Changes in serum concentrations of growth hormone, insulin, insulin-like growth factor and insulin-like growth factor-binding proteins 1 and 3 and urinary growth hormone excretion during the menstrual cycle.

Few studies exist on the physiological changes in the concentrations of growth hormone (GH), insulin-like growth factors (IGF) and IGF-binding proteins (IGFBP) within the menstrual cycle, and some controversy remains. We therefore decided to study the impact of endogenous sex steroids on the GH-IGF-IGFBP axis during the ovulatory menstrual cycle in 10 healthy women (aged 18-40 years). Blood sampling and urinary collection was performed every morning at 0800 h for 32 consecutive days. Every second day the subjects were fasted overnight before blood sampling. Follicle stimulating hormone, luteinizing hormone (LH), oestradiol, progesterone, IGF-I, IGFBP-3, sex hormone-binding globulin, dihydroepiandrosterone sulphate and GH were determined in all samples, whereas insulin and IGFBP-1 were determined in fasted samples only. Serum IGF-I concentrations showed some fluctuation during the menstrual cycle, with significantly higher values in the luteal phase compared to the proliferative phase (P < 0.001). Mean individual variation in IGF-I concentrations throughout the menstrual cycle was 13.2% (SD 4.3; range 0.1-18.3%). There were no cyclic changes in IGFBP-3 serum concentrations and no differences in IGFBP-3 concentrations between the luteal and the proliferative phases. Mean individual variation in IGFBP-3 concentrations throughout the menstrual cycle was 8.8% (SD 2.7; range 3.2-14.1). IGFBP-1 concentrations were inversely associated with insulin concentrations, and showed a significant pre-ovulatory increase that returned to baseline at the day of the LH surge. Fasting insulin concentrations showed large fluctuations throughout the menstrual cycle without any distinct cyclic pattern. No cyclic changes in urinary GH excretion during menstrual cycle were detected. We conclude that, although IGF-I concentrations are dependent on the phase of the menstrual cycle, the variation in IGF-I concentrations throughout the menstrual cycle is relatively small. Therefore, the menstrual cycle does not need to be considered when evaluating IGF-I or IGFBP-3 serum values in women suspected to have GH deficiency.