Follicular fluid levels of insulin-like growth factor I, insulin-like growth factor binding protein I, and ovarian steroids collected during ovum pick-up

Objective: To evaluate interrelationships between levels of insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein (IGFBP- I), and ovarian steroids in late preovulatory follicular fluid (FF) after pituitary desensitization with GnRH agonist and controlled ovarian hyperstimulation. Design: Follicular fluid and matched serum were collected during the ovum pick-up. Insulin-like growth factor binding protein I, E₂, P, and androstenedione (A) were measured by means of RIA, whereas T was measured by means of fluoroimmunoassay and IGF-I by means of immunoradiometric assay. Setting: University teaching hospital. Participants: Fifty-nine patients underwent 62 ovum pick-ups for IVF. Main Outcome Measures: Levels of IGF-I, IGFBP-I, E₂, P₄ (representative of follicular maturity), T, and A in FF and the volume of this fluid were determined. Levels of E₂ to A (representative of aromatase activity) in FF were examined in relation to the volume of FF. Results: Levels of FF-IGF-I decreased with increasing volume of FF. This observation is unprecedented. In contrast, FF- P increased with increasing volume of FF. The reverse relationships with FF volume between FF-IGF-I and FF-P may not be causal because no correlation was found between concentrations of FF-IGF-I and FF-P. Our findings are consistent with and complementary to those in previous reports. The follicular fluid E₂:A ratio, FF-E₂, FF-A, FF-T, and FF-IGFBP-I were not found to be correlated with volume of FF. Conclusion: Decreased levels of FF- IGF-I with unaltered levels of FF-IGFBP-I in larger follicles may favor a shift toward diminished action of IGF-I at the time of immediate preovulation. The physiological significance of this shift remains uncertain as it is not reflected in the levels of steroids in FF.