Pigment Clumping in Growing Hair Follicles of Mice a Sensitive Radiobiological Model

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Abstract
Alteration in the structure or function of hair follicles have been recognized as reliable indicators of damage induced by radiation or chemicals. The damage has been expressed as epilation, changes in hair colour and follicular dysplasia. This paper introduces a new method for analysing damage in hair follicles. The criterion of damage involves the production of densely-pigmented cells in an abnormal location: the mitotically-active matrix region of the growing hair follicle. This hyperpigmentation is a sensitive indicator, produced by relatively low doses of radiation or chemicals. As used here, the change is quantal, follicles being recognized as normal-appearing or affected on the third day after treatment. The fraction of normal follicles decreases exponentially with increasing dose of three treatment modalities: x-rays to the skin surface, ultra-violet radiation to the skin undersurface, or actinomycin-D injected subcutaneously. Expressed in contemporary radiobiological terms, the dose—response curves extrapolate to a number between 1·5 and 2·1 and they have D0 values of 55 rads of x-rays, 105 mJ/cm2 of U.V.R., or 42·5 µg of actinomycin-D/kg body-weight. The D50 doses are 70 rads, 105 mJ/cm,2, and 43 µg/kg, respectively.