Sex hormone-binding globulin changes during the menstrual cycle.

Area of Science:

• Endocrinology
• Reproductive Biology
• Women's Health

Background:

• Sex hormone-binding globulin (SHBG) production is known to be stimulated by estrogen.
• Previous studies have not demonstrated consistent changes in SHBG levels throughout the menstrual cycle.

Purpose of the Study:

• To investigate potential cyclic variations in serum SHBG levels during the normal menstrual cycle.
• To determine if SHBG changes are associated with fluctuations in key reproductive hormones, particularly estrogen.

Main Methods:

• Daily serum measurements of SHBG, luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol (E2), and progesterone were conducted over one menstrual cycle in 12 women.
• SHBG was quantified using both dextran-coated charcoal saturation analysis and radioimmunoassay (RIA).
• Hormone levels were measured using RIA, with LH also assessed via mouse Leydig cell bioassay.

Main Results:

• A significant increase in mean serum SHBG levels was observed during the luteal phase in 10 out of 12 women, following the preovulatory estradiol (E2) peak.
• Two women did not exhibit a significant SHBG increase; their luteal phase E2 levels were comparable to early follicular phase levels.
• In one of the non-responders, a minor SHBG rise was detected by RIA, indicating potential subtle hormonal interactions.

Conclusions:

• Serum SHBG levels demonstrably change during the menstrual cycle, closely associated with endogenous estradiol (E2) fluctuations.
• SHBG appears to serve as a reliable marker for tracking endogenous estrogen changes in normally ovulating women.
• The findings highlight the dynamic relationship between estrogen and SHBG within the context of the female reproductive cycle.