The gene for KDR (kinase insert domain receptor), a growth factor receptor tyrosine kinase, was cloned from a human endothelial cell cDNA library Terman et al., 1991. The predicted amino acid sequence contained multiple characteristics (e.g., an ATP binding site, a membrane spanning region, split tyrosine kinase regions) typical of known type III receptor tyrosine kinases (e.g., platelet-derived growth factor receptor), colony stimulating factor-1 receptor), fibroblast growth factor receptor), and KIT).
Flk1 is the mouse homolog of KDR Matthews et al., 1991. KDR and its mouse homolog bind vascular endothelial growth factor with high affinity in vitro and are expressed early in development by endothelial cell precursors.
NCBI Summary:
Vascular endothelial growth factor (VEGF) is a major growth factor for endothelial cells. This gene encodes one of the two receptors of the VEGF. This receptor, known as kinase insert domain receptor, is a type III receptor tyrosine kinase. It functions as the main mediator of VEGF-induced endothelial proliferation, survival, migration, tubular morphogenesis and sprouting. The signalling and trafficking of this receptor are regulated by multiple factors, including Rab GTPase, P2Y purine nucleotide receptor, integrin alphaVbeta3, T-cell protein tyrosine phosphatase, etc.. Mutations of this gene are implicated in infantile capillary hemangiomas. [provided by RefSeq, May 2009]
General function
Receptor, Anti-apoptotic, Enzyme, Transferase
Comment
The VEGF/VEGF Receptor 2 Pathway is Critical for Blood Vessel Survival in Corpora Lutea of Pregnancy in the Rodent.
Pauli SA, et al .
The VEGF/VEGF receptor 2 (VEGFR-2) pathway regulates proliferation, survival and permeability of vasculature. This pathway is active during the formation of a corpus luteum, a highly vascularized, endocrine organ with a short life span during the non-pregnant state. In the pregnant state, life span of corpora lutea is much longer as they play a critical role in supporting pregnancy development. We hypothesized that the VEGF/VEGFR-2 pathway plays a critical role in regulating angiogenic events in corpora lutea of pregnancy. Injection of the neutralizing anti-VEGFR-2 antibody DC101 (ImClone Systems Inc., NY, NY) on embryonic day 3.5 (pre-implantation) or 6.5 (post-implantation) disrupts function of corpora lutea of pregnancy in CD1 mice as evidenced by a decrease in organ size, regression of luteal vessels, and a fall in progesterone secretion within 24 h post injection. Inhibition of the VEGFR-2 receptor caused removal of endothelial cells mostly through endothelial cell detachment from the vascular basement membrane. Luteal steroid producing epithelial cells were eliminated through apoptosis secondary to vasculature becoming dysfunctional. Disruption of luteal function caused arrest of embryonic development. The effect of antibody is specific to the ovary as pregnancy progresses normally in ovariectomized, progesterone replaced animals treated with anti-VEGFR-2 antibody. Embryonic blood vessels were not affected directly by the antibody as it did not reach the embryo. Administration of an antibody against VE-cadherin (E4G10; ImClone Systems Inc., NY, NY), which specifically blocks endothelial proliferation, did not disrupt luteal function and pregnancy development. Thus, VEGFR-2 mediated endothelial cell signals are critical to maintain functionality of luteal blood vessels during pregnancy. Potential clinical applications of inhibitors of the VEGF/VEGFR-2 pathway include emergency contraception, medical treatment of ectopic and abnormal intrauterine pregnancies.
Single Injections of Vascular Endothelial Growth Factor Trap Block Ovulation in the Macaque and Produce a Prolonged, Dose-Related Suppression of Ovarian Function Fraser HM, et al .
