Systemic influence on activity of hair follicles in skin homografts.

ACTIVITY of the hair follicle is cyclic, periods of hair-growth alternating with periods of quiescence during which the dead hair is retained as a 'club'. In the rat, hair-growth occurs in a series of waves which start ventrally and pass over the flanks to the back (Dry, 1926; Butcher, 1934; Johnson, 1958a). The object of our work was to find out how far such activity is dependent upon factors within the follicle and how far it is subject to systemic control. When hair follicles are translocated, either by rotation of grafts in the mid-flank or by transposition of flaps in two stages, they continue to maintain the periodicity characteristic of their sites of origin (Ebling & Johnson, 1959). Vascularization of such follicles is always consequent upon follicular activity, even when this is out of phase with the normal waves of hair-growth on the adjacent body. This evidence suggests that follicular activity is inherent and that the hyperaemia which accompanies hair-growth is consequent upon an innate demand of follicles and is not itself the cause of their activity. Nevertheless, the fact that, when the resting phase is prolonged by steroid hormones or shortened by gonadectomy or adrenalectomy (Johnson, 1958 b, c), the pattern of the hair-growth waves is never altered suggests that some form of systemic control is involved. The possibility of a systemic influence could be harmonized with the evidence of inherent properties by supposing that a systemic rhythm is superimposed on local differences of reactivity. If, for example, follicular activity in different regions of the body were determined by graded thresholds to a systemic stimulus, then translocated autografts would appear to behave selfwise. On the other hand, normally sited homografts might not do so and it seemed desirable to investigate their behaviour.