OK found some interesting reading on the interactions between some of the different androgens, and what the different hormones do?
In humans testosterone is the primary muscle-building hormone. Its activity is likewise highly anabolic, more so than any other naturally occurring steroid hormone. In fact despite the development of many synthetic analogues of testosterone, athletes generally still consider our base androgen to be the most potent agent for building muscle tissue. This clearly explains the great popularity of injectable testosterone compounds in virtually every corner of the world. Testosterone is also a powerful androgen, primarily due to its peripheral conversion to the more active steroid dihydrotestosterone (DHT). Dihydrotestosterone is beneficial in that it help support nervous system functionality, which is tied closely to strength and tissue gains. However its strong activity and local production in areas such as the skin and scalp also give it the potential to induce androgenic side effects such as oily skin, acne, body/facial hair growth and male pattern hair loss (for those with a genetic predisposition). Though normally tolerable, such side effects can become troublesome as the dosage of testosterone gets very high.
In men testosterone is also the primary substrate for the synthesis of estradiol (a potent estrogen). In normal physiological levels estradiol production does not produce noticeable changes to the physique. However when testosterone levels become exaggerated due to heavy supplementation, it may potentially increase the deposition of body fat, tissue fluid retention and possibly stimulate the growth of female breast tissue (gynecomastia). When athletes use testosterone in moderate amounts these side effects are typically not noticed. Again however, their possibility does place a limit on the dosing of testosterone without some form of ancillary drug to combat these side effects. For this reason testosterone is often used as a base in a steroid cycle, to be stacked with agents less apt to convert to estrogens.
