Hair Growth and its Relation to Vascular Supply in Rotated Skin Grafts and Transposed Flaps in the Albino Rat

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Abstract
Hair follicles of albino rats were translocated and allowed to develop vascular connexions in new sites. The translocation was achieved either by rotation of skin grafts in the mid-flank before the expected start of the first wave of growth (4 weeks after birth), or by transposition of flaps—in two stages—so that they were never completely cut off from a blood-supply. The first and second waves of hair-growth on the body adjacent to the grafts or flaps continued as in intact rats; the waves of growth moved from ventral to dorsal, and the dorsal hairs were longer than ventral ones. The appearance of hair of the first wave on unrotated control grafts was in retard of that on the body, but passed from ventral to dorsal in the normal way. During the second wave of growth, follicular activity on the graft continued out of phase with that on the body. The first and second waves of hair-growth on rotated grafts were similarly retarded, but began in the dorsal region and passed ventrally. There was no retardation of growth on the transposed flaps. Hairs first appeared on the dorsally transposed ventral skin of the flaps at the same time as on the ventral body, followed by growth on the ventral flap and dorsal body. The length of hair produced on both rotated grafts and transposed flaps was consistent with the origin of the follicles and not in accordance with their new positions. In intact rats it was demonstrated that follicular activity precedes vascularization. Vascularization of follicles in grafts or transposed flaps was always consequent upon follicular activity, even when this was out of phase with the normal waves of hair-growth on the adjacent body. The evidence suggests that follicular activity depends mainly on an inherent rhythm, and that the hyperaemia which accompanies hair-growth is consequent upon an innate demand of the follicles and is not itself the cause of their activity.