MAST-CELL INVOLVEMENT IN MURINE HAIR-GROWTH

We have examined the possibility that an involvement in hair growth re gulation is one of the still obscure physiological roles of mast cells (MC) in normal skin. Using the murine hair cycle as a model, we first studied the number, localization, and granulation status of skin MC d uring the hair cycle of C 57 BL-6 mice. Shortly after the induction of hair growth (anagen) in the back skin of mice with resting (telogen) follicles, a sharp decline in the number of Giemsa-stainable MC was de tected by morphometry. This was evident in depilation-induced, pharmac ologically induced, and spontaneous anagen. By light and electron micr oscopy, the anagen-associated decline was correlated with the occurren ce of substantial MC degranulation. In vivo the IgE-independent MC sec retagogues, compound 48/80 and ACTH, induced anagen in mouse telogen f ollicles after intracutaneous administration, while inhibitors of mast cell degranulation (cromoglycate, tiacrilast) and antagonists of sele cted MC products (clemastin, ranitidin, ketanserin) significantly reta rded the induced development of anagen follicles in these mice. It is suggested that MC act via their secretory products as stimulators of a nagen development in mice and that the murine hair cycle is an excelle nt model for studying growth regulatory functions of MC in development ally regulated systems. (C) 1994 Academic Press, Inc.