Immunoreactive insulin-like growth factor I in human follicular fluid

Recent studies in laboratory animals suggest that insulin-like growth factor I (IGF-I) plays an important role in the regulation of granulosa cell function. The purpose of the present study was to investigate the presence of immunoreactive IGF-I in human follicular fluid (FF) and compare the levels of follicular IGF-I (64 follicles) with those detectable in serum (n = 19) in hyperstimulated cycles from 25 infertile patients. Also, the FF IGF-I levels were correlated to corresponding follicular volume (n = 62) and oocyte maturation (n = 37). Levels of IGF-I were determined using a specific radioimmunoassay after acidification and extraction by reversed phase chromatography. Levels of IGF-I in serum were significantly higher than those in FF (37.1 +/- 10.1 versus 24.0 +/- 9.3 nmol/l, n = 19, P less than 0.001). A positive correlation was found between follicular and serum IGF-I concentrations (r = 0.73). No significant differences were found in FF IGF-I levels derived from follicles of different size or from follicles having oocytes with different grades of maturation. These data indicate that immunoreactive IGF-I is present in human FF in nanomolar concentrations and that FF IGF-I levels correlate with those detectable in serum. The source of FF IGF-I and its regulatory role in humans remains to be elucidated.