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.
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