Follicular development is associated with intense angiogenesis and increased permeability of blood vessels under the control of locally-produced angiogenic factors such as vascular endothelial growth factor (VEGF). The aim of the present study was to evaluate the effects of transient inhibition of VEGF on pituitary-ovarian function in the macaque. Animals were given a single, intravenous injection of a potent, receptor-based VEGF antagonist, the VEGF Trap. VEGF Trap was given at a dose of 4, 1 or 0.25 mg/kg in the mid-follicular phase or at 1.0 mg/kg in the late follicular phase. Controls were treated with vehicle or a control protein, recombinant human Fc (1 mg/kg). Blood samples were collected once daily for 12 days following injection, and three times per week thereafter until normal ovulatory cycles had resumed. The VEGF Trap produced a rapid suppression of estradiol and inhibin B concentrations at all doses tested, followed by a marked and sustained increase in LH and FSH. Ovulation and formation of a functional corpus luteum, as evidenced by increased serum progesterone levels, failed to occur at the anticipated time. Normal ovarian activity resumed when plasma concentrations of unbound VEGF Trap fell below about 1 mg/L. When treatment was initiated in the mid-follicular phase, control macaques ovulated 7.2 +/- 0.4 days later, but ovulation was delayed in a dose dependent manner by VEGF Trap, occurring 23 +/- 0.7, 30 +/- 1.4 and 43 +/- 0.8 days after injection of 0.25, 1 or 4 mg/kg respectively. Thus, the VEGF Trap exerts a potent, dose-dependent but reversible inhibitory effect on ovarian function.
Prostaglandin E2 and vascular endothelial growth factor A mediate angiogenesis of human ovarian follicular endothelial cells. Trau HA et al. (2016) Which receptors for prostaglandin E2 (PGE2) and vascular endothelial growth factor A (VEGFA) mediate angiogenesis in the human follicle around the time of ovulation? PGE2 and VEGFA act via multiple PGE2 receptors (PTGERs) and VEGF receptors (VEGFRs) to play complementary roles in follicular angiogenesis. Production of PGE2 and VEGFA by the follicle are prerequisites for ovulation. PGE2 is an emerging regulator of angiogenesis and has not been examined in the context of the human ovulatory follicle. VEGFA is an established regulator of follicular angiogenesis. Ovarian biopsies containing the ovulatory follicle were obtained from 11 women of reproductive age (30-45 years) undergoing surgery for laparoscopic sterilization. In some cases, women received hCG to substitute for the ovulatory LH surge before ovarian biopsy. In addition, aspirates from four women of reproductive age (18-31 years) undergoing gonadotrophin stimulation for oocyte donation were obtained for isolation of human ovarian microvascular endothelial cells (hOMECs). Ovarian biopsies were utilized for immunocytochemical detection of von Willebrand factor to identify endothelial cells. hOMECs were cultured with PGE2, PTGER receptor selective agonists, VEGFA, or VEGFR selective agonists. hOMECs were assessed for proliferation by Ki67 immunocytochemistry. hOMEC migration was determined by counting cells which migrated through a porous membrane in vitro. Sprout formation was quantified by determining sprout number and length from photographs take after culture of hOMECs in a 3-dimensional matrix. Endothelial cells were not observed within the granulosa cell layer of human ovulatory follicles prior to an ovulatory dose of hCG and were first seen amongst granulosa cells 18-34 h after hCG. In vitro, PGE2 enhanced migration and sprout formation but did not alter hOMEC proliferation. Agonists selective for each PTGER increased migration with no change in proliferation. PTGER1 and PTGER2 agonists increased the number of sprouts, while only PTGER1 affected sprout length. VEGFA increased hOMEC proliferation, migration, and formation of structures resembling capillary sprouts. Signaling through VEGFR1 promoted hOMEC migration, proliferation, and the formation of few, long endothelial cell sprouts, while VEGFR2 stimulation promoted hOMEC migration and the formation of many, short sprouts. All effects of treatments in vitro were considered significant at P < 0.05. While primary cultures of hOMECs respond to PGE2 and VEGFA differently than other cultured endothelial cells, hOMECs may not respond to PGE2 and VEGFA in vivo as they do in vitro. Agonists and antagonists selective for PTGER1, PTGER2, VEGFR1, or VEGFR2 may have therapeutic value to promote or prevent ovulation in women. This research was supported by grant funding from the Eunice Kennedy Shriver National Institutes of Child Health and Human Development (HD071875 to D.M.D., T.E.C., M.B.). The authors have no conflicts of interest to disclose.//////////////////
