Hair Loss Blog

J Exp Med. 1924;40:517

THE PRODUCTION OF PERSISTENT HAIR LOSS IN RABBITS BY ROENTGEN RADIATION;
Clark H, Sturm E.

Seven areas on the abdomen of each of fourteen rabbits were exposed to soft Roentgen radiation of constant quality in doses varying, in the region of the value critical for the production of persistent hair loss (which did not regrow), by regular steps of about 4 per cent. Without exception the critical dose was found to lie between two such values, the upper limit being represented by exposures on eight of the animals and the lower on ten of them. With certain reservations, the critical dose corresponds to the production of 2.04 x 10(15) ions of either sign per gm. of tissue.

Edited for hair loss blog

J Invest Dermatol. 1976;67:98-105.

Hair.
Ebling FJ.

The psychologic importance of hair to man is in inverse ratio to its physical function. Except for scalp hair and desultory areas of sexual hair, most of man's hair follicles are vestigial. Three problems of hair regrowth remain to be solved: (1) how the intermittent activity of hair follicles in both animals and man is controlled; (2) how the male hormone alters the hair cycle in human skin; and (3) why larger hairs are produced by testosterone in some areas of the body when in some individuals the hair follicles in the scalp regress. Studies in which skin grafts from rats of different ages were exchanged showed that hair follicles are innately programmed but can be slowly influenced by systemic factors. Steroid hormones, especially estrogens, slow down the moult cycle whereas thyroid hormones accelerate it. What establishes the innate rhythm remains problematical. The fact that plucking out the club hair initiates activity in resting follicles has been explained by the hypothesis that the mitotic inhibitor which accumulates during anagen is normally used up or dispersed during telogen or by wounding. However, contrary to this theory, follicular activity is not prolonged by epilation during anagen. Moreover, if rats are epilated within one or two days of eruption, only club hairs are removed since forceps cannot grasp the tips of the new hairs. Such epilation does not affect the anagen in progress, but remarkedly enough the subsequent resting phase is shortened. Both sexual hair and male-pattern baldness depend on androgenic hormones. Target organs of testosterone convert the hormone to active metabolites, chiefly 5alpha-dihydrotestosterone. In skin, however, 5alpha-dihydrotestosterone may not be the only active tissue androgen. The major metabolite of testosterone incubated with hair roots in androstenedione, and hirsute women without other obvious endocrine abnormality sometimes excrete high levels of androstanediol. Both steroids stimulated the sebaceous glands of hypophysectomized-castrated rats, which, however, showed only a limited response to testosterone. The androgenic steroids, the enzymes that convert them to their active metabolites, and the proteins that bind them are undoubtedly very important to the problems of the growth of sexual hair and male-pattern baldness.

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Praxis (Bern 1994). 1997 Jun 4;86(23):979-81

Cycle of hair growth and evaluation of alopecia

Piérard-Franchimont C, Piérard GE.

Hair follows a cycle of growth and involution which is asynchronous among follicles. Three phases are distinguished, namely the anagen growth phase and the catagen and telogen phases of regression. Any kind of alopecia results from perturbations of the hair cycle. Among triggering factors, various hormones, cytokines and apoptosis-inducing agents are currently recognized. Some microorganisms inducing inflammation could modulate the severity of selected hair loss disorders.

Skin Pharmacol. 1993;6(3):170-8.

Potassium channel openers stimulate DNA synthesis in mouse epidermal keratinocyte and whole hair follicle cultures.

Harmon CS, et al

We have conducted studies using primary mouse epidermal keratinocyte and whole hair follicle cultures to investigate the mechanism of the hypertrichotic ( hair regrowth-inducing ) activity of potassium channel openers. In a time course study, the extent of stimulation of epidermal keratinocyte DNA synthesis by minoxidil increased as the rate of DNA synthesis in control cultures declined. Minoxidil stimulation of DNA synthesis in 7-day cultures required prolonged exposure to the agent. Pinacidil and diazoxide also stimulated DNA synthesis in mouse epidermal keratinocyte cultures. In addition, minoxidil, pinacidil, diazoxide, and cromakalim stimulated DNA synthesis in whole-organ cultures of mouse hair follicles. These results suggest that potassium channel openers retard the loss of proliferative activity of differentiating keratinocytes and support the hypothesis that these agents stimulate hair regrowth through a direct effect on hair follicles.

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