DNA Synthesis in Irradiated Hair Follicles of the Mouse

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Abstract
Effects of X-irradiation upon DNA (deoxyribonucleic acid) synthesis were studied in growing hair follicles of mice by the method of labeling with tritiated thymidine and high resolution autoradiography. Hair production was induced in resting hair follicles by plucking, and irradiation was applied at a time when the rate of division in the matrix cells was maximum. The doses applied were 200 rads, which does not cause epilation; 800 rads, which leads to temporary epilation; and 3000 rads, which produces permanent epilation in most follicles. After all 3 doses the rate of DNA synthesis drops rapidly, a reduction to about l/2 occurring in a time (1/2 hr.) short compared with the length of the DNA doubling period (1/4 day). This effect, therefore, must be upon cells in the process of DNA synthesis. DNA production is resumed within 12 hours after irradiation even with the highest dose used, in which case there is almost no resumption of mitotic activity.