Inside a male body, the most important androgens are the steroids, and testosterone is the most important androgen synthesized by the testicles and released human plasma. In male’s blood there can be found other lower quantities of androgens like dihydrotestosterone- DHT.
In the average male body, the plasmatic level of testosterone is approximately 7 nanograms. /ml, (24.3 nanomole/l) and DHT level is 0.45 ng/ml (1.56 nmol/l), higher, compared to the testosterone and DHT plasmatic levels in an average woman’ body, 0.45 ng/ml (1.56 nmol/l) and 0.20 ng/ml (0.69 nmol/l); moreover, in females DHT has blood flow regulatory function.
Androstenedione is also secreted by the Leyding cells, but it only serves as plasmatic precursor for estrogens. Furthermore, inside the normal male body there are secreted 17-hydroxiprogesterone, and progesterone but their physiological function is unknown.
Approximately 95% of the sanguine testosterone is produced by testicular Leyding cells.
Testosterone Transport and Metabolism
Testosterone transport inside human blood is not a simple process, because steroids have a hydrophobic structure and are insoluble in aqueous solutions. Its transport is made by tying it to a specific plasmatic protein called: testosterone-estradiol-binding globulin, TeBG, this protein differs from cortisol-binding globulin (that binds and transports cortisol, corticosterone and progesterone). Estrogens support (about 10 times) increase of TeBG circulatory concentration while testosterone decreases TeBG level down to half. 30% of the plasmatic testosterone is bind to TeBG, only 3% are free, and the rest of the testosterone concentration is bind to albumin and other sanguine peptides.
Inside the brain and the mammary glands testosterone is turned into a strong estrogen called estradiol. Its metabolic function is to elevate male estrogen circulatory parameters. The amplification of testosterone activity is conveyed by 5-reductaza enzyme activity which transforms testosterone in dihydrotestosterone-DHT. Furthermore, DHT is produced in the masculine reproductive tract and is linked with absorptive modulator and secretor epididymal activity. At epididymal and skin levels, DHT stimulates cellular division. Other testosterone derivates, including 5-DHT, influence the erythrocytes production inside the bone marrow. About 60% of male’s testosterone production is metabolized inside the liver and turned into inactive radicals.
Hypophysis- Leyding cells axis, the local and hormonal control
LH sanguine level is the main androgen and testosterone synthesis regulator. Increased LH levels leads to Leyding cells hypertrophy and testosterone secretion. Decreased LH level is determined by pituitary gland secretions. Pituitary activity is directly responsible of the plasmatic level of testosterone, and if the testosterone level downfalls it automatically triggers pituitary negative feedback-increased LH secretion. Due to the control exerted by GnRH upon LH secretion, the testicles, hypophysis and hypothalamus form a functional unit involved in spermatogenesis regulation.
It is very important to understand the intricate interaction between Leyding and Sertoli cells. It has been scientifically proven that the type of FSH which directly affects Sertoli cells has also a substantial effect upon Leyding cells leading to hypertrophy and hyperplasia as the number of LH receptors increases.