Endocrine Abstracts

The role of the intra-ovarian insulin-like growth factor (IGF) system in preantral follicle development is unclear. Here we have examined the expression of mRNA for insulin-like growth factor-1 (IGF-1), IGF-2, Type 1-IGF receptor, Type 2-IGF receptor and insulin receptor (IR) in human pre-antral follicles at different stages. Ovarian cortex biopsies (5mm³) were obtained (with informed consent) during gynaecological surgery from six women (age 32.2 plus/minus SD 2.2, range 22 to 39 years ). Follicles (n=53) were enzymatically and mechanically isolated, measured and the stage of follicular development determined. Individual follicles were lysed to release mRNA, reverse transcribed, then subjected to a nested PCR protocol using primers specifically designed for each of the ligands and receptors listed above. cDNA from whole ovarian cortical tissue was used as a positive control. Expression of beta-actin was used to confirm the presence of cDNA prepared from each oocyte and follicle (n=45 out of 53).

Type 1-IGFR mRNA was detected in 17 out of 31 follicles from different stages i.e oocytes (n=1/2), primordial (n=3/5), transitional (n=5/9), primary (n=5/9), secondary (n=1/4) and preantral (n=2/2). IGF-2 ligand was also detectable in some but not all of the same follicles (10/31) i.e.oocytes (n=2/2), primordial (n=1/5), transitional (n=4/9), primary (n=2/9), secondary (n=0/4) and preantral (n=1/2). We were unable to detect mRNA expression of IGF-1, IR or Type 2-IGFR in any of the oocytes or follicles at any stage of pre-antral development. To conclude, IGF-2 appears to be the only ligand that is endogenously expressed by human pre-antral follicles, which could act in an autocrine manner through the Type-1 IGF receptor. However this does not exclude an endocrine role for IGF-1 on human pre-antral follicles.