The luteotrophic function of galectin-1 by binding to the glycans on vascular endothelial growth factor receptor-2 in bovine luteal cells. Sano M et al. (2015) The corpus luteum (CL) is a temporary endocrine gland producing a large amount of progesterone, which is essential for the establishment and maintenance of pregnancy. Galectin-1 is a β-galactose-binding protein that can modify functions of membrane glycoproteins and is expressed in the CL of mice and women. However, the physiological role of galectin-1 in the CL is unclear. In the present study, we investigated the expression and localization of galectin-1 in the bovine CL and the effect of galectin-1 on cultured luteal steroidogenic cells (LSCs) with special reference to its binding to the glycans on vascular endothelial growth factor receptor-2 (VEGFR-2). Galectin-1 protein was highly expressed at the mid and late luteal stages in the membrane fraction of bovine CL tissue and was localized to the surface of LSCs in a carbohydrate-dependent manner. Galectin-1 increased the viability in cultured LSCs. However, the viability of LSCs was decreased by addition of β-lactose, a competitive carbohydrate inhibitor of galectin-1 binding activity. VEGFR-2 protein, like galectin-1, is also highly expressed in the mid CL, and it was modified by multi-antennary glycans, which can be recognized by galectin-1. An overlay assay using biotinylated galectin-1 revealed that galectin-1 directly binds to asparagine-linked glycans (N-glycans) on VEGFR-2. Enhancement of LSC viability by galectin-1 was suppressed by a selective inhibitor of VEGFR-2. The overall findings suggest that galectin-1 plays a role as a survival factor in the bovine CL, possibly by binding to N-glycans on VEGFR-2.//////////////////
Inhibition of Vascular Endothelial Growth Factor Receptor Signal Transduction Blocks Follicle Progression but Does Not Necessarily Disrupt Vascular Development in Perinatal Rat Ovaries. McFee RM et al. We hypothesized that VEGFA angiogenic isoforms and their receptors, FLT1 and KDR, regulate follicular progression in the perinatal rat ovary. Each VEGFA angiogenic isoform has unique functions, based on their exons, which affects diffusibility, cell migration, branching, and development of large vessels. The Vegfa angiogenic isoforms (120, 164, 188) were detected in developing rat ovaries and quantitative RT-PCR determined Vegfa_120 and 164 mRNA was more abundant after birth while Vegfa_188 mRNA was highest at Embryonic Day 16. VEGFA and its receptors were localized to pre-granulosa and granulosa cells of all follicle stages and to theca cells of advanced stage follicles. To determine the role of VEGFA in developing ovaries, Postnatal Day 3/4 rat ovaries were cultured with 8 microM of VEGFR-TKI, a tyrosine kinase inhibitor that blocks FLT1 and KDR. Ovaries treated with VEGFR-TKI had vascular development reduced by 94% (P < 0.0001) with more primordial follicles (stage 0), fewer early primary, transitional, and secondary follicles (stages 1, 3, and 4, respectively), and greater total follicle numbers compared to control ovaries (P < 0.005). V1, an inhibitor specific for KDR, was utilized to determine the effects of only KDR inhibition. Treatment with 30 microM of V1 had no effect on vascular density; however, treated ovaries had fewer early primary, transitional, and secondary follicles and more primary follicles (stage 2) compared to control ovaries (P < 0.05). We conclude that VEGFA may be involved in primordial follicle activation and follicle maturation/survival which are regulated through both vascular dependent and independent mechanisms.
Sugino N, et al 2000 reported the expression of vascular endothelial growth factor and its
receptors in the human corpus luteum during the menstrual cycle
and in early pregnancy.
Messenger RNA (mRNA)
expression of VEGF, flt-1, and KDR remained constant in the CL during the
luteal phase and was lower in the regression phase. In the pregnant CL, VEGF
mRNA expression was higher compared with that in the midluteal phase, and mRNA
expression of both flt-1 and KDR was the same as that in the midluteal phase.
Western blot analyses revealed that the change in protein expression of VEGF,
flt-1, and KDR was similar to that in their mRNA expression. To study the
effect of human CG (hCG) on VEGF expression in the CL, corpora lutea obtained
from the midluteal phase were incubated with hCG (1 IU/ml) for 6 h. hCG
increased the expression of mRNA and protein of VEGF.
Gene whose expression is detected by cDNA array hybridization: transporters, signal transduction. Also, relative transcript level reproducibly decreases during IVM Rozenn Dalbi?Tran and Pascal Mermilloda
Neutralization of Endogenous Vascular Endothelial Growth Factor Depletes Primordial Follicles in the Mouse Ovary. Roberts AE et al. The regulation of early follicular growth and development involves a complex interaction of autocrine, paracrine, and endocrine signals. The ability of these factors to regulate follicle growth may depend, in part, on the extent of vascular delivery to and perfusion of the ovary. Vascular endothelial growth factor A (VEGFA) is a major regulator of vascular physiology in the ovary. VEGFA is produced in numerous ovarian compartments, and likely plays a role in the regulation of all phases of follicular growth from preantral through preovulatory. The aim of the present study was to further evaluate the role of VEGF in early follicle growth by neutralization of endogenous VEGF or VEGF receptors. Adult mice were injected systemically or prepubertal mice were injected directly under the ovarian bursa with antibodies designed to neutralize VEGF or block interaction with its receptors in the ovary. Both systemic and intrabursal injections of VEGF antibody significantly reduced the number of primordial follicles within 1-3 days after administration without affecting primary or secondary follicle numbers. Primordial follicle numbers were not different from control levels by 30 days after VEGFA antibody administration. Administration of antibodies to the kinase domain receptor (KDR) for VEGF but not the FMS-like tyrosine receptor (FLT1) for VEGF also results in a significant decrease in primordial follicles. These data suggest that VEGF plays a vital role in the maintenance and growth of the primordial follicle pool.
Expression regulated by
Steroids, Growth Factors/ cytokines
Comment
Vascular endothelial growth factor-induced expression of its receptors and activation of the MAPK signaling pathway during ovine oocyte maturation in vitro. Yan L et al. The vascular endothelial growth factor (VEGF) has beneficial effects on ovine oocytes during in vitro maturation and their subsequent early embryonic development, but the biochemical pathway underlying this effect has not been elucidated. Therefore, the focus of the present study was to investigate the activation of the mitogen-activated protein kinase (MAPK) pathway in response to the addition of VEGF to the maturation medium, and to study the subcellular localization of VEGF and its receptors during ovine oocyte maturation. We concluded that: (1) VEGF mainly localized in the cytoplasm, whereas its receptors, fms-tyrosine kinase-1 and kinase domain region (KDR), were localized on the plasma membrane of oocytes; (2) the addition of 5 ng/mL VEGF increased the percentage of oocytes with extruded first polar bodies (50.9 ? 2.2% vs. 34.6 ? 2.9%; treatment vs. control, respectively; P < 0.01) and the rate of oocytes competent to undergo nuclear maturation (70.6 ? 0.9% vs. 62.9 ? 1.9%, P < 0.01); and (3) as the expression of VEGF, fms-tyrosine kinase-1, and KDR increased after supplementation with 5 ng/mL, expression of VEGF, mitogen-activated protein kinase kinase (MEK), and MAPK mRNA, as well as MAPK phosphorylation, were stimulated in a time-dependent manner. We inferred that, in a paracrine manner, exogenous VEGF bound to KDR, its main receptor, and then activated the MAPK signaling pathway, which promoted maturation of ovine oocytes. However, the VEGF system also had an autocrine regulatory loop that contributed to creating an environment optimal for oocyte maturation.
Progesterone induces the expression of vascular endothelial growth factor (VEGF) 120 and Flk-1, its receptor, in bovine granulosa cells. Shimizu T et al. Vascular endothelial growth factor (VEGF) isoforms (VEGF 120 and VEGF 164) secreted by granulosa cells are involved in thecal angiogenesis during follicular development in the bovine ovary. The follicular fluid in the developing follicle includes a slight amount of the progesterone. However, the progesterone (P4) effects on VEGF120 and VEGF164 isoforms have not been well characterized in the bovine granulosa cells. We investigated the effects of progesterone on the gene expression of hypoxia-inducible factor 1alpha (HIF-1alpha, transcription factor), VEGF120, VEGF164 and Flk-1, its receptors, in cultured bovine granulosa cells. Messenger RNA expression for HIF-1alpha, VEGF120, VEGF164 and Flk-1 was quantified using real-time PCR methods. The levels of VEGF120, HIF-1alpha and Flk-1 mRNAs were increased significantly by P4 at a concentration of 10ng/ml. In contrast, the expression of VEGF 164 gene is inhibited by P4. The level of VEGF120 and Flk-1 mRNAs in the granulosa cells treated with 10ng/ml progesterone plus 1ng/ml estradiol significantly decreased compared with progesterone alone. In contrast, the addition of 1ng/ml estradiol to the culture medium increased the expression of VEGF164 gene. In conclusion, our data demonstrated that progesterone might stimulate the expression of the VEGF120 via HIF-1alpha, transcription factor, in bovine granulosa cells. These results suggest the hormone-dependent expression pattern of VEGF isoforms during follicular development. Thus, our study suggested the expression of VEGF isoforms in granulosa cells might be controlled by a different pathway during follicle development in cow.
