Immunoreactive insulin-like growth factor I in human follicular fluid

Recent studies in laboratory animals suggest that insulin-likegrowth factor I (IGF-I) plays an important role in the regulationof granulosa cell function. The purpose of the present studywas to investigate the presence of immunoreactive IGF-I in humanfollicular fluid (FF) and compare the levels of follicular IGF-I(64 follicles) with those detectable in serum (n= 19) in hyperstimulatedcycles from 25 infertile patients. Also, the FF IGF-I levelswere correlated to corresponding follicular volume (n= 62) andoocyte maturation (n= 37). Levels of IGF-I were determined usinga specific radioimmunoassay after acidification and extractionby reversed phase chromatography. Levels of IGF-I in serum weresignificantly higher than those in FF (37.1± 10.1 versus24.0± 9.3 nmol/I, n= 19, P< 0.001). A positive correlationwas found between follicular and serum IGF-I concentrations(r= 0.73). No significant differences were found in FF IGF-Ilevels derived from follicles of different size or from follicleshaving oocytes with different grades of maturation. These dataindicate that immunoreactive IGF-I is present in human FF innanomolar concentrations and that FF IGF-I levels correlatewith those detectable in serum. The source of FF IGF-I and itsregulatory role in humans remains to be elucidated.