Testosterone is the most important representative of the male sex hormones collectively called androgens. Using cholesterol as a base, the male gonads (testes) produce between 4 and 10 mg of testosterone per day. Testosterone itself is responsible for three major functions in animals.
1) The development of secondary male sex characteristics also called the androgenic functions of testosterone. Some examples of these characteristics are increased growth of body hair, beard growth, deep voice, increased production of sebaceous glands, development of the penis, aggressiveness, sexual behavior, libido, and the maturation of sperm.
2) Promotion of the protein biosynthesis that are responsible for the highly anabolic characteristics of testosterone. This is a pretty important function. It accelerates muscle buildup, increases the formation of red blood cells, speeds up regeneration, and speeds up recovery time after injuries or illness. It also stimulates the entire metabolism which results in the burning of bodyfat.
3) Inhibition of the gonad regulating cycle, including the hypothalamohypophysial testicular axis, which regulates the amount of testosterone produced in the organism. If the testosterone levels in the blood is high, the testes will signal the hypothalymus to release less LHRH (leutenizing hormone releasing hormone). Thus the hypophysis releases less gonadotropin LH (leutenizing hormone) and FSH (folic stimulating hormone). Consequently, the Leydig's cells in the testes reduces the production of testosterone. In other words, if you have too much testosterone, your body will tell itself to reduce or even stop production of it until it is back down to its normal levels.
During puberty, testosterone levels are at their lifetime peak. They begin to decline around the age of 23. This is where testosterone therapy comes into play. Many men and women suffer from the lack of important hormones and testosterone replacement therapy is simply the most effective way to combat the signs of aging.