1 Division of Reproductive Sciences, Oregon National Primate Research Center, Oregon Health & Science University, Beaverton, OR 97006-3448 and 2 Division of Reproductive Endocrinology & Infertility, Department of Obstetrics & Gynecology, Oregon Health & Science University, Portland, OR 97239-3011, USA
3 Current address: 505 N.W. 185th Avenue, Beaverton, OR 97006-3448, USA
4 To whom correspondence should be addressed at: University Fertility Consultants, 1750 S.W. Harbor Way, Suite 100, Portland, Oregon, USA, 97201-5133, USA. e-mail: pattonp{at}ohsu.edu
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Abstract |
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Key words: controlled ovarian stimulation/ovarian hyperstimulation syndrome/soluble VEGF receptors/vascular endothelial growth factor
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Introduction |
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Aberrant production of angiogenic factors is implicated in numerous pathological states including ovarian cancer and pre-eclampsia (Sharkey et al., 1996; Geva and Jaffe, 2000
). Although the precise mechanism is unknown, several reports suggest that VEGF may play an important, yet poorly defined, role in the development of ovarian hyperstimulation syndrome (OHSS) (Krasnow et al., 1996
; Abramov et al., 1997
; Lee et al., 1997b
; Pellicer et al., 1999
). In support of this concept are studies that indicate increased levels of VEGF in serum, follicular fluid and peritoneal fluid in women who develop OHSS (Krasnow et al., 1996
; Lee et al., 1997b
; Agrawal et al., 1999
; Attini et al., 2002
). Serum VEGF levels are higher in women at risk for OHSS, and correlate with clinical course of the syndrome (Abramov et al., 1997
). In addition, anti-VEGF antibodies neutralize the vascular permeability activity of follicular fluids, and ascitic fluid obtained in women with OHSS (McClure and Healy, 1994
; Levin et al., 1998
). Another vasoactive factor implicated in the pathogenesis of OHSS is angiogenin. Angiogenin is a polypeptide produced by a variety of cells and is reported to be elevated in serum and ascitic fluid in women with severe OHSS (Aboulghar et al., 1998
).
While the studies summarized above indicate a link between VEGF levels and the development of OHSS, others have not (Kobayashi et al., 1998; Chen et al., 2000
; Enskog et al., 2001
). The lack of longitudinal studies that examine VEGF and the influence of circulating binding proteins (e.g. sVEGFR) on the levels of available VEGF expression contribute to this controversy. Because conflicting data exist concerning the peripheral production and diagnostic relevance of circulating angiogenic substances, we investigated the secretion patterns of angiogenic factors (VEGF-A and angiogenin) and sVEGFR in women undergoing ovarian stimulation for IVF who were considered at high risk for the development of OHSS during the follicular and luteal phases of controlled ovarian stimulation (COS) cycles, and during early pregnancy. In a comparative analysis, we performed similar experiments in the non-human primates during spontaneous and stimulated cycles using exogenous gonadotrophins, as a prelude to future mechanistic studies.
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Materials and methods |
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Study 1. Analysis of angiogenic factors and their soluble receptors in women undergoing COS for IVF
In a prospective observational study, patients were recruited from a population of women undergoing IVF at the infertility clinic at the Oregon Health & Science University. The study and consent form were approved by the Institutional Review Board. The methods of ovarian stimulation, sperm processing, and techniques for fertilization and embryo culture were previously described (Patton et al., 1999). Briefly, the ovarian stimulation protocol included using a long-acting GnRH agonist (0.5 mg twice daily, Lupron; TAP Pharmaceuticals, Inc., USA) administered after
2 weeks of oral contraceptive treatment. After biochemical evidence of pituitary suppression (serum estradiol <40 pg/ml), FSH or FSH/hMG (Serono Inc., USA) was given twice daily (225450 IU per day). Follicular response was monitored with serial pelvic ultrasound examinations and serum estradiol measurements. When at least two follicles were >17 mm, 10,000 IU of hCG (Serono Inc.) was given i.m., and transvaginal ultrasound-directed oocyte retrieval was scheduled 36 h later. At 1518 h post-insemination, oocytes were assessed for fertilization (the presence of two pronuclei). On the morning of day 3 post-insemination, embryos were assessed for cell number and degree of fragmentation. Embryo transfers occurred on day 3 or day 56. Day 3 embryo transfer was offered to women with <4 cleaving embryos on day 3 of culture and in women aged >36 years of age. Otherwise, embryos were held in extended culture and transferred at the blastocyst stage (day 56).