Ovarian localization
Oocyte, Granulosa, Theca, Luteal cells, Small luteal cells, Large luteal cells
Comment
Role of Vascular Endothelial Growth Factor in Maintenance of Pregnancy in Mice. Wada Y et al. It is well known that withdrawal of progesterone from the maternal circulation is a critical stimulus to parturition in rodents, such as rats and mice. However, mechanisms that determine the timing of progesterone withdrawal are not completely understood. In the present study, we examined whether the vascular endothelial growth factor (VEGF) system in the corpus luteum (CL) contributes to the regulation of circulating progesterone levels and acts as a determinant of the timing of parturition in mice. We found that reduction in the expression levels of VEGF and VEGF receptor-2 in the CL precedes the impairment of luteal circulation and a series of events leading to parturition (i.e., reduction of plasma progesterone, enhancement of myometrium contractility, and onset of parturition). Blocking of VEGF signaling by using the inhibitor of VEGFR tyrosine kinase KRN633 at mid-pregnancy caused a similar sequence of events and induced preterm birth. These results suggest that the VEGF system in the CL plays a critical role in maintaining a high level of circulating progesterone, and determining the timing of parturition in mice.
Endo T, et al reported Cyclic changes in expression of mRNA of vascular endothelial
growth factor, its receptors Flt-1 and KDR/Flk-1, and Ets-1 in
human corpora lutea.
To evaluate the expression of mRNA of vascular endothelial growth
factor (VEGF), its receptors FIt-1 and KDR/Flk-1, and Ets-1 in human corpora
lutea,
Fifteen corpora lutea were obtained during hysterectomy (5 in
the early luteal phase, 5 in the mid-luteal phase, and 5 in the late luteal
phase).
Human corpora lutea in early luteal phase and mid-luteal phase had
high VEGF mRNA expression. Expression of VEGF mRNA was significantly reduced
in the late luteal phase. Immunohistochemistry showed that VEGF protein was
expressed mainly in granulosa lutein cells and faintly in thecal lutein cells.
Staining of VEGF protein was decreased in human corpora lutea in the late
luteal phase. Expression of Flt-1 and KDR/Flk-1 mRNA was increased in the
early luteal phase and mid-luteal phase and decreased in the late luteal
phase. Immunohistochemistry showed that Flt-1 and KDR/Flk-1 proteins were
expressed mainly in granulosa lutein cells and faintly in thecal lutein cells
and endothelial cells in the early luteal phase and mid-luteal phase; their
protein staining was reduced in the late luteal phase. Expression of Ets-1
mRNA changed similarly to VEGF and its receptor mRNA in human corpora lutea
during the luteal phase.
Expression of Vascular Endothelial Growth Factor Receptors in Bovine Cystic Follicles. Isobe N et al. Cystic follicles have excess fluid derived from blood flow in the theca interna of the follicle; therefore, the vasculature network is related to cystic follicle formation. Vascular endothelial growth factor (VEGF) is a potent stimulator of blood vessel permeability and angiogenesis. The aim of this study was to examine the expression of VEGF receptors proteins and mRNA in cystic follicles to elucidate the VEGF system in cystic follicles. The expression of protein for VEGF receptors; fms-like-tyrosine kinase-1 (Flt-1) and foetal liver kinase-1 (Flk-1) was detected by the immunohistochemical method. The mRNA expression of Flt-1 and Flk-1 in cystic follicles was determined by RT-PCR. Concentration of oestradiol-17beta and progesterone in the follicular fluid of cystic follicles was determined using ELISA. Flt-1- and Flk-1 proteins were localized in granulosa and theca interna cells and endothelial cells of theca layers. The intensity of Flt-1 and Flk-1 immunoreaction was similar among cystic follicles with various ratios of oestradiol-17beta/progesterone concentrations. The expression of Flt-1 and Flk-1 mRNA was similar, regardless of the ratio of oestradiol-17beta to progesterone in follicular fluid. These results demonstrate that cystic follicles have both VEGF receptors in the granulosa and theca interna layers, which may be responsible for the increased permeability of microvessels, causing the accumulation of follicular fluid in cystic follicles.
