Testosteronsubstitution Die Urologie Springer Nature Link

Since testosterone levels decrease as men age, testosterone is sometimes used in older men to counteract this deficiency. As the metabolism of testosterone in males is more pronounced, the daily production is about 20 times greater in men. In humans and most other vertebrates, testosterone is secreted primarily by the testicles of males and, to a lesser extent, the ovaries of females. It exerts its action through binding to and activation of the androgen receptor.  Clenbuterol Veilig Kopen  of these ubiquitous steroids in a wide range of animals suggest that sex hormones have an ancient evolutionary history.
Testosterone and the classical nuclear androgen receptor first appeared in gnathostomes (jawed vertebrates). They named the hormone testosterone, from the stems of testicle and sterol, and the suffix of ketone. Suffering the ridicule of his colleagues, he abandoned his work on the mechanisms and effects of androgens in human beings.
Men who watch sexually explicit films also report increased motivation and competitiveness, and decreased exhaustion.  Тестостерон ПУ (Undecanoate) Цена  who watch a sexually explicit movie have an average increase of 35% in testosterone, peaking at 60–90 minutes after the end of the film, but no increase is seen in men who watch sexually neutral films. The plasma levels of various steroids significantly increase after masturbation in men and the testosterone levels correlate to those levels.
The number of Leydig cells in turn is regulated by luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Testosterone is also synthesized in far smaller total quantities in women by the adrenal glands, thecal cells of the ovaries, and, during pregnancy, by the placenta. In the final and rate limiting step, the C17 keto group androstenedione is reduced by 17β-hydroxysteroid dehydrogenase to yield testosterone. Testosterone has been found to act as an antagonist of the TrkA and p75NTR, receptors for the neurotrophin nerve growth factor (NGF), with high affinity (around 5 nM).  Anavar černý trh , via its active metabolite 3α-androstanediol, is a potent positive allosteric modulator of the GABAA receptor.
An additional 40% of testosterone is metabolized in equal proportions into the 17-ketosteroids androsterone and etiocholanolone via the combined actions of 5α- and 5β-reductases, 3α-hydroxysteroid dehydrogenase, and 17β-HSD, in that order. Approximately 50% of testosterone is metabolized via conjugation into testosterone glucuronide and to a lesser extent testosterone sulfate by glucuronosyltransferases and sulfotransferases, respectively. The amount of testosterone synthesized is regulated by the hypothalamic–pituitary–testicular axis (Figure 2). In addition, the amount of testosterone produced by existing Leydig cells is under the control of LH, which regulates the expression of 17β-hydroxysteroid dehydrogenase.
In addition to conjugation and the 17-ketosteroid pathway, testosterone can also be hydroxylated and oxidized in the liver by cytochrome P450 enzymes, including CYP3A4, CYP3A5, CYP2C9, CYP2C19, and CYP2D6. A small portion of approximately 3% of testosterone is reversibly converted in the liver into androstenedione by 17β-HSD. In the hepatic 17-ketosteroid pathway of testosterone metabolism, testosterone is converted in the liver by 5α-reductase and 5β-reductase into 5α-DHT and the inactive 5β-DHT, respectively. The conjugates of testosterone and its hepatic metabolites are released from the liver into circulation and excreted in the urine and bile. Androsterone and etiocholanolone are then glucuronidated and to a lesser extent sulfated similarly to testosterone.