Human Growth Hormone is an injectable hormone that can be administered subcutaneously or intramuscularly. When injected subcutaneously, HGH carries a bioavailability of approximately seventy-five percent. When injected intramuscularly, HGH carries a bioavailability of approximately sixty-three percent. The mode of administration will also affect the half-life of the Somatropin hormone. When injected subcutaneously, it will carry a half-life of approximately hours. When injected intramuscularly, it will carry a half-life of approximately hours. While this is a rather short half-life regardless of the mode of administration, keep in mind the total effects far outlast these numbers due to the pronounced and significant increases in IGF-1 production that stretch far past the twenty-four hour mark.
Testosterone is responsible for many actions related to the reproductive system, as well. It is the hormone that is chiefly implicated in determining what sex a fetus will become in the womb. After birth, testosterone directs the development of sexual characteristics during adolescence. Bodybuilders, who often use anabolic steroids, rely on the synthetic steroid’s molecular similarity to testosterone to build muscle mass . Steroid hormones are also used in medical applications to treat hormonal disorders and deficiencies. The hormones have been proven to be relatively safe in these medical applications, but overuse has been linked to baldness , certain types of cancer, and liver disease.
Because steroids are lipophilic, they diffuse easily through the cell membranes, and therefore have a very large distribution volume. In their target tissues, steroids are concentrated by an uptake mechanism which relies on their binding to intracellular proteins (or " receptors ", see below). High concentration of steroids are also found in adipose tissue, although this is not a target for hormone action. In the human male, adipose tissue contains aromatase activity, and seems to be the main source of androgen-derived estrogens found in the circulation. But most of the peripheral metabolism occurs in the liver and to some extent in the kidneys, which are the major sites of hormone inactivation and elimination, or catabolism (see below).