Woerdeman J, Kaufman JM, de Ronde W. In young men, a moderate inhibition of testosterone synthesis capacity is only partly compensated by increased activity of the pituitary and the hypothalamus.
Clin Endocrinol (Oxf) 2010;
72:76-80. [PMID:
19473182 DOI:
10.1111/j.1365-2265.2009.03624.x]
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Abstract
CONTEXT
The classical interpretation of the feedback regulation of the male hypothalamo-pituitary-gonadal axis predicts that a partial inhibition of testosterone (T) synthesis will result in a compensatory rise in LH secretion. The question arises as to whether such a compensation is complete or that decreased T synthesis may result in a lower plasma T concentration.
OBJECTIVE
To investigate whether a moderate inhibition of T synthesis capacity will be fully compensated by increased LH secretion. DESIGN, SUBJECTS AND INTERVENTIONS: In nine young healthy men, we partially inhibited T synthesis capacity using ketoconazole (KTZ) 100 mg four times daily. On day -6 (1 week prior to KTZ intake), days 1 and 8 of KTZ administration blood was drawn [07:00 h (t(1)), 10:00 h (t(2)), 13:00 h (t(3))] for evaluation of T, LH, oestradiol (E2), 17-OH-progesterone (17OHP), progesterone (PR) and sex hormone binding globulin (SHBG). On day 8, 5000 IU of hCG were administered to evaluate the maximal T secretion under KTZ.
RESULTS
Administration of KTZ resulted in an acute, moderate but significant decrease of plasma T concentration. On day 8, plasma LH, 17OHP and PR were elevated relative to day -6 and day 1, but mean T was still lower compared to day -6. Mean E2 and SHBG were only slightly affected by KTZ. After stimulation by hCG, plasma T was restored to its baseline level.
CONCLUSION
These results argue against the assumption that a moderate decline in T synthesis capacity will be compensated completely by increased LH secretion.
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