Hair growth in skin grafts placed on hairless mice

Abstract The purpose of this study is to investigate the possibility that hair growth is triggered by the loss of a specific hair follicle inhibitor. If the loss of an inhibitor is a sufficient cue for the triggering of hair growth, then hair follicles in skin grafts placed on hairless mice should remain in the growth phase of the hair growth cycle, and never enter the resting phase. This would be expected because hairless skin has no hair follicles, and therefore presumably produces no hair follicle inhibitor itself. Thus, no build‐up of a hair follicle inhibitor within the graft should occur. Female hairless mice (HRS/J) approximately 60 days of age received skin grafts from haired female litteremates. These skin grafts took well and remained healthy throughout the period of investigation, which ranged from 240–380 days. The hair follicles of the grafts undergo cycles of growth and rest. They may remain in the resting phase for as long as two to three months. Therefore, hair follicles of grafts placed on the backs of the hairless mice do not remain permanently in the growth phase of the hair cycle. Additional experiments help rule out the possibility that (1) the lack of continuous hair growth of the hair follicles in the grafts is due to the scar preventing the diffusion of inhibitors from the graft into the host skin, and (2) that the hair follicle remnants in the host hairless skin produce a hair follicle inhibitor in sufficient concentration so that the hair follicles of the graft enter the resting phase.