The stumptailed macaque as a model for baldness: effects of minoxidil

Synopsis Topical application of minoxidil in bald scalps of stumptailed macaques successfully induced regrowth of terminal hairs. The rate and degree of hair growth by minoxidil are much greater in the early stage of baldness in adolescent and young adults. Minoxidil also prevented the development of baldness when applied on non-bald scalps of peri-adolescent animals. Morphometric analysis of hair follicles (folliculograms) has brought a new aspect in observing cyclic dynamics and growth (transformation) of hair follicles. Using this analytic method and autoradiographic observation of DNA synthesis of hair follicles, the action of minoxidil appears to be a potent mitotic stimulator of the follicular as well as peri-follicular germinal (or reserve) cells, thus inducing an enlargement of vellus follicles through the process of cyclic growth and maintaining anagen follicles in the growing phases. Most importantly, minoxidil has no influence in epidermal keratinocytes, sebaceous glands and other dermal components. During almost 3 years of consecutive treatment, the animals showed no detectable local or systemic side effects when examined by laboratory tests of blood cells, chemistry, steroid hormones, measurement of blood pressure and EKG test.