Protective actions of microalgae against endogenous and exogenous advanced glycation endproducts (AGEs) in human retinal pigment epithelial cells

The formation and accumulation of advanced glycation endproducts (AGEs) is a key pathophysiological process involved in various diabetic complications such as diabetic retinopathy. In the present study, for the first time, protective effects of three microalgal strains, including their extracts and active compounds, against both endogenous and exogenous AGEs in cell-based models were investigated. Results showed that in cultured human-derived retinal pigment epithelial ARPE-19 cells, the extract of Chlorella zofingiensis and its nutritional ingredient astaxanthin exhibited significant inhibitory effects on the formation of endogenous N(ε)-carboxymethyllysine (CML), a key AGE representative, through the suppression of intracellular oxidative stress. On the other hand, extracts of Chlorella zofingiensis, Chlorella protothecoides and Nitzschia laevis as well as their nutritional ingredients, namely astaxanthin, lutein and eicosapentaenoic acid (EPA), attenuated the deleterious effects induced by exogenous AGEs, such as cell proliferation and mRNA upregulation of vascular endothelial growth factor (VEGF) and matrix metalloproteinases (MMP)-2, which are critical steps involved in the pathogenesis of diabetic retinopathy. These results suggested the positive roles of astaxanthin, lutein and EPA in controlling the development of diabetes. These microalgae, therefore, might be regarded as beneficial foods and preventive agent choices for patients with diabetic retinopathy.     

黄酮类化合物干预糖尿病视网膜病变的研究进展

糖尿病视网膜病变是糖尿病患者中最常见的微血管并发症,也是全世界造成失明的主要原因之一。人体内活性氧过量产生导致的氧化损伤是糖尿病视网膜病变的主要发病机制。黄酮类化合物普遍存在于植物膳食中,具有抗氧化、抗炎、降血糖、清除自由基等多种生理活性。近年来,越来越多的研究表明,黄酮类化合物对糖尿病视网膜病变有显著的干预效果。本文综述了近年来国内外对黄酮类化合物抗糖尿病视网膜病变的研究进展,以期为黄酮类化合物的进一步开发和应用提供理论参考和研究思路。     

The role of progesterone in endometrial angiogenesis in pregnant and ovariectomised mice

The role of progesterone (and oestrogen) in endometrial angiogenesis remains controversial. The aims of this study were to quantify endometrial angiogenesis in pregnant mice and to investigate the role of progesterone in promoting endothelial cell proliferation in ovariectomized mice. Uteri were collected on days 1 to 4 of pregnancy when circulating progesterone concentrations were increasing, prior to implantation. Before dissection, mice were injected with bromodeoxyuridine (BrdU) enabling proliferating endothelial cells to be quantified with CD31/BrdU double-immunohistochemistry. There was a significant increase in proliferating endothelial cells on day 3 of pregnancy when plasma progesterone also increased. To determine if this endothelial cell proliferation was due to progesterone, an experiment was performed on ovariectomised mice. One group was treated with a single oestradiol injection on day 8 after ovariectomy, followed by a no-treatment day and three consecutive daily injections of progesterone. Other groups were treated with either the vehicle, oestradiol or progesterone injections only; all were dissected on day 13 following ovariectomy. Unexpectedly, mice treated with progesterone-only had the highest amount of endothelial cell proliferation and oestrogen priming was found to significantly reduce this progesterone-induced endothelial cell proliferation. To determine if this proliferation is mediated by vascular endothelial growth factor (VEGF), a further experiment in which VEGF anti-serum was administered concurrently with the progesterone injections was performed. Endothelial cell proliferation was reduced but not abolished suggesting progesterone-induced endometrial angiogenesis is only partly mediated by VEGF. Results indicate that oestrogen priming is not required for progesterone to stimulate endometrial endothelial cell proliferation and that oestrogen inhibits progesterone-induced angiogenesis in ovariectomised mice.     

Mast cell degranulation in rat uterine cervix during pregnancy correlates with expression of vascular endothelial growth factor mRNA and angiogenesis

Vascular growth of the uterine cervix during pregnancy is associated with mast cell (MC) degranulation. To better understand the mechanism underlying this process, uterine cervices of intact pregnant rats were dissected and endothelial cell proliferation was measured by a bromodeoxyuridine incorporation technique. Total vascular endothelial growth factor (VEGF) mRNA expression and the relative abundance of VEGF splice variants (120, 164, and 188) were determined by RT-PCR. VEGF protein expression was evaluated by immunohistochemistry. To investigate the role of MCs on cervical angiogenesis, a second set of pregnant animals were treated with an MC stabilizer (disodium cromoglycate) to inhibit MC degranulation. Furthermore, 17beta-estradiol (E(2)) serum levels were established by RIA. In intact pregnant rats, VEGF mRNA expression was positively correlated with endothelial cell proliferation and circulating E(2) levels. All selected splice variants of VEGF gene were detected and their relative abundance did not show any change throughout pregnancy. Animals treated with disodium cromoglycate showed a decrease in endothelial cell proliferation and in VEGF mRNA expression compared with controls. Relative abundance of VEGF mRNA splice variants and E(2) serum levels showed no differences between these experimental groups. These results show a time-dependent correlation between VEGF mRNA expression and E(2) serum levels in the uterine cervix of intact pregnant rats, while MC stabilizer-treated animals reduced the VEGF expression without modifying E(2) serum levels. We suggest that cervical angiogenesis during pregnancy could be regulated by a mechanism which involves endogenous E(2) and chemical mediators stored in MC granules via a VEGF-dependent pathway.     

Human endometrial angiogenesis

Angiogenesis is the development of new microvessels from existing vessels, a process that involves microvascular endothelial cells. Physiological angiogenesis rarely occurs in adults except in the ovary and endometrium during the reproductive life of females. Angiogenesis occurs by sprouting and non-sprouting mechanisms. Since endothelial sprouts are not observed in human endometrium, we hypothesized that non-sprouting mechanisms such as intussusception and elongation are involved in endometrial angiogenesis. The demand for angiogenesis differs spatially and temporally in the endometrium: angiogenesis occurs in the basalis layer during menstruation and in the functionalis and subepithelial capillary plexus during the proliferative and early secretory stages. Most studies have failed to demonstrate a link between expression of endometrial angiogenic factors and new vessel growth. However, we demonstrated recently a strong relationship between vascular endothelial growth factor (VEGF) immunolocalized in in-travascular neutrophils and endothelial cell proliferation in each of the subepithelial capillary plexus, functionalis and basalis regions of the human endometrium. Our data also indicate that focal neutrophil VEGF has a role in the development of the subepithelial capillary plexus and functionalis microvessels during the proliferative phase of the menstrual cycle. We propose that neutrophils are an intravascular source of VEGF for vessels that undergo angiogenesis by intussusception and elongation.     

Administration of vascular endothelial growth factor Trap during the 'post-angiogenic' period of the luteal phase causes rapid functional luteolysis and selective endothelial cell death in the marmoset

The intense angiogenesis characteristic of early corpus luteum development is dependent upon vascular endothelial growth factor (VEGF) as inhibitors of VEGF administered at the peri-ovulatory period suppress endothelial cell proliferation and progesterone secretion. We now report that administration of VEGF Trap, a soluble decoy receptor-based inhibitor, at the mid- or the late luteal phase in the marmoset results in a rapid decline in plasma progesterone. Since vascularisation of the corpus luteum is largely complete by the mid-luteal phase, it suggested that this functional luteolysis involved mechanisms other than inhibition of angiogenesis. A second experiment investigated the role of VEGF in maintaining the integrity of the luteal vasculature and hormone-producing cells. VEGF Trap was administered to marmosets in the mid-luteal phase and ovaries were obtained 1, 2, 4 or 8 days later for localisation of activated caspase-3 staining in the corpus luteum and compared with those obtained 2, 4 and 8 days after administration of control protein. The number of cells with activated caspase-3 staining was significantly increased after administration of VEGF Trap. Dual staining of activated caspase-3 with the endothelial cell marker CD31 showed that at 1 day post-treatment, more than 90% caspase-3-stained cells were vascular endothelium, prior to detection of an increasing incidence in death of hormone-producing cells on days 2 and 4. Staining with CD31 showed that the endothelial cell area was decreased after treatment. By 8 days after treatment, corpora lutea had regressed to varying degrees, while all control corpora lutea remained healthy. These results show that VEGF inhibition in the mid- or the late luteal phase induces functional luteolysis in the marmoset that is associated with premature and selective death of endothelial cells.     

Regulation of endothelial proliferation by the renin-angiotensin system in human umbilical vein endothelial cells

This study was performed in order to evaluate the role of angiotensin II in physiological angiogenesis. Human umbilical vein endothelial cells (HUVEC) were stained for angiotensin II type 1 receptor (AGTR1) immunocytochemically and for gene expression of renin-angiotensin system (RAS) components. The regulation of the angiogenesis-associated genes vascular endothelial growth factor (VEGF) and angiopoietins (ANGPT1 and ANGPT2) were studied using quantitative RT-PCR. Furthermore, we examined the effect of angiotensin II on the proliferation of HUVEC using Ki-67 as well as BrdU immunocytochemistry and investigated whether the administration of the AGTR1 blocker candesartan or the VEGF antagonist FLT1-Fc could suppress the observed angiotensin II-dependent proangiogenic effect. AGTR1 was expressed in HUVEC and the administration of angiotensin II significantly increased the gene expression of VEGF and decreased the gene expression of ANGPT1. Since the expression of ANGPT2 was not affected significantly the ratio of ANGPT1/ANGPT2 was decreased. In addition, a significantly increased endothelial cell proliferation was observed after stimulation with angiotensin II, which was suppressed by the simultaneous administration of candesartan or the VEGF antagonist FLT1-Fc. These results indicate the potential capacity of angiotensin II in influencing angiogenesis by the regulation of angiogenesis-associated genes via AGTR1. Since VEGF blockade opposed the effect of angiotensin II on cell proliferation, it is hypothesised that VEGF mediates the angiotensin II-dependent effect in concert with the changes in angiopoietin expression. This is the first report of the RAS on the regulation of angiogenesis-associated genes in physiology.     

Polysaccharides derived from Lycium barbarum suppress IGF-1-induced angiogenesis via PI3K/HIF-1α/VEGF signalling pathways in MCF-7 cells

Lycium barbarum (LB) is a berry-type fruit. Lycium barbarum polysaccharides (LBPs), derived from LB, has anti-tumour properties and exhibits potent anti-angiogenic effects. The aim of this study was to elucidate possible signal transduction pathways functioning to mediate the breast cancer-suppressive effects of LBPs. Using MCF-7 cells, we determined that a 90 h treatment with 0.50 mg/ml of LBPs resulted in significant inhibition of cell proliferation. Using this same system, we observed that LBPs could also affect insulin-like growth factor (IGF)-1 protein accumulation, suppress phosphