Hair loss from high DHT levels is one of the most common concerns of this hormone. Contrary to what many believe, circulating DHT may not be directly responsible for hair loss. When hair follicles come in contact with excess amounts of DHT, they will eventually die. Yet, the ratio of DHT/testosterone hasn’t been found to be a determining factor to balding, but free-testosterone / total-testosterone is. Round testosterone cannot be reduced by the 5-ar-reductase enzymes in the scalp, but free-testosterone can and will definitely lead to hair loss. Men who experience hair loss exhibit a significant reduction in sex hormone binding globulin, leading to a higher free-testosterone/ total-testosterone ratio. As men age, their androgen levels and sex hormone binding globulin decrease and localized 5-ar reductase enzymes increase in the scalp, and this leads to hair loss. It can be said that higher levels of DHT do not cause hair loss, but increased levels of the 5-ar reductase enzyme and unbound testosterone does.
We describe a simple procedure for the microassay of 3 alpha-hydroxysteroid oxidoreductase in homogenates of rat brain. This enzyme converts dihydrotestosterone to 3 alpha-androstandiol. We have mapped the distribution of the enzymatic activity in 14 regions of the rat brain. The highest activities were observed in homogenates of olfactory bulb (51/nmol/mg protein/h) and olfactory tubercle (29 nmol/mg protein/h). Substantially lower values were seen in the other brain regions, including thalamus, caudate nucleus, frontal cortex, hippocampus, hypothalamus, and preoptic area (6-20 nmol/mg protein/h).