Basic Intracellular Mechanism of Action of Testosterone
Most of the effects of testosterone result basically from increased rate of protein formation in the target cells. This has been studied extensively in the prostate gland, one of the organs that is most affected by testos-terone. In this gland, testosterone enters the prostatic cells within a few minutes after secretion. Then it is most often converted, under the influence of the intracellular enzyme 5a-reductase, to dihydrotestos-terone, and this in turn binds with a cytoplasmic “receptor protein.” This combination migrates to the cell nucleus, where it binds with a nuclear protein and induces DNA-RNA transcription. Within 30 minutes, RNA polymerase has become activated and the con-centration of RNA begins to increase in the prostatic cells; this is followed by progressive increase in cellu-lar protein. After several days, the quantity of DNA in the prostate gland has also increased and there has been a simultaneous increase in the number of prostatic cells.
Testosterone stimulates production of proteins virtually everywhere in the body, although more specifically affecting those proteins in “target” organs or tissues responsible for the development of both primary and secondary male sexual characteristics.
Recent studies suggest that testosterone, like other steroidal hormones, may also exert some rapid, non-genomic effects that do not require synthesis of new proteins. The physiological role of these nongenomic actions of testosterone, however, has yet to be determined.