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).
Laws and Penalties: Concerns over growing illegal AAS abuse by teenagers, and many of the just discussed long-term effects, led Congress in 1991 to place the whole AAS class of drugs into Schedule III of the Controlled Substances Act (CSA). Under this legislation, AAS are defined as any drug or hormonal substance, chemically and pharmacologically related to T (other than estrogens, progestins, and corticosteroids) that promotes muscle growth. The possession or sale of AAS without a valid prescription is illegal. Since 1991, simple possession of illegally obtained AAS carry a maximum penalty of one year in prison and a minimum $1,000 fine if this is an individual’s first drug offense. The maximum penalty for trafficking (selling or possessing enough to be suspected of selling) is five years in prison and a fine of $250,000 if this is the individual’s first felony drug offense. If this is the second felony drug offense, the maximum period of imprisonment and the maximum fine both double. While the above listed penalties are for federal offenses, individual states have also implemented fines and penalties for illegal use of AAS. State executive offices have also recognized the seriousness of AAS abuse and other drugs of abuse in schools. For example, the State of Virginia enacted a law that will allow student drug testing as a legitimate school drug prevention program (48, 49).
As demonstrated in progesterone receptor-deficient mice, the physiological effects of progesterone depend completely on the presence of the human progesterone receptor (hPR), a member of the steroid-receptor superfamily of nuclear receptors. The single-copy human (hPR) gene uses separate promoters and translational start sites to produce two isoforms, hPR-A and -B, which are identical except for an additional 165 amino acids present only in the N terminus of hPR-B.  Although hPR-B shares many important structural domains with hPR-A, they are in fact two functionally distinct transcription factors, mediating their own response genes and physiological effects with little overlap. Selective ablation of PR-A in a mouse model, resulting in exclusive production of PR-B, unexpectedly revealed that PR-B contributes to, rather than inhibits, epithelial cell proliferation both in response to estrogen alone and in the presence of progesterone and estrogen. These results suggest that in the uterus, the PR-A isoform is necessary to oppose estrogen-induced proliferation as well as PR-B-dependent proliferation.