Remarkable changes in vascular permeability and neovascularization occur within the ovulatory, luteinizing follicle. To evaluate the importance of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) in periovulatory events, sequential experiments were designed in which vehicle (PBS/0.1% BSA; controls, n = 13) or a low dose (1.5 μg; n = 4) or a high dose (7.5 μg; n = 4) of a VEGF antagonist, soluble VEGF receptor 1 (sVEGFR1) chimera, was injected directly into the preovulatory follicle of rhesus monkeys the day before (Day −1) or the day of (Day 0) the midcycle LH surge during spontaneous menstrual cycles. After vehicle injection, animals typically exhibited patterns and levels of serum progesterone (P4) that were comparable to those of untreated animals in our colony. Following low-dose sVEGFR1 injection, serum P4 levels were diminished in two of four animals from the early to midluteal phase, but were similar to vehicle controls thereafter. In contrast, high-dose sVEGFR1 injection decreased serum P4 levels throughout the luteal phase compared with levels in controls (P < 0.05), but it did not cause premature menstruation. Control follicles displayed indices of rupture (protruding stigmata) and luteinization. However, sVEGFR1-injected follicles exhibited signs of distension (torn surface epithelium/tunica albuginea) and luteinization, but not necessarily timely ovulation. Histological evaluation of serial sections from ovaries removed on Day 3 after treatment revealed that all (n = 3) vehicle-injected follicles ovulated, whereas half (n = 3 of 6) the sVEGFR1-injected follicles failed to ovulate and still contained an oocyte in the antrum. No appreciable differences were apparent between treatment groups in numbers of cells in luteal tissue (Day 3 or 6 after treatment) that stained positive for immunochemical or histochemical markers of proliferative (Ki67), endothelial (platelet endothelial cell adhesion molecule 1), and steroidogenic (3β-hydroxysteroid dehydrogenase) cells. However, there was a dose-dependent increase (P < 0.05) in extracellular space in the corpus luteum by midluteal phase in sVEGFR1-treated animals. The data suggest that acute exposure to a VEGF antagonist can impair ovulation, and the subsequent development and functional capacity of the primate corpus luteum. The results are consistent with a critical role for VEGF in normal ovarian function during the periovulatory interval in primates.
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