Changes of messenger RNA expression of angiogenic factors and related receptors during follicular development in gilts

The interaction between angiogenic factors and related receptors is closely associated with follicular angiogenesis. The present study was performed to determine the relationships between the capillary network and mRNA expression of several angiogenic factors and related receptors during porcine follicular development. Ovaries in gilts were collected 72 h after eCG (1250 IU) treatment for histological observation. Granulosa cells and thecal tissues in small (diameter, <4 mm), medium (diameter, 4-5 mm), or large (diameter, >5 mm) individual follicles were collected for detection of mRNA expression of vascular endothelial growth factor (VEGF) 120, VEGF 164, basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF) in granulosa cells and fms-like tyrosine kinase (Flt-1), fetal liver kinase (Flk-1) or the murine homologue of kinase domain region (KDR), bFGF receptor (bFGF-R), and EGF receptor (EGF-R) in thecal tissue by semiquantitative reverse transcription-polymerase chain reaction. The eCG treatment resulted in the emergence of healthy preovulatory follicles (diameter, >6.0 mm) that possessed more capillaries in the thecal cell layer and a significant increase in the percentage of atretic follicles of 1.0-2.9 mm in diameter. The number of capillaries in the thecal cell layer increased significantly in healthy follicles larger than 3 mm in diameter in the eCG group compared with those in controls. The expression of VEGF 120, VEGF 164, and bFGF mRNAs increased in granulosa cells of medium and large follicles from ovaries of prepubertal gilts after eCG treatment. The Flt-1, Flk1/KDR, and bFGF-R mRNA expression increased in theca cells of medium and large follicles after eCG treatment. The expression of EGF mRNA increased in granulosa cells of small, medium, and large follicles from ovaries after eCG treatment, but the mRNA expression of EGF-R in thecal tissue did not change. These data indicate that preovulatory follicles possessed a larger capillary network and expressed more mRNAs of angiogenic factors in granulosa cells and related receptors in thecal tissue. We concluded that VEGF 120, VEGF 164, bFGF, and EGF may be greatly involved in the angiogenic process of follicular development in prepubertal gilts with eCG treatment.