Women thought to be at high risk for OHSS were recruited for enrollment into the study based on the demonstration of any of the following criteria (Artini, 1998): (i) exaggerated response to gonadotrophins with a projected peak estradiol level of >2000 pg/ml; (ii) an anticipated high number of pre-ovulatory follicles (>20) on the day of hCG administration; (iii) history of polycystic ovary syndrome with ultrasonographic evidence of polycystic ovaries. The diagnosis of OHSS was made using criteria of Golan et al. (1989
).
During the IVF cycle, pelvic ultrasonography and blood collection were performed at each clinic visit. Serum samples were collected following 35 days of gonadotrophin therapy, and then every 13 days up to the day of hCG administration. An additional blood sample (for haematocrit analysis) was drawn during the period of gonadotrophin stimulation. Additional serum and blood samples were also obtained on the day of hCG administration (day 0), day of oocyte retrieval (day 2), embryo transfer (day 3 or day 56), and on the day of the first pregnancy test (day 1921). In women who became pregnant, serum samples were collected weekly for an additional 4 weeks.
Study 2. Analysis of VEGF levels in monkeys during natural and COS cycles and in simulated early pregnancy
The protocol for animal studies was approved by the ONPRC IACUC committee.
Natural cycles
Beginning with menses, daily serum samples were obtained from female rhesus monkeys exhibiting regular cycles (n = 8) and were continued until the next menstrual period.
COS with simulated early pregnancy
Female rhesus monkeys exhibiting regular menstrual cycles (n = 5) received recombinant (r) human gonadotrophins (Serono, Inc.) following a modified COS protocol (VandeVoort et al., 1988; Chaffin et al., 1999
). Specifically, to maximize multiple pre-ovulatory follicle development, the daily dose for gonadotrophin treatment was increased by 50%. Briefly, beginning at menses, monkeys received rhFSH (30 IU, three times daily, 6 days) followed by rhFSH/rhLH (30 IU/30 IU, three times daily, for 23 days). A GnRH antagonist (Antide; Serono, Inc.) was concomitantly administered to prevent an endogenous LH surge. Based on ultrasound evaluation, an ovulatory dose of rhCG (1000 IU) was administered and follicle aspiration performed 27 h later and oocytes were collected. Beginning on day 9 of the luteal phase, the same animals received increasing doses of rhCG (15360 IU, twice daily), for 6 days to simulate early pregnancy (Duffy and Stouffer, 1997
). Serum samples were obtained beginning on the day of FSH treatment and were continued daily until menses.
Analysis of serum samples from women and monkeys
Blood samples were allowed to clot and the supernatant was separated and stored at 20°C until assay. Serum samples were analysed for estradiol (E2; Elecsys 2010), progesterone (Elecsys 2010), and free VEGF, sVEGF-R1 and -R2, and angiogenin (R&D Systems, USA), and free plus bound (total) VEGF (Cytimmune Sciences, USA). Pooled samples were included in all assays to confirm accuracy. Inter-assay variations for progesterone and E2 were 6.0 and 4.9% respectively. Inter- and intra-assay variations for free VEGF were 8.3 and 12.1%; total VEGF, 9.1 and 13.3%; sVEGF-R1, 7.1 and 10.2%; sVEGF-R2, 8.9 and 12.9%; and angiogenin, 6.6 and 9.1% respectively. VEGF assays of monkey samples were previously validated against human VEGF (Christenson and Stouffer, 1997). Blood samples for haematocrit analysis were performed using an independent laboratory (Quest Diagnostics, USA).
Results were analysed via analysis of variance followed by StudentNeumanKuels tests (within the group of pregnant and non-pregnant women) or t-tests (between pregnant and non-pregnant women) (NWA Statpac, USA). Data are expressed as mean ± SEM. A significant difference was defined as P < 0.05.
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Results |
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Ovarian steroid production
The patterns of serum estradiol and progesterone for the pregnant and non-pregnant groups are presented in Figures 1A and B respectively. The results display the expected rise in estradiol concentration which peaks on the day of hCG injection, followed by the decline in serum estradiol and rise in serum progesterone in the luteal phase (day 39 post hCG injection). During the process of ovarian stimulation, there were no significant differences in the pattern of serum estradiol secretion between the two groups. As expected, estradiol and progesterone levels in the pregnant group were higher by day 20, compared to the non-pregnant group, reflecting the continued luteal function until replaced by placental steroidogenesis.
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Soluble VEGF receptors
The serum levels of sVEGF-R1 and -R2 are presented in Figure 3A and B respectively. Higher levels of sVEGF-R1 were observed in the non-pregnant group during the time-points associated with gonadotrophin stimulation (day 10, 50.2 ± 16 versus 18.7 ± 7.5; day 0, 48 ± 15.8 versus 17.5 ± 6.7 pg/ml; non-pregnant versus pregnant, P < 0.05). There were no appreciable changes in sVEGF-R1 levels during follicular stimulation, or in the subsequent early luteal phase. However, between days 30 and 40 following hCG administration, an abrupt rise (P < 0.05) in serum levels of sVEGF-R1 was noted in pregnant women. Thereafter, sVEGF-R1 levels continued to rise with peak levels (800 pg/ml) occurring at the end of the sampling interval. In contrast, sVEGF-R2 levels declined slightly during the interval of ovarian stimulation in pregnant women. There was a significant but minimal decline in sVEGF-R2 levels after pregnancy initiation compared to follicular phase levels (day 10 versus day 40 or day 50, P < 0.05). Levels of sVEGF-R2 were higher than sVEGF-R1 and ranged between 9 and 13 ng/ml.
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Table II summarizes the data from two women where an embryo transfer was postponed due to OHSS concerns (cases 1 and 2), and another woman who developed OHSS after embryo transfer (case 3). In all three cases, peak estradiol levels (range, 31004100 pg/ml) were similar to those of the study population. However, in cases 2 and 3, higher progesterone values in the luteal phase and early pregnancy, and higher levels of free VEGF (>400 pg/ml) plus lower levels of total VEGF and sVEGF-R2 were observed during early pregnancy compared to controls. In contrast, case 1 exhibited a very different pattern with low-to-normal free VEGF, and elevated total VEGF and sVEGF-R2 levels. Thus, cases 2 and 3 displayed greater free:total VEGF ratios, whereas case 1 had a lower free:total VEGF ratio compared to time-matched controls. Serum angiogenin levels displayed a quite different pattern. In severe OHSS, angiogenin levels were lower on day 0, day 21 and day 30 (case 3), whereas angiogenin levels were higher on day 0 (cases 1 and 2) and day 2 (case 1) compared to pregnant controls.
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Discussion |
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Angiogenin is glycopeptide made by a variety of tissues and is an important mediator of neovascularization (Shestenko et al., 2001). Angiogenin levels tended to decrease during gonadotropin stimulation and rose during the luteal phase, particularly in non-pregnant women. Interestingly, angiogenin values were higher in pregnant women during gonadotropin treatment compared to non-pregnant women. In a previous case report, increased angiogenin levels were detected in serum and ascitic fluid in a woman who developed OHSS (Aboulghar et al., 1998
). However, we observed no significant change in angiogenin levels with rising hCG levels consistent with previous studies (Hayashi et al., 2000
). Furthermore, because circulating angiogenin levels were lower in the single patient who developed severe OHSS, but were higher in two women where embryo transfer was postponed secondary to concerns over OHSS (Table II), the role of circulating angiogenin as an endocrine agent in the pathogenesis of OHSS is unclear. However, the possibility exists that angiogenin in combination with other vasoactive factors may contribute to the development of OHSS.
Only limited longitudinal data exist concerning the expression of VEGF and soluble VEGF receptor proteins in women undergoing COS. Previous analyses generally focused on only a few of the time points between gonadotrophin treatment and embryo transfer, or on data from women who developed overt OHSS at a time point remote from hCG. Furthermore, the effects of pregnancy on circulating VEGF and soluble receptor levels in women at risk for OHSS has not been assessed. Therefore, we performed a prospective study that examined the circulating levels of these factors during follicular stimulation, the luteal phase and for the first time examined the dynamics of VEGF and soluble receptor proteins during early pregnancy. Our results indicate that the levels of VEGF and soluble receptor proteins exhibit dynamic changes during COS cycles and early pregnancy. In addition, subtle differences may exist in the patterns of secretion of angiogenic factors between women who ultimately conceive (pregnant group) and women who do not (non-pregnant group).
