Androgen Supplementation in Older Women: Too Much Hype, Not Enough Data: Part 3
BIOLOGY OF TESTOSTERONE PRODUCTION IN MENSTRUATING, POSTMENOPAUSAL AND OLDER WOMEN
Table 1 lists the adrenal androgens, their potencies and concentrations in serum for premenopausal
and post-menopausal women.
Adrenal and ovarian production of androgens in healthy, young menstruating women collectively contributes to secretion of approximately 300 μg testosterone daily into the general circulation. Approximately, half of the circulating testosterone is derived from ovarian secretion. The adrenal gland produces testosterone precursors, dehydroepiandrosterone (DHEA),
dehydroepiandrosterone sulfate (DHEAS) and androstenedione, whose peripheral conversion to
testosterone contributes the remaining 50 percent of circulating testosterone.
Although the current dogma assumes approximately equal contribution from the ovaries and the adrenal glands, these assumptions may not be entirely correct. The data from studies in which testosterone production rates were measured after suppression of hypothalamic-pituitary-adrenal axis with dexamethasone administration are suspect because dexamethasone is known to also suppress ovarian steroidogenesis.
DHEAS is secreted entirely from the adrenal gland, while DHEA is secreted by both the adrenal glands and the ovaries. The majority of circulating DHEA is derived from peripheral conversion of DHEAS. The metabolism of DHEA(S) into bioactive sex steroids may occur in many tissues, including adipose tissue, bone, muscle, prostate, breast, skin, brain, ovary, testes and the liver. Circulating androstendione is derived equally from secretion by zona fasciculata of the adrenal glands and stromal cells within the ovary.
Androgen Levels During The Menstrual Period
In regularly ovulating women, the plasma levels of testosterone and androstenedione rise gradually during the follicular phase to reach their highest levels in the pre-ovulatory phase, with a second rise in androstenedione during the late luteal phase. Serum testosterone concentrations during the mid-follicular phase are not significantly different from those in mid-luteal phase.
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July 24, 2009 - 7:27amThis Comment