Expression of vascular endothelial growth factor in rat ovary during pregnancy and postpartum

The expressions of vascular endothelial growth factor (VEGF) in rat ovarian follicles and corpus luteum (CL) during different stages of pregnancy and postpartum were investigated. In addition, the effect of tumor necrosis factor-alpha (TNF-alpha) on VEGF expression was examined. VEGF mRNA was localized in granulosa cells of preantral follicles, as well as in the granulosa and theca cells of small antral follicles, but not in large antral follicles. VEGF transcripts were amplified in rat CL during pregnancy and postpartum using RT-PCR. The mRNA expression reached the maximal level on day 7, maintained it on days 9-18, decreased after day 18, and was minimal on day 1 postpartum. Western blot showed a 23 ku VEGF protein band in rat CL. Expression of VEGF protein varied in a similar way to that of its mRNA. Treatment with TNF-alpha at a dosage of 3000 IU/kg on day 4 of pregnancy significantly increased VEGF expression in rat CL. It is suggested that the down-regulation of VEGF expression in large antral follicles may be one factor that contributes to the termination of ovulation in rat ovary during pregnancy. VEGF may be implicated in the CL formation and maintenance via regulating angiogenesis, and its expression is regulated by TNF-alpha.