TESTOSTERONE

Clinical Significance:

Testosterone is the most important representative of the male sex hormones collectively called androgens. The male gonads (testes) produces testosterone, under the influence of a hormone released from the pituitary gland called luteinizing hormone (LH), and the adrenal gland produces testosterone in small amounts. In women, 50% comes from the ovaries, with the rest coming from the adrenal gland or conversion in the tissues. The signals are particularly strong in the early morning which accounts for the higher testosterone levels. By the late evening the levels of testosterone can fall by 50 percent. Testosterone production increases rapidly at the onset of puberty, but starts to drop the nearer you get to 30 years of age. During puberty, testosterone levels are at their lifetime peak. A high intratesticular level of testosterone is an absolute prerequisite for sperm production. In men, it has been well established that mean Testosterone levels drop progressively with age.

Periodically the hypothalamus releases pulses of gonadotrophin-releasing hormone (GnRH) into the hypophyseal circulation, which supplies the hypothalamus and anterior pituitary. The GnRH stimulates the anterior pituitary to produce and release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). At the testicles LH and FSH interact with their target tissue (LH, Leydig cells; FSH, Sertoli cells) receptors located on the respective cell membranes.

In the Leydig cells, there is mobilization of steroid precursors, in particular the activation of pregnenolone synthesis from cholesterol. Pregnenolone serves as the parent compound from which testosterone is derived. An additional participant in these regulatory events is the anterior pituitary hormone prolactin, which in low concentrations acts as a potentiator of LH at the Leydig cells. Synthesized testosterone diffuses from the Leydig cells into the testicular vascular system and/or into adjacent testicle compartments containing the Sertoli cells. In the Sertoli cells, testosterone plays an essential role in the facilitation of the spermatogenesis process.