Hair growth and its relation to vascular supply in rotated skin grafts and transposed flaps in the albino rat.

HAIR-GROWTH in the rat occurs in a series of waves which start ventrally and pass over the flanks to the back (Dry, 1926; Butcher, 1934). In our colony of randomly mated albino rats the first wave begins at about 5 weeks of age and is complete 3 weeks later; the second wave starts at 8|-9 weeks of age and is not complete until a further 12-14 weeks have elapsed. In both these waves dorsal hairs are longer than ventral ones, and this appears to be due to a longer growing period rather than to any differences in the rate of growth (Johnson, 1958a). Haddow & Rudall (1945) demonstrated that such waves of growth are accompanied by increased vascularization of the dermis, and suggested that follicles become active as a response to increased vascularity. Durward & Rudall (1949) seem to have modified this view to the extent of suggesting that vascularization cannot cause follicular activity until a required resting stage has been completed. Our experiments involved the transplantation or transposition of hair follicles, i.e. removing them from their original blood-supply and allowing them to develop vascular connexions in their new sites. First, we wanted to discover whether the activity of the hair follicle is consequent upon, or in fact initiates, vascularization. Secondly, we wanted to know whether short ventral and longer dorsal hairs are characteristic of their respective follicles, or whether the hairlength merely depends on the site of the follicle. Previous investigators have reached differing conclusions. Butcher (1936) believed that transplanted follicles behave according to their new position (i.e. site wise), although his pioneer work is not easy to interpret because the experiments were not designed in the light of a detailed knowledge of the hair-growth cycles. Durward & Rudall (1949), who twisted lateral strips of skin in rats leaving the blood-supply as intact as possible, and Ghadially (1957) who, in the rabbit, devised an ingenious transposition of skin flaps with their original connexions