QUANTITATIVE STUDIES OF HAIR GROWTH IN THE ALBINO RAT

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Abstract
SUMMARY: 1. Adrenalectomy 2 weeks before the start of the second wave of hair growth advanced the beginning of the wave in female rats, and speeded its passage over the body in both males and females. The rate of loss of club hairs was slightly accelerated, but there was no effect on the definitive length of hair produced. 2. Adrenalectomy after the wave of hair growth had begun was less effective. 3. ACTH did not affect the time at which the wave of hair growth began but delayed its passage. ACTH had no effect on the loss of club hairs nor on the definitive length of hair produced. 4. Implantation of oestradiol retarded the start and rate of passage of the wave, and the loss of club hairs in both spayed and spayed adrenalectomized animals. Oestradiol must therefore have some action which is independent of the adrenals. Nevertheless, inhibitory effects of oestradiol on these aspects of hair growth were enhanced by the presence of the adrenals. The action of oestradiol in reducing the rate of hair growth was, on the other hand, unaffected by the presence or absence of the adrenals. 5. Adrenal hormones delay the passage of the growth wave to a greater extent than ovarian hormones, but they have no effect on the rate of hair growth, and, compared with ovarian hormones, affect the loss of club hairs only slightly. It is therefore suggested that these three main phases of hair growth may be controlled by mechanisms which are at least partially independent.

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