Changes in circulating VEGF or soluble receptor levels did not occur during the interval between hCG administration and oocyte retrieval. These findings are consistent with some (Ludwig et al., 1999; Chen et al., 2000
), but not all (Artini et al., 1998
, 2002; Agrawal et al., 1999
; Pellicer et al., 1999
) studies. One drawback of this study is that VEGF was measured in serum. Serum concentrations of VEGF can be 810-fold higher than plasma levels secondary to the release of VEGF from activated platelets and other cellular components found in blood (Verheul et al., 1997
; Maloney et al., 1998
), and differences in the assessment of VEGF circulating patterns among published studies are attributed, in part, to the use of serum to measure VEGF rather that plasma (Ludwig et al., 1999
). We recognize that measures of VEGF using serum samples could reflect both ovarian and nonovarian sources of VEGF. However, our results are consistent with previous studies using either serum (Chen et al., 2000
) or plasma (Ludwig et al., 1999
). More importantly, our unique observation that VEGF levels decrease following implantation and fall to virtually non-detectable levels with pregnancy cannot be readily attributed to the use of serum samples. Conceivably, VEGF release from both reproductive tissues (e.g. ovary, placenta) and non-reproductive tissues (e.g. platelets, granulocytes) could contribute to pathologic conditions associated with excessive VEGF production. We strongly recommend that future studies should concentrate on the measurement of plasma VEGF to address these important considerations.
We did observe a significant increase in both free and total VEGF during the early luteal phase in women who conceived. In the non-pregnant group, there were no significant changes in either free or total VEGF levels during the luteal phase, but the patterns in circulatory levels were similar to the pregnant group. The difference between pregnant and non-pregnant women is not likely related to steroidogenic function or response to gonadotropin, since peak estradiol and progesterone levels (in the follicular and luteal phase, respectively), dose of gonadotrophin and numbers of oocytes collected or embryos transferred were similar. Increased circulating luteal phase VEGF levels in pregnant women could indicate subtle differences in the response or quality of luteal VEGF producing components, particularly in younger women. Alternatively, given the limited number of subjects at risk for OHSS recruited in this study, larger studies are necessary to confirm that patterns of VEGF secretion during the luteal phase for pregnant and non-pregnant women are different.
Free VEGF levels initially rose in pregnant women during the luteal phase in COS cycles, but progressively fell reaching undetectable levels by day 40. By day 30 the decline in circulating free VEGF was associated with a corresponding rise in sVEGF-R1. These contrasting changes in circulating VEGF and soluble receptors levels may provide important insights concerning the regulation of circulating free VEGF during natural and COS cycles, early pregnancy, and the potential mechanisms involved in the pathogenesis of OHSS. During the natural cycle, VEGF is detectable in follicular fluid following an ovulatory bolus of gonadotropin (Yan et al., 1993; Neulen et al., 1995
) and secreted by luteinizing granulosa cells (Lee et al., 1997a
; Hazzard et al., 2000
; Molskness and Stouffer, 2002
; Martinez-Chequer et al., 2003
), but circulating levels of free VEGF are low (Unkila-Kallio et al., 2000
; Licht et al., 2001
) secondary to the presence of soluble VEGF receptors and other binding proteins (
2 macroglobulin, albumin) (Aboulghar et al., 1998
, 2002; McElhinney et al., 2002
). As a result, free VEGF is tightly controlled, and OHSS rarely occurs during the natural cycle.
In contrast to the natural cycle, COS cycles are associated with exaggerated ovarian production of VEGF that results in an increase in circulating levels of free VEGF during the early luteal phase in women at risk for OHSS. Why some women develop OHSS during COS cycles and others do not is incompletely understood. It is interesting to speculate that early onset OHSS (Mathur et al., 2000) occurs when exaggerated ovarian VEGF production during the early luteal phase greatly exceeds the capacity of neutralizing VEGF binding proteins and/or soluble receptors. In support of this idea are studies that demonstrate higher VEGF levels at the time of embryo transfer in women who develop OHSS (Ludwig et al., 1999
), and that VEGF levels continue to rise during the luteal phase in women who develop severe OHSS, but not in women without OHSS (Agrawal et al., 1999
). These data suggest that in most COS cycles physiological concentrations of binding proteins and soluble receptors can accommodate rising levels of ovarian-derived VEGF during the luteal phase, but that OHSS may occur when fVEGF/tVEGF ratios are dramatically altered. Whether other angiogenic factors contribute or modify VEGF actions in the pathogenesis of OHSS is currently unknown, but represents an important area of future investigation.
The production of placental sVEGF-R1 may represent an additional physiologic mechanism that regulates the potential adverse effects of rising levels of free VEGF, particularly in the development of delayed onset OHSS. Alternate splicing of pre-mRNA for VEGF-R1 results in a full-length membrane bound receptor (VEGF-R1) and truncated soluble receptor (sVEGF-R1). Free VEGF is inactivated after binding to sVEGF-R1, or dimerization of sVEGF-R1 with VEGF-R2 (Kendall and Thomas, 1993; Kendall et al., 1996
). During early pregnancy, sVEGF-R1 can be detected in the peripheral circulation (Banks et al., 1998
; Clark et al., 1998
), and has a 10-fold higher affinity for VEGF compared to VEGF-R2. Rising serum sVEGF-R1 levels after implantation would result in decreased levels of bioavailable VEGF and/or decreased activity of free VEGF, providing protection during spontaneous conceptions and possibly in women during COSembryo transfer cycles displaying rising levels of VEGF during the luteal phase. In the single patient of our study who developed severe OHSS, free VEGF levels were higher and sVEGF-R1 levels were significantly lower than women who did not develop severe OHSS. It is interesting to speculate that a delayed, altered, or insufficient production of sVEGF-R1, an excessive production of free VEGF or a combination of both may be critical events in the development of OHSS. Whether the concentration or patterns of expression of free VEGF, sVEGF-R1, or other binding proteins correlates with the development of OHSS warrants further investigation.
Using a protocol of COS similar to that used in humans, with repeated hCG injections during the luteal phase to mimic early pregnancy, we attempted to create a nonhuman primate model for OHSS. Although none of the animals developed any degree of OHSS, we observed supraphysiologic endocrine profiles similar to those in humans (Figure 4). Furthermore, despite the fact that free VEGF was undetectable in the peripheral circulation during ovarian stimulation, the luteal phase, or following the pseudo-pregnancy hCG regimen, total VEGF levels were similar to those seen in human studies. In the non-human primate, mRNA transcripts for VEGF can be detected in granulosa cells (Hazzard et al., 1999) and VEGF is secreted by luteinized granulosa cells (Christenson and Stouffer, 1997
; Martinez-Chequer et al., 2003
), and luteal cells (Molskness and Stouffer, 2002
). In addition, VEGF protein can be identified in follicular fluid extracts from animals at the time of oocyte recovery (Hazzard et al., 1999
). Therefore, the failure to identify free VEGF in the systemic circulation was a surprising finding. The comparison of VEGF binding proteins in the nonhuman primate to those in women could provide important insights on the pathogenesis of OHSS. Alternatively, the current results are also consistent with a hypothesis that, like circulating progesterone levels, VEGF levels and possibly luteal secretion of VEGF during gonadotropin stimulation cycles in rhesus macaques are lower when compared to those in women. The low level of free VEGF, combined with the lack of OHSS symptoms, suggest that this macaque could serve as a model for examining the ability of administered VEGF to cause OHSS in natural and COS cycles.
In summary, this study demonstrated the dynamic pattern of free and total VEGF-A, plus its soluble VEGF receptors (-R1 and -R2), during COS cycles in women, especially following the ovulatory hCG bolus and pregnancy initiation. While attention to date has focused on VEGF production, it is apparent that further consideration of the role of VEGF-A in ovarian function and dysfunction should consider the expression and actions of all components of the VEGF-A receptor binding protein system. Alterations in free: bound VEGF-A, as influenced by VEGF synthesis but also the production and systemic or local levels of binding proteins, could lead to ovarian dysfunction. Excess (elevated free:total) and deficient (reduced free:total) VEGF could result in an imbalance with other angiogenic factors (e.g. angiogenin) resulting in local or systemic vascular dysfunction.
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Acknowlegements |
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References |
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---|
Aboulghar MA, Mansour RT, Serour GI, Elhelw BA and Shaarawy M (1998) Elevated concentrations of angiogenin in serum and ascitic fluid from patients with severe ovarian hyperstimulation syndrome. Hum Reprod 13,20682071.[Abstract]
Aboulghar M, Evers JH and Al-Inany H (2002) Intra-venous albumin for preventing severe ovarian hyperstimulation syndrome (Cochrane Review). Cochrane Database Syst Rev 4,CD001302.
Abramov Y, Barak V, Nisman B and Schenker JG (1997) Vascular endothelial growth factor plasma concentrations correlate to the clinical picture in severe ovarian hyperstimulation syndrome. Fertil Steril 67,261265.[CrossRef][ISI][Medline]
Agrawal R, Tan SL Wild, S, Sladkevicius P, Engmann L, Payne N, Bekir J, Campbell S, Conway G and Jacobs H (1999) Serum vascular endothelial growth factor concentrations in in vitro fertilization cycles predict the risk of ovarian hyperstimulation syndrome. Fertil Steril 71,287293.[CrossRef][ISI][Medline]
Artini PG, Fasciani A, Monti M, Luisi S, DAmbrogio G and Genazzani AR (1998) Changes in vascular endothelial growth factor levels and the risk of ovarian hyperstimulation syndrome in women enrolled in an in vitro fertilization program. Fertil Steril 70,560564.[CrossRef][ISI][Medline]
Artini PG, Monti M, Fasciani A, Battaglia C, Ambrogio GD and Genazzani AR (2002) Vascular endothelial growth factor, interleukin-6 and interleukin-2 in serum and follicular fluid of patients with ovarian hyperstimulation syndrome. Eur J Obstet Gynecol Reprod Biol 101,169174.[CrossRef][ISI][Medline]
Banks RE, Forbes MA, Searles J, Pappin D, Canas B, Rahman D, Kaufmann S, Walters CE, Jackson A, Eves P et al (1998) Evidence for the existence of a novel pregnancy-associated soluble variant of the vascular endothelial growth factor receptor, Flt-1. Mol Hum Reprod, 4, 377386.[Abstract]
Chaffin CL, Hess DL and Stouffer RL (1999) Dynamics of periovulatory steroidogenesis in the rhesus monkey follicle after ovarian stimulation. Hum Reprod 14,642649.
Chen C-D, Chen H-F, Lu H-F, Chen S-U, Ho H-N and Yang Y-S (2000) Value of serum and follicular fluid cytokine profile in the prediction of moderate to severe ovarian hyperstimulation syndrome. Hum Reprod 15,10371042.
Christenson LK and Stouffer RL (1997) Follicle-stimulating hormone and luteinizing hormone/chorionic gonadotropin stimulation of vascular endothelial growth factor production by macaque granulosa cells from pre- and periovulatory follicles. J Clin Endocrinol Metab 82,21352142.
Clark DE, Smith SK, He Y, Day KA, Licence DR, Corps AN, Lammoglia R and Charnock-Jones DS (1998) A vascular endothelial growth factor antagonist is produced by the human placenta and released into the maternal circulation. Biol Reprod 59,15401548.
deVries C, Escobedo JA, Ueno H, Houck K, Ferrarra N and Williams LT (1992) The fms-like tyrosine kinase, a receptor for vascular endothelial cell growth factor. Science 255,989991.[ISI][Medline]
Dickson SE, Bicknell R and Fraser HM (2001) Mid-luteal angiogenesis and function in the primate is dependent on vascular endothelial growth factor. J Endocrinol 168,409416.
Duffy DM and Stouffer RL (1997) Gonadotropin versus steroid regulation of the corpus luteum of the rhesus monkey during simulated early pregnancy. Biol Reprod 57,14511460.[Abstract]
Enskog A, Nilsson L and Brannstrom M (2001) Plasma levels of free vascular endothelial growth factor165 (VEGF165) are not elevated during gonadotrophin stimulation in in vitro fertilization (IVF) patients developing ovarian hyperstimulation syndrome (OHSS): results of a prospective cohort study with matched controls. Eur J Obstet Gynecol Reprod Biol 96,196201.[CrossRef][ISI][Medline]
Ferrara N and Davis-Smyth T (1997) The biology of vascular endothelial growth factor. Endocr Rev 18,425.
