Specialized cells in the testis, called Leydic cells, make testosterone (referred to as one of the male hormones). An adult male produces approximately five grams of testosterone per day. Testosterone releases in pulses or bursts. There is a daily pattern to the secretion of testosterone, with a peak occurring early in the morning and a low point in the late evening.
Only certain cells have receptors for testosterone and some of these cells later convert the testosterone into Dihydro-testosterone (DHT). DHT is three times as potent as the testosterone itself. Interestingly, the testosterone can also be converted into estrogens (the main female hormone). This occurs particularly in fat cells.
Most testosterone in the body is bound or "attached" to proteins. Thirty percent is bound to a type of protein known as sex hormone-binding globulin (SHBG). The testosterone binds very tightly to SHBG, which has a tendency to increase as men age. The remaining testosterone is bound much less tightly to other proteins in the blood, the most prevalent of which is albumin. Two percent of the testosterone is unbound (not attached to any other protein) and is called free testosterone. Free and albumin-bound portions of testosterone make up the measure known as "bioavailable testosterone." This is the testosterone that is seen in the tissue and that has the most effect on the body. Thus, any change will affect the total amount of available testosterone. The amount of SHBG or blood proteins will affect the amount of available testosterone and will have an effect on the body.
As men get older, their SHBG increases, leaving less available testosterone. Other hormones can also affect SHBG. Elevated female hormones and thyroid hormones will increase SHBG, which will then, in turn, affect the bioavailable testosterone.
Since testosterone is so important, when a person has a deficiency, testosterone supplements can be greatly beneficial. Working with a specialist will allow a person to achieve the correct testosterone level without receiving excess testosterone. Men supplementing their testosterone secretions must be carefully monitored to prevent negative effects.
