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).
Allopurinol (al-oh-PURE-i-nole) is used to treat chronic gout (gouty arthritis). This condition is caused by too much uric acid in the blood. This medicine works by causing less uric acid to be produced by the body. Allopurinol will not relieve a gout attack that has already started. Also, it does not cure gout, but it will help prevent gout attacks. However, it works only after you have been taking it regularly for a few months. Allopurinol will help prevent gout attacks only as long as you continue to take it. Allopurinol is also used to prevent or treat other medical problems that may occur if too much uric acid is present in the body. These include certain kinds of kidney stones or other kidney problems. Certain medicines or medical treatments can greatly increase the amount of uric acid in the body. This can cause gout or kidney problems in some people. Allopurinol is also used to prevent these problems, and can be given as either a tablet or an injection if necessary.
The mechanisms of mineralization are not fully understood. Fluorescent, low-molecular weight compounds such as tetracycline or calcein bind strongly to bone mineral, when administered for short periods. They then accumulate in narrow bands in the new bone.  These bands run across the contiguous group of bone-forming osteoblasts. They occur at a narrow (sub- micrometer ) mineralization front. Most bone surfaces express no new bone formation, no tetracycline uptake and no mineral formation. This strongly suggests that facilitated or active transport , coordinated across the bone-forming group, is involved in bone formation, and that only cell-mediated mineral formation occurs. That is, dietary calcium does not create mineral by mass action.