Structure:
Testosterone, the major androgen hormone secreted by the testis is rapidly
bound in the blood to sex-hormone binding globulin. This protein, produced
by the liver under the action of estradiol,
serves to keep the hormone inactive until it is taken into target
tissues by selective absorption of the protein-hormone complex with
a receptor. In the cell, testosterone is
metabolized to a more potent hormone, dihydrotestosterone, by the 5-alpha
reductase. Thereafter, the nuclear DNA binds the steroid for furter activation
of the cell. Circulating testosterone decreases the release of GnRH
by the hypothalamus, and LH
by the adenohypophysis.
Function:
Testosterone is a potent male hormone that promotes sexual maturity, the
development of secondary sex features, and sex behavior. It also maintains
the genital organs in a functional state, capable of reproduction.
