Changes of mRNA expression of vascular endothelial growth factor, angiopoietins and their receptors during the periovulatory period in eCG/hCG-treated immature female rats.

Angiogenic factors can induce the perifollicular capillary network in the theca interna that shows marked changes in and around the preovulatory luteinizing hormone (LH) surge. To get more information on their functional crosstalk, the aim of the present study was to investigate the manner of mRNA expression of vascular endothelial growth factors (VEGFs) 120, 164, angiopoietin (Ang)-1, Ang-2 and their specific receptors during the periovulatory phase. We used an established equine and human chorionic gonadotropins (eCG/hCG)-derived experimental model capable of stimulating naturally occurring follicular maturation, ovulation and corpus luteum (CL) formation. On day 28 postpartum, immature female rats were administrated s.c. with 10 IU of eCG to promote follicular development, followed 48 hr later by i.p. administration of 20 IU of hCG. Ovaries were dissected at 0, 6, 12, 18 and 24 hr after hCG treatment, and were obtained on day 30 in the untreated control. After induction of follicular growth by the eCG treatment, each mRNA expression of VEGF 120, VEGF 164, Neuropilin-1 and Flt-1 significantly increased. The peaks in mRNA expressions of VEGF120 and VEGF164 were both found at 18 hr after hCG treatment. Flk-1 mRNA expression maintained up to 6 hr after hCG treatment, and then decreased at 12, 18 and 24 hr after hCG treatment. Ang-2 mRNA expression increased in the ovaries at 6 and 12 hr after hCG treatment. Tie-2 mRNA expression decreased at 24 hr after the treatment of gonadotropins. Our findings suggest that ovarian vascular formation during the periovulatory period including preovulatory follicles, ovulation and CL formation may develop via crosstalk of the VEGF-Flt-1 and Ang-Tie2 systems.