Human Hair Follicles: Metabolism and Control Mechanisms*

Abstract

TESTOSTERONE metabolism, and the ADENYL CYCLASE system of human hair follicles suggest the following mechanisms of transformation of the hair follicles from the terminal to the veilus type: Testosterone carried in plasma reaches the hair follicles, where it is converted to 5a-dihydrotestosteronc, a tissue-active androgen. Since the hair follicles have sufficient 5a-reductase to catalyze this conversion, the intracellular level of TPNH is presumed to be the rate-limiting factor at this step. The growing hair follicles appear to generate sufficient TPNH via the penrose cycle. Probably 5a-dihydrotestosterone but not testosterone is the tissue-active androgen, since adenyl cyclase in the hair follicles is markedly inhibited by 5a-dihydrotestosterone but not by testosterone. Inhibition of adenyl cyclase decreases the intracellular level of cyclic AMP. This decrease of cyclic AMP, in turn, will create premature completion of the anagen state. Years of repetition of this premature completion probably produces the short veilus-type hairs and hair follicles. Although solid proof for the entire process of BALDNESS is not yet available, the initial roles played by 5a-dihydrotestosterone and adenyl cyclase are highly significant in these complex mechanisms.