[Testosterone--effects, metabolism and genetic determination]

Testosterone (C19H28O2), the main testicular hormone, is 19-carbonic steroid substance with -OH group in position 17. Precursor for its synthesis is cholesterol, or possibly androstendione released by adrenal cortex. Testosterone is produced in smooth endoplasmatic reticulum of Leydig cells of testes. Apart from testes it is also produced in adrenal cortex, liver, kidneys, in fat and muscle tissue, even though in smaller extent--around 5% (Bidlingmaier, F. et al., 1986). Approximately 4-9 mg (13.9-31.2 nmol/l) of testosterone is daily produced in healthy men. Absolute majority, around 99% from overall plasmatic testosterone is bound to albumin, erythrocytes, but mainly to sex hormone binding globulin (SHBG) (Diver, M.J. et al., 2003). Only small proportion (1-2%) of testosterone circulates as free fraction (Ostatníková, D., 2003). Production and secretion of the main androgen in testes is regulated by well known and accepted axis of hypothalamus, hypophysis and testes. Testosterone and its metabolite dihydrotestosterone can influence the expression of genes, development of masculine type of habitus and behavior, acting via androgen receptor (AR) (Zitzmann, M. and Nieschlag, E., 2003). Testosterone can affect also via its metabolites, whose production is conditioned by enzymes. In peripheral tissues is testosterone converted via aromatase to estradiol and via 5alpha-reductase to dihydrotestosterone (Weber, K.S. et al., 1999).