Regulation mechanisms of hair growth

The dorsal resting hair of C3H mice at various ages was shaved, thus activating the hair into the anagen stage. New hair growth after shaving was not uniform in the various age groups. Furthermore, an increasing delay in hair regrowth was observed as the mice became older (20, 66, 188, and 312 days). In the biochemical analysis of hair regrowing and nongrowing skins after shaving, activities of ornithine decarboxylase, transglutaminase, and alkaline phosphatase had higher values in the extract of the hair regrowing area compared with that in the nongrowing area. In studying the effects of various physical and chemical treatments on hair growth after shaving, repeated shaving was in itself clearly shown to stimulate hair growth. Amongst all of the treatments that were applied, topical application of TPA was most able to accelerate hair regrowth, followed by UV irradiation and retinoic acid treatment. Suppression of hair regrowth was observed in PUVA, DHT, and estradiol; and complete inhibition was seen in the animals treated with betamethasone valerate. In biochemical studies, a relatively good correlation was observed between the rate of hair regrowth and skin ODC activities after treatment.