Insulin-like growth factor-1, a component of serum that enables porcine cumulus cells to expand in response to follicle-stimulating hormone in vitro.
The present study was aimed at determining whether insulin-like growth factor-1 (IGF-1) is a component of fetal bovine serum (FBS) that enables porcine cumulus cells to expand in response to FSH in vitro. Cumulus-oocyte complexes (COC) obtained from 4- to 6-mm follicles of prepubertal gilts were cultured at 39 degrees C for 24 h in media that contained human recombinant IGF-1 (50 ng/ml), FBS (15% v:v), or their combination, with or without FSH (1.5 microg/ml), and cumulus expansion was scored microscopically. Expansion was FSH dependent and was observed only when IGF-1, FBS, or both were present. The proportion of FSH-stimulated COC exhibiting full expansion in response to IGF-1 alone did not differ significantly (p > 0.05) from the proportion in those cultured with FBS or IGF-1+FBS (79 +/- 2.8% vs. 84 +/- 2.2% or 76 +/- 6.2%, respectively). In a concentration-response study, FSH-stimulated expansion was observed in a significant proportion of COC (32 +/- 2.8% vs. 0% control) at 1 ng/ml IGF-1, with the proportions increasing dose-dependently to maximal values between 10 and 75 ng/ml IGF-1, and decreasing at higher IGF-1 concentrations. Exposure of COC to an IGF-1 receptor (IGF-1R)-neutralizing antibody (Ab) for 90 min before addition of FSH and FBS dose-dependently inhibited cumulus expansion, with maximal inhibition at 10 microg/ml (1 +/- 1.0% vs. 68 +/- 1.1% control). In the absence of FBS or IGF-1, some COC had a tendency toward slight expansion when cultured with FSH, and the Ab completely inhibited that effect, suggesting that this may be due to endogenous IGF-1 production by the COC. The Ab effect was reversible and was eliminated by washing twice with fresh medium followed by culture for an additional 24 h in the presence of FSH and FBS. Expression of IGF-1R mRNA in the isolated oocyte and cumulus cells was determined by reverse tramscriptase polymerase chain reaction using sequence-specific primers. The IGF-1R message was detected in both the oocyte and cumulus cells. Collectively, these observations suggest that IGF-1 is a component of serum that enables cumulus cells to expand in response to FSH in vitro, and that the effect is receptor mediated. Since IGF-1 is present in the follicle in vivo, it may have a physiological role during gonadotropin-induced cumulus expansion.
Singh
B
B
Department of Obstetrics and Gynaecology, The University of Western Ontario, London, Canada.
Armstrong
D T
DT
D000818:Animals; D001483:Base Sequence; D002417:Cattle; D003470:Culture Media; D017931:DNA Primers / Q000235:genetics; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D009865:Oocytes / Q000378:metabolism; D006080:Ovarian Follicle / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D013552:Swine
D003470:Culture Media; D017931:DNA Primers; D012333:RNA, Messenger; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone