Nettle Root
About 90% of testosterone is produced by the testes, the remainder by the adrenal glands. Testosterone functions as an aphrodisiac hormone in brains cells, and as an anabolic hormone in the development of bone and skeletal muscle. But testosterone that becomes bound to serum globulin is not available to cell receptor sites and fails to induce a libido effect. It is, therefore, desirable to increase levels of "free testosterone" in order to ignite sexual arousal in the brain.
As discussed already, a hormone that controls levels of free testosterone is called sex hormone-binding globulin (SHBG). When testosterone binds to SHBG, it loses its biological activity and becomes known as "bound testosterone," as opposed to the desirable "free testosterone." As men age past year 45, SHBG's binding capacity increases almost dramatically-by 40% on average-and coincides with the age-associated loss of libido.
Some studies show that the decline in sexual interest with advancing age is not always due to the amount of testosterone produced, but rather to the increased binding of testosterone to globulin by SHBG. This explains why some older men who are on testosterone replacement therapy do not report a long-term aphrodisiac effect. That is, the artificially administered testosterone becomes bound by SHBG, and is not bioavailable to cellular receptor sites where it would normally produce a libido-enhancing effect.
It should be noted that the liver also causes testosterone to bind to globulin. This liver-induced binding of testosterone is worsened by the use of sedatives, anti-hypertensives, tranquilizers and alcoholic beverages. The overuse of drugs and alcohol could explain why some men do not experience a libido-enhancing effect when consuming drugs and plant-based aphrodisiacs. An interesting review, "How Desire Dies" (Nature, 381/6584, 1996), discusses how frequently prescribed drugs, such as beta-blockers and antidepressants, cause sexual dysfunction. Prescription drugs of all sorts have been linked to inhibition of libido.
Logically, one way of increasing libido in older men would be to block the testosterone-binding effects of SHBG. This would leave more testosterone in its free, sexually activating form.
A highly concentrated extract from the nettle root provides a unique mechanism for increasing levels of free testosterone. Recent European research has identified constituents of nettle root that bind to SHBG in place of testosterone, thus reducing SHBG's binding of free testosterone. As the authors of one study state, these constituents of nettle root "may influence the blood level of free, i.e. active, steroid hormones by displacing them from the SHBG bindings site."
The prostate gland also benefits from nettle root. In Germany, nettle root has been used as a treatment for benign prostatic hyperplasia (enlargement of the prostate gland) for decades. A metabolite of testosterone called dihydrotestosterone (DHT) stimulates prostate growth, leading to enlargement. Nettle root inhibits the binding of DHT to attachment sites on the prostate membrane.
Nettle extracts also inhibit enzymes such as 5 alpha reductase that cause testosterone to convert to DHT. It is the DHT metabolite of testosterone that is known to cause benign prostate enlargement, excess facial hair and hair loss at the top of the head.
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