Given the wide spectrum of androgen actions, it is reasonable to expect the intracellular processes mediating these diverse effects to vary among target tissues. The currently accepted hypothesis of androgen action in male sex accessory organs is depicted in Fig. 63.4. Testosterone diffuses from the blood across the plasma membrane of the sex accessory organ cell, where it is rapidly metabolized to DHT and androstanediol. In many sex accessory organs, DHT, rather than testosterone, is the primary intracellular androgen and is more potent than testosterone. Once formed, DHT preferentially binds to a receptor protein in the nucleus. This DHT-receptor complex is subsequently activated and binds to proteins on the nuclear matrix. Following this interaction, RNA synthesis results in enhanced protein synthesis and cellular metabolism. If sufficient androgen stimulation occurs, DNA synthesis and cellular division begin.
Non-sex accessory tissues also are targets for the protein anabolic actions of androgens. These tissues possess lower levels of endogenous hormone, minimal 5a-reductase activity, and lower concentrations of specific androgen receptors. The protein anabolic actions are probably mediated by an interaction with the androgen receptor.
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