MENSTRUAL CYCLE-ASSOCIATED CHANGES IN BLOOD-LEVELS OF INTERLEUKIN-6, ALPHA-1-ACID GLYCOPROTEIN, AND C-REACTIVE PROTEIN

Based on previous studies we hypothesized that interleukin-6 (IL-6) pl asma levels would increase during the menstrual cycle, in analogy to t he increase in IL-1 levels seen during the luteal phase. Thus we have investigated menstrual cycle-associated changes in IL-6, alpha 1 acid glycoprotein (AGP), and C-reactive protein (CRP). The study design was cross-sectional and was conducted in 18 healthy premenopausal women w ith regular menstrual cycles and in 15 age-matched men. The women had blood drawings in the follicular phase, at midcycle, and in the luteal phase of the menstrual cycle. A single blood sample was obtained from men to compare IL-6 levels between sexes. The median IL-6 level was 0 .68 pg/ml (95% confidence interval (CI): 0.60 to 1.05) in the follicul ar phase and did not change significantly during the menstrual cycle. IL-6 levels did not differ between women and men (0.79 pg/ml; CI: 0.66 to 1.05; p > 0.05). Median AGP levels decreased by 6% (CI: -14% to 1% ) during the luteal phase (p = 0.005), and a significant correlation b etween mean AGP and IL-6 levels was found (r = 0.60; p = 0.01). Median CRP levels increased by 44% (CI: 27% to 59%; p < 0.001) at midcycle a nd by 31% (CI: 17% to 68%; p = 0.002) in the luteal phase, and there w as a significant correlation between the relative increase in CRP at m idcycle and the relative increase in progesterone levels during midcyc le (r = 0.60; p = 0.01) and the luteal phase (r = 0.71; p = 0.001), In conclusion, we found no sustained menstrual cycle-dependent changes i n systemic IL-6 plasma levels. AGP and CRP levels may be differentiall y regulated during the menstrual cycle of healthy women: AGP levels co rrelated with IL-6 levels, and AGP levels decreased during the menstru al cycle, whereas CRP levels increased during the menstrual cycle and correlated with the increase in progesterone levels. The reason for th e observed changes in CRP levels remains to be elucidated.