Characterization of Plasma Androgens

CHARACTERIZATION OF PLASMA ANDROGENS

In males, testosterone is the principal circulating andro-gen, and the testes are the principal source. Although the adrenals are capable of androgen synthesis, less than 10% of the circulating androgens in men are pro-duced in the adrenals. Testosterone is synthesized by Leydig cells of the testes at the rate of about 8 mg/24 hours, providing a plasma concentration of 0.5 to 0.6 g/dL. In females, the ovaries contribute approxi-mately one-third of the total androgens synthesized, while the adrenals contribute the rest.

Androstenedione, dehydroepiandrosterone (DHEA), and dehydroepiandrosterone sulfate (DHEA-S) are other mildly androgenic compounds of secondary im-portance in males and females. The gonads and the ad-renal cortex are capable of secreting androstenedione and DHEA, while DHEA-S is secreted primarily by the adrenal.

Concentrations of plasma testosterone and other androgens vary throughout the day in both sexes; whether such variation is simply random or fits a re-peatable diurnal pattern is a matter of debate. Com-pared with the diurnal variation seen with cortisol, plasma testosterone concentrations are reasonably con-stant. Plasma androgen concentrations also vary greatly in women through the menstrual cycle, with peak levels seen in the luteal phase.