Does sex hormone-binding globulin play a role in the transport of estradiol in vivo?
The distribution of estradiol and testosterone into sex hormone-binding globulin (SHBG)-bound, albumin-bound, and unbound fractions in whole serum under equilibrium conditions at 37 degrees C is described in women with normal menstrual cycles, pregnant women, and newborn infants. The percentage of estradiol bound to SHBG was determined by equilibrium dialysis at 37 degrees C. Whole serum, 0.1 ml, was dialyzed against 0.1 ml of the same serum heated at 60 degrees C for 1 hour (a procedure shown to denature SHBG but not to affect albumin). The percentage of unbound estradiol in whole serum was measured by dialyzing native serum against an isosmotic dextran solution. Testosterone binding was studied similarly. Our findings show that SHBG is an important binder of estradiol in both pregnant and nonpregnant women. However, estradiol binding by SHBG is undetectable in the newborn infant. Testosterone is significantly bound to SHBG under all circumstances. We conclude that SHBG does play a role in the transport of estradiol in women, particularly in pregnancy.
D000328:Adult; D004958:Estradiol / Q000097:blood / Q000378:metabolism*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008598:Menstruation; D011247:Pregnancy; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000378:metabolism*
D012709:Serum Albumin; D012738:Sex Hormone-Binding Globulin; D013739:Testosterone; D004958:Estradiol