Definition:

ANDROGEN = male producing. Establishes and maintains adult sexual function and fertility.

Mechanism:

Androgens act upon a large number of reproductive and non-reproductive target tissues, including bone, adipose tissues, skeletal muscle, brain, prostate, liver, and kidney. The actions of androgens are mediated by one molecular species of androgen with a single mode of action which, is through transcriptional activation of androgen response elements in different target genes.

Some aspects of the tissue specificity of androgen action can be accounted for by the local conversion of testosterone to specific metabolites including dihydrotestosterone (DHT) and estradiol.

Testosterone is a target hormone itself as well as a circulating prohormone for several target tissues that have the converting enzymes 5alpha-reductase and aromatase. Testosterone is derived from cholesterol after undergoing a series of enzymatic reactions that modify the basic cholesterol molecule.

The androgen receptor in skeletal muscle is saturated wit the physiological concentrations of testosterone present. Due to the decreased amount of 5alpha-reductase activity in the skeletal muscle, testosterone and possible circulating DHT appear to be the key hormones for androgen action.

Normal levels of testosterone reach a plateau once a physiological concentration is exceeded (male hormone replacement), with supraphysiological doses (male contraception), the anabolic effects may be evoked through a separate mechanism independent of the androgen receptor such as a anticatabolic effect on an antiglucocorticoid action.

Mechanism of steroid hormone

Transport of hormones from secretory vesicles, through the bloodstream to the target cell

Secretion of hormones to target cells