QUANTITATIVE STUDIES OF HAIR GROWTH IN THE ALBINO RAT

Abstract

SUMMARY: 1. Spaying of female rats aged 7 weeks accelerated the passage of the second wave of hair growth. Longer hairs were produced as a result of faster growth, and the rate of loss of dead or 'club' hairs [cf. Johnson, 1958] was increased. 2. Oestradiol implanted into spayed females delayed the initiation and passage of the wave. Shorter hairs were produced by a reduced rate of growth, and loss of club hairs was inhibited. 3. Castration of male rats aged 7 weeks accelerated the passage of the second wave of growth, and implantation of testosterone slowed it down. Testosterone had no effect on the definitive length of hair produced or on the rate at which club hairs were lost. 4. Oestradiol implanted into castrated males produced the same effects as in spayed females except that it had no effect on the time of initiation of the wave. 5. Combined implantation of testosterone with oestradiol into castrated males did not off-set the inhibitory effects of the oestradiol on hair length or rate of loss of club hairs, but may have slightly speeded the hair wave.