Increased expression of vascular endothelial growth/permeability factor in the rat ovary following an ovulatory gonadotropin stimulus: potential roles in follicle rupture.

Ovulation is accompanied by a large increase in the permeability of the capillaries surrounding the follicle, beginning a few hours after the ovulatory stimulus. The resulting edema may play a role in ovulation as well as in the formation and vascularization of the CL. Vascular endothelial growth/permeability factor (VEG/PF) is both a specific mitogen for endothelial cells and a potent stimulator of vascular permeability. The purpose of this study was to determine whether or not the ovulatory stimulus induces an increase in the expression of VEG/PF in the ovary. Female rats were primed with 8 IU of eCG at 27 days of age. Follicular maturation and ovulation were induced with an injection of hCG (5 IU) in the early afternoon on the second day after priming. Ovaries were removed 0, 1, 2, 4, 8, 10, and 18 h later. VEG/PF mRNA levels were compared through use of quantitative reverse transcription-polymerase chain reaction (RT-PCR). There was a marked increase (approximately 8-fold) in steady state levels of the transcripts for VEG/PF120 and VEG/PF164 between 1 and 4 h after hCG in whole ovaries. Increases were detectable both in granulosa cells and in thecal/stromal tissue. The high level of expression was maintained at 10 and 18 h (Day 1 CL). Thus, the preovulatory increase in follicular vascular permeability is closely associated with a marked, sustained increase in VEG/PF expression. VEG/PF, therefore, may play an important role in that increase and, consequently, in the process of ovulation as well as the subsequent vascularization of the CL.