Growth hormone secretory dynamics over the menstrual cycle

Area of Science:

• Endocrinology
• Reproductive Physiology

Background:

• The relationship between the menstrual cycle and growth hormone (GH) secretion in women remains unclear.
• Previous studies have yielded conflicting results regarding estrogen's influence on GH during different cycle phases.

Purpose of the Study:

• To investigate whether GH secretion significantly varies across the early follicular (EF), periovulatory (PO), and luteal (L) phases of the menstrual cycle.
• To assess the impact of ovarian steroids on the GH axis, including GH secretion, IGF-I, and responses to TRH and GRH.

Main Methods:

• Collected 24-hour GH profiles via 10-minute sampling in 6 ovulatory women across EF, PO, and L phases.
• Measured TSH response to TRH, GH response to GRH, and fasting plasma IGF-I during each phase.
• Utilized deconvolution analysis to estimate GH secretion parameters.

Main Results:

• A non-significant trend towards higher integrated GH concentration (IGHC) was observed during the PO phase (p=0.09).
• Deconvolution analysis revealed no significant variation in GH secretion (p=0.56), pulse amplitude, or frequency across the cycle.
• Serum IGF-I levels remained constant, and TSH/GH responses to stimuli did not differ between phases. No correlations were found between IGHC and sex steroids.

Conclusions:

• The influence of fluctuating ovarian steroid levels on the GH axis during spontaneous menstrual cycles is minimal.
• Current findings suggest limited dynamic changes in GH secretion patterns throughout the menstrual cycle in healthy ovulatory women.