Geva E and Jaffe RB (2000) Role of vascular endothelial growth factor in ovarian physiology and pathology. Fertil Steril 74,429438.[CrossRef][ISI][Medline]
Golan A, Ron-El R, Herman A, Soffer Y, Weinraub Z and Caspi E (1989) Ovarian hyperstimulation syndrome: an update review. Obstet Gynecol Surv 44,430440.[Medline]
Hayashi K, Yanagihara T and Hata T (2000) Serum angiogenin levels during menstrual cycle and pregnancy. Gynecol Obstet Invest 50,712.[CrossRef][Medline]
Hazzard TM and Stouffer RL (2000) Angiogenesis in ovarian follicular and luteal development. In Arulkumaran S (ed) Clinical Obstetrics & Gynaecology. Angiogenesis in the female reproductive tract. Baillière Tindall, London, UK, pp 883900.
Hazzard TM, Molskness TA, Chaffin CL and Stouffer RL (1999) Vascular endothelial growth factor (VEGF) and angiopoietin regulation by gonadotrophin and steroids in macaque granulosa cells during the peri-ovulatory interval. Mol Hum Reprod 5,11151121.
Hazzard TM, Christenson LK and Stouffer RL (2000) Changes in expression of vascular endothelial growth factor (VEGF), angiopoietin (Ang)-1 and Ang-2 in the macaque corpus luteum during the menstrual cycle. Mol Hum Reprod 6,993998.
Hazzard TM, Xu F and Stouffer RL (2002) Injection of soluble vascular endothelial growth factor receptor 1 into the preovulatory follicle disrupts ovulation and subsequent luteal function in rhesus monkeys. Biol Reprod 67,13051312.
Kendall RL, Wang G and Thomas KA (1996) Identification of a natural soluble form of the vascular endothelial growth factor receptor, Flt-1, and its heterodimerization with KDR. Biochem Biophys Res Commun 226,324328.[CrossRef][ISI][Medline]
Kendall RL and Thomas KA (1993) Inhibition of vascular endothelial cell growth factor activity by an endogenously encoded soluble receptor. Proc Natl Acad Sci USA 90,1070510709.[Abstract]
Kobayashi H, Okada Y, Asahina T, Gotoh J and Terao T (1998) The kallikrein-kinin system, but not vascular endothelial growth factor, plays a role in the increased vascular permeability associated with ovarian hyperstimulation syndrome. J Mol Endocrinol 20,363374.
Krasnow JS, Berga SL, Guzick DS, Zeleznik AJ and Yeo K-T (1996) Vascular permeability factor and vascular endothelial growth factor in ovarian hyperstimulation syndrome: a preliminary report. Fertil Steril 65,552555.[ISI][Medline]
Lee A, Christenson LK, Patton PE and Stouffer RL (1997a) Vascular endothelial growth factor production by human luteinized granulosa cells in vitro. Hum Reprod 12,27562761.[Abstract]
Lee A, Christenson LK, Stouffer RL, Burry KA and Patton PE (1997b) Vascular endothelial growth factor levels in serum and follicular fluid of patients undergoing in vitro fertilization. Fertil Steril 68,305311.
Levin ER, Rosen GF, Cassidenti DL, Yee B, Meldrum D, Wisot A and Pedram A (1998) Role of vascular endothelial cell growth factor in ovarian hyperstimulation syndrome. J Clin Invest 102,19781985.
Licht P, Neuwinger J, Fischer O, Siebzehnrubl E and Wildt L (2001) Peripheral levels of vascular endothelial growth factor (VEGF) are higher in gonadotropin stimulated as compared to natural ovarian cycles. Exp Clin Endocrinol Diabetes 109,345349.[CrossRef][ISI][Medline]
Ludwig M, Jelkmann W, Bauer O and Diedrich K (1999) Prediction of severe ovarian hyperstimulation syndrome by free serum vascular endothelial growth factor concentration on the day of human chorionic gonadotropin administration. Hum Reprod 14,24372441.
Maloney JP, Silliman CC, Ambruso DR, Wang J, Tuder RM and Voelkel NF (1998) In vitro release of vascular endothelial growth factor during platelet aggregation. Am J Physiol 275 (Heart Circ Physiol 44),H1054H1061.
Martinez-Chequer JC, Stouffer RL, Hazzard TM, Patton PE and Molskness TA (2003) Insulin-like growth factors-1 and -2, but not hypoxia, synergize with gonadotropin hormone to promote vascular endothelial growth factor-A secretion by monkey granulosa cells from preovulatory follicles. Biol Reprod 68,11121118.
Mathur RS, Akande AV, Keay SD, Hunt LP and Jenkins JM (2000) Distinction between early and late ovarian hyperstimulation syndrome. Fertil Steril 73,901907.[CrossRef][ISI][Medline]
McClure N and Healy DL (1994) Vascular endothelial growth factor as a capillary permeability agent in ovarian hyperstimulation syndrome. Lancet 344,235236.[ISI][Medline]
McElhinney B, Ardill J, Caldwell C, Lloyd F and McClure N (2002) Ovarian hyperstimulation syndrome and assisted reproductive technologies: why some and not others? Hum Reprod 17,15481553.
Molskness TA and Stouffer RL (2002) Hypoxia, but not gonadotropin, stimulates vascular endothelial growth factor production by primate luteal cells in vitro. Biol Reprod 66(Suppl 1)283284 (abstract 457).
Neulen J, Yan Z, Raczek S, Weindel K, Keck C, Welch HA, Marme D and Breckwoldt M (1995) Human chorionic gonadotropin-dependent expression of vascular endothelial growth factor/VP factor in human granulosa cells: importance in ovarian hyperstimulation syndrome. J Clin Endocrinol Metab 80,19671971.[Abstract]
Patton PE, Sadler-Fredd K, Burry KA, Gorrill MJ, Johnson A and Larson JM (1999) Development and integration of an extended embryo culture program. Fertil Steril 72,418422.[CrossRef][ISI][Medline]
Pellicer A, Albert C, Mercader A, Bonilla-Musoles F, Remohi J and Simon C (1999) The pathogenesis of ovarian hyperstimulation syndrome: in vivo studies investigating the role of interleukin-1, interleukin-6, and vascular endothelial growth factor. Fertil Steril 71,482489.[CrossRef][ISI][Medline]
Rowe AJ, Morris KD, Bicknell R and Fraser HM (2002) Angiogenesis in the corpus luteum of early pregnancy in the marmoset and the effects of vascular endothelial growth factor immunoneutralization on establishment of pregnancy. Biol Reprod 67,11801188.
Sharkey AM, Cooper JC, Balmforth JR, McLaren J, Clark DE, Charnock-Jones DS, Morris NH and Smith SK (1996) Maternal plasma levels of vascular endothelial growth factor in normotensive pregnancies and in pregnancies complicated by pre-eclampsia. Eur J Clin Invest 26,11821185.[ISI][Medline]
Shestenko O, Nikonov S and Mertvetsov N (2001) Angiogenin and its function in angiogenesis. Mol Biol 35,294314.[CrossRef][ISI]
Terman B, Dougher-Vermazen M, Carrion ME, Dimitrov D, Armellino DC, Gospodarowicz D and Böhlen P (1992) Identification of the KDR tyrosine kinase as a receptor for vascular endothelial cell growth factor. Biochem Biophys Res Commun 187,15791586.[ISI][Medline]
Unkila-Kallio L, Vuorela-Vepsalainen P, Tiitinen A, Halmesmaki E and Ylikorkala O (2000) No cyclicity in serum vascular endothelial growth factor during normal menstrual cycle but significant luteal phase elevation during an in vitro fertilization program. Am J Reprod Immunol 43,2530.[CrossRef][ISI][Medline]
VandeVoort CA, Stouffer RL, Molskness TA and Ottobre JS (1988) Chronic exposure of the developing corpus luteum in monkeys to chorionic gonadotropin: persistent progesterone production despite desensitization of adenylate cyclase. Endocrinology 122,18761882.[Abstract]
Verheul HM, Hockman K, Luykx-de Bakker S, Eckman CA, Folman CC, Broxterman, HJ and Pinedo, HM (1997) Transporter of vascular endothelial growth factor. Clin Cancer Res 3,21872190.[Abstract]
Yan Z, Welch HA, Bernart W, Breckwoldt M and Neulen J (1993) Vascular endothelial growth factor (VEGF) messenger ribonucleic acid (mRNA) expression in luteinized human granulosa cells in vitro. J Clin Endocrinol Metab 77,17231725.[Abstract]
Zimmerman RC, Xiao E, Bohlen P and Ferin M (2002) Administration of antivascular endothelial growth factor receptor 2 antibody in the early follicular phase delays follicular selection and development in the rhesus monkey. Endocrinology 143,24962502.
Submitted on June 25, 2003; resubmitted on November 21, 2003; accepted on November 25, 2003.