Testosterone also

Testosterone also plays a significant albeit complex role in erectile function. Testosterone is responsible for much of a man s libido. With low serum concentrations, libido declines. Additionally, testosterone helps with stabilization of intracavernosal levels of nitric oxide synthase, the enzyme responsible for triggering the nitric oxide cascade. Interestingly, some patients with low or borderline low serum concentrations of testosterone will have normal erectile function, while some with normal levels will have dysfunction. 

Steroids are a class of lipids that have in common a system of four linked carbon rings. Cholesterol, shown in Figure 13.14, is the most abundant steroid by far, and it serves as the starting material for the biosynthesis of most all other steroids, including the sex hormones estradiol and testosterone, also shown in Figure 13.14. Hormones are chemicals produced by one part of the body to influence other parts of the body. For example, estradiol, produced by the ovaries, and testosterone, produced by the testes, are responsible for the development of secondary sex characteristics in other parts of the body. Cholesterol is... 

As mentioned before, circulatory levels of testosterone also effect HPTA function, so I should not list it as a characteristic unless I also list pretty much every other sex-hormone as well. 

HCG was combined with Clomiphene (Clomid) sometimes, or Clomiphene was used after HCG administration. This is because Clomiphene acts by affecting the hypothalamus and pituitary (hypophysis) and regenerating the whole regulating system, while HCG only "imitates" LH, thus stimulating the leydig cells in the testes to produce natural testosterone. ( Also see HCG)... 

For years, it was believed that the free fraction of testosterone represented the biologically active fraction. However, it is now thought that dissociation of protein-bound testosterone also occurs within a capillary bed. In studies of tissue delivery m vivo, nearly all of the albumin-bound testosterone was available for tissue uptake. Therefore, the bioavailable testosterone is equal to about 35% of the total, or the free plus the albumin-bound. The albumin-bound fraction is referred to as the non-SHBG-bound fraction or weakly bound fraction. 

Szulc et al. (2005) reported that skeletal muscle mass was correlated positively with bone mineral content and bone mineral density in the Mediterranean Intensive Oxidant Study (MINOS). MINOS was a prospective study of osteoporosis and its determinants that showed that men with the least skeletal mass also had increased risks of falls due to impaired static and dynamic balance. The relative importance of muscle compared with hormonal and other nutritional effects on bone health may be argued in the MINOS study because factors such as dietary protein, insulin growth factor, and testosterone also affect bone directly, but chronically low muscle mass may provide a visible indicator of bone mass and bone density risk. Osteopenia and osteoporosis are seen as problems in elderly people. In countries with shortened life spans, bone health issues may go unnoticed. 

The biological effects of testosterone can be considered by the receptor it activates and by the tissues in which its effects occur at various stages of life. Testosterone can act as an androgen either directly, by binding to the AR, or indirectly by conversion to dihydrotestosterone, Testosterone also can converted to estradiol, which activates the estrogen receptor (Figure 58 ). 

The major effect of androgenic hormones—in addition to development and maintenance of normal male characteristics—is an anabolic action that involves increased muscle size and strength and increased red blood cell production. Excretion of urea nitrogen is reduced, and nitrogen balance becomes more positive. Testosterone also helps maintain normal bone density. 

Testosterone also has been compressed into 75- or 200-mg testosterone pellets, which release 1 to 3 mg of testosterone/day. One to two pellets are implanted under the skin, typically in the buttocks or abdomen, through a special needle under local anesthesia. They usually are replaced every 3 to 4 months. Although the pellets have been used experimentally for approximately 15 years, the use of testosterone pellets is not approved by the U.S. Food and Drug Administration. Reportedly, the pellets offer the advantage of very consistent testosterone blood levels. Some users have reported problems with the pellets working their way out from under the skin. 

Osteoporosis is connected especially with a diminished estrogen production in advanced age. Estrogens stimulate the osteoblasts and prevent calcium deposits in other tissues. They also stimulate nitrogen retention and increase protein synthesis in the bone matrix. Testosterone also has the latter activities. 

Transdermal patches of testosterone also have problems A fraction of the testosterone is metabolized in the skin and converts to dihydrotestosterone. This metabolic side product can cause swelling of the prostate gland. Testosterone patches are placed on the body where the rate of absorption is highest, but this unfortunately can cause the metabolic product, dihydrotestosterone, to create side effects. Improved patches can be placed in areas where metabolized dihydrotestosterone is minimized. Reduction of transdermal absorption by the changed application area can be overcome by the addition of an absorptive aid. 

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