodialysate fractions, it is deduced that the active compounds are strongly negatively charged oligosaccharides with a molecular weight of apparently 3000 Dalton. The synergistic effect of hemodialysate compounds on proliferation of endothelial cells as well as their previously demonstrated insulin-like activity is believed to explain the therapeutic efficacy of hemodialysate in cases of impaired wound healing and occlusive diseases.

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Abstract. A cut made into the back skin of either newborn or adult mice evokes, at both ages, a hyperproliferative response in the epidermis. Differences in the reaction of neonatal as compared with adult epidermis are found in the spatial distribution of proliferative activity as well as in its time course. The response in adult mouse epidermis is inhibited by local application of indomethacin, whereas the response of the newborn epidermis is not.