KDR-LacZ-expressing cells are involved in ovarian and testis-specific vascular development, suggesting a role for VEGFA in the regulation of this vasculature. Bott RC et al. Our objectives were to evaluate kinase insert domain protein receptor (KDR)-?galactosidase (LacZ) expression as a marker for vascular development during gonadal morphogenesis and to determine whether any novel non-angiogenic KDR-LacZ expression was present in mouse testes or ovaries. Gonads were collected from mice expressing LacZ driven by the Kdr promoter (KDR-LacZ) from embryonic day 11 (E11) through postnatal day 60 (P60). At E11.5, mesonephric cells expressing KDR-LacZ seemed to migrate into the developing testis and surrounded developing seminiferous cords. Cells expressing KDR-LacZ appeared in the ovary with no apparent migration from the adjacent mesonephros, suggesting a different origin of endothelial cells. Testis organ cultures from E11 mice were treated with 8??M VEGFR-TKI, a vascular endothelial growth factor?A signal transduction inhibitor; subsequently, the amount of KDR-LacZ staining was reduced by 66%-99% (P<0.002), and the ability of KDR-expressing cells to form a densely organized vascular network was inhibited. Novel non-angiogenic KDR-LacZ staining was detected in the testis on specific subsets of germ cells at E16, E17, P4, P20, P30, and P60. In ovaries, staining was present on oocytes within oocyte cysts at E17 and within late secondary follicles of postnatal mice. Thus, KDR is an excellent marker for analyzing vascular development in the gonads. Inhibition of VEGFA signal transduction prevents the development of testis-specific vasculature. Furthermore, non-vascular KDR-LacZ staining suggests that KDR directly affects both spermatogenesis and somatic-oocyte interactions during gametogenesis.
Follicle stages
Antral, Preovulatory, Corpus luteum
Comment
Vascular endothelial growth factor (VEGF) is a potent mitogen and cytoprotective factor for vascular endothelial cells. Although VEGF is ubiquitously expressed, its role in non-vascular tissues is poorly understood. VEGF interacts with various cell-surface receptors to mediate its cellular effects. It previously has been thought that the VEGF receptor Flk-1/KDR, its main signaling receptor, was expressed exclusively by endothelial cells. However, in the present study using bovine and rodent models, Greenaway et al demonstrate that VEGF and Flk-1/KDR are co-expressed in ovarian granulosa cells. VEGF and Flk-1/KDR mRNA and protein were both detectable in follicle tissue sections and in in vitro cultured granulosa cells. Expression of both ligand and receptor increased in healthy follicles throughout follicular development. VEGF treatment of serum-starved and cytokine-exposed granulosa cells resulted in enhanced survival and this cytoprotection was ameliorated when Flk-1/KDR signaling was inhibited. Reduced expression of Flk-1/KDR was also associated with the onset and progression of follicle atresia, suggesting involvement in follicular health in vivo. The results of this study demonstrate for the first time expression of Flk-1/KDR in ovarian granulosa cells and identify a novel extravascular role for VEGF and its receptor in ovarian function.
Phenotypes
Mutations
1 mutations
Species: None
Mutation name: None
type: None fertility: None Comment: Vascular endothelial growth factor receptor 2-mediated angiogenesis is essential for gonadotropin-dependent follicle development
Zimmermann RC, et al .
Gonadotropins induce ovarian follicle growth that is coincident with increased follicular vasculature, suggesting a role of angiogenesis in follicle development. Functional studies performed in nonhuman primates show that administration of substances that inactivate VEGF block the development and function of preovulatory follicles as demonstrated by histological analysis or hormone measurements. Blockage of function of VEGF receptor 2 (VEGFR-2) alters follicular hormone secretion, suggesting that the intraovarian effect of VEGF might be mediated by this receptor. The specific mechanism by which follicular development was blocked in these previous studies remains unclear, however. Here we characterize the intraovarian role of VEGFR-2 activity on follicular development by choosing a model in which active feedback is absent, the prepuberally hypophysectomized mouse. Hypophysectomy prevents advanced follicle growth and maturation; however, follicle development to the preovulatory stage can be stimulated by administration of gonadotropins. We report that exogenously administered gonadotropins are unable to drive follicle development to the preovulatory stage in the presence of antiangiogenic agent, VEGFR-2-neutralizing Ab's. This inhibition of follicular development is caused by arrests to both angiogenesis and antrum formation. We conclude that the intraovarian VEGF/VEGFR-2 pathway is critical for gonadotropin-dependent angiogenesis and follicular development.