ALTERATIONS IN THE INSULIN-LIKE-GROWTH-FACTOR SYSTEM DURING THE MENSTRUAL-CYCLE IN NORMAL WOMEN

Objectives: To evaluate the effects of endogenous estrogens and proges tins on the IGF-system during the normal menstrual cycle in healthy pr emenopausal women not using contraceptive drugs. Methods: Nine women h ad fasting blood samples obtained at 2-3 days intervals during a 5 wee k study period. Plasma levels of IGF-I, IGF-II, IGFBP-1, IGFBP-3, estr adiol and progesterone were measured by radioimmunoassay (RIA) in each sample. IGFBP-3 was also evaluated by Western ligand blot (WLB) and i mmunoblot. Any differences between the menstrual phase (defined as day 1-5), follicular and luteal phases (separation based on plasma estrad iol and progesterone values) were evaluated by the Friedman test. Resu lts: A small but significant difference in plasma levels of IGF-I (P < 0.01) and IGFBP-3 (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 immunob lots did not reveal any alteration in the ratio of fragmented to intac t IGFBP-3 during the menstrual cycle. A positive correlation between p lasma 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 wi th the menstrual phase suggests plasma estradiol may influence the lev el 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. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.