Objectives: To evaluate the effects of endogenous estrogens and progestins on the IGF-system during the normal menstrual cycle in healthy premenopausal women not using contraceptive drugs.
Methods: Nine women had fasting blood samples obtained at 2-3 days intervals during a 5 week study period. Plasma levels of IGF-I, IGF-II, IGFBP-I, IGFBP-3, estradiol and progesterone were measured by radioimmunoassay (RIA) in each sample. IGFBP-3 was also evaluated by Western ligand blot (WLB) and immunoblot. Any differences between the menstrual phase (defined as day 1-5), follicular and luteal phases (separation based on plasma estradiol and progesterone values) were evaluated by the Friedman test.
Results: A small but significant difference in plasma levels of IGF-I (P < 0.01) and IGFBP-d (P < 0.05) measured by RIA between the three phases were seen with the highest levels found during the follicular phase. No change in plasma levels of IGFBP-1 and IGF-II was found and immunoblots did not reveal any alteration in the ratio of fragmented to intact IGFBP-3 during the menstrual cycle. A positive correlation between plasma levels of IGF-I and estradiol was seen in 8 out of 9 patients (P = 0.012).
Conclusions: The finding of a slight but significant higher level of plasma IGF-I in the follicular and luteal phases compared with the menstrual phase suggests plasma estradiol may influence the level of this growth factor. This hypothesis is further supported by the finding of a correlation between plasma levels of IGF-I and estradiol but not progesterone in individual patients at different times during the menstrual cycle.