CHANGES IN SERUM CONCENTRATIONS OF GROWTH-HORMONE, INSULIN, INSULIN-LIKE-GROWTH-FACTOR AND INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-1 ANDPROTEIN-3 AND URINARY GROWTH-HORMONE EXCRETION DURING THE MENSTRUAL-CYCLE

Few studies exist on the physiological changes in the concentrations o f growth hormone (GH), insulin-like growth factors (IGF) and ICE-bindi ng proteins (IGFBP) within the menstrual cycle, and some controversy r emains. We therefore decided to study the impact of endogenous sex ste roids on the GH-IGF-IGFBP axis during the ovulatory menstrual cycle in 10 healthy women (aged 18-40 years). Blood sampling and urinary colle ction was performed every morning at 0800 h for 32 consecutive days. E very second day the subjects were fasted overnight before blood sampli ng. Follicle stimulating hormone, luteinizing hormone (LH), oestradiol , progesterone, IGF-I, 1GFBP-3, sex hormone-binding globulin, dihydroe piandrosterone 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 p roliferative phase (P < 0.001). Mean individual variation in IGF-I con centrations 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 1GFBP-3 concentrations between the luteal and t he proliferative phases. Mean individual variation in IGFBP-3 concentr ations throughout the menstrual cycle was 8.8% (SD 2.7; range 3.2-14.1 ). IGFBP-1 concentrations were inversely associated with insulin conce ntrations, and showed a significant pre-ovulatory increase that return ed to baseline at the day of the LH surge. Easting insulin concentrati ons showed large fluctuations throughout the menstrual cycle without a ny distinct cyclic pattern. No cyclic changes in urinary GH excretion during menstrual cycle were detected. We conclude that, although ICE-I concentrations are dependent on the phase of the menstrual cycle, the variation in IGF-I concentrations throughout the menstrual cycle is r elatively small. Therefore, the menstrual cycle does not need to be co nsidered when evaluating IGF-I or 1GFBP-3 serum values in women suspec ted to have GH deficiency.