Quantitative Models for the Study of Hair Growth in Vivo^a

In 1991, researchers developed a quantitative method to study hair growth in vivo, focusing on the histogenesis of baldness in stumptailed macaques and using a morphometric method to create "folliculograms." They discovered that alopecia in macaques was due to smaller hair follicles, not fewer in number, and was linked to puberty and increased androgen levels. The condition could be prevented with antiandrogens. The study also found that 5% minoxidil was more effective than 2% in promoting hair regrowth and follicle size. A study with six macaques treated with an antiandrogen showed decreased 5α-reductase activity, unchanged serum androgens, and increased hair weight, preventing frontal baldness. Additionally, minoxidil treatment in fuzzy rats, a genetic model for hair growth, increased the size of anagen follicles and stimulated growth in dormant vellus telogen follicles. The document concludes that vellus follicles have the potential for regrowth, but continuous androgen effects can cause regression unless blocked locally. The macaque and rat models were deemed relevant for studying human androgenetic alopecia and for drug screening.