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Question 486
Endocrinology → General
Classification
Question
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A woman has a physiological increase in circulating oestrogen. This increases hepatic production of sex hormone-binding globulin (SHBG). Which hormone has the greatest proportion bound to SHBG under normal conditions?
Question Stem
Select the single best answer.
Options
A
Oestrogen
B
Dehydroepiandrosterone
C
Dihydrotestosterone
D
Testosterone
E
Androstenedione
Explanation
Testosterone has the greatest proportion bound to SHBG: approximately 69%. By comparison, approximately 40% of oestrogen, 28% of dihydrotestosterone and 8% each of dehydroepiandrosterone and androstenedione are SHBG-bound. Only the free, unbound fraction is available for receptor binding and biological activity.
Option Validity
A) Approximately 40% of oestrogen is bound to SHBG, less than the proportion of testosterone.
B) Approximately 8% of dehydroepiandrosterone is bound to SHBG.
C) Approximately 28% of dihydrotestosterone is bound to SHBG.
E) Approximately 8% of androstenedione is bound to SHBG.
Further Reading
Saxena, MRCOG-1 Basic Sciences, Endocrinology: General Endocrinology, sex hormone-binding globulin and hormone transport, pp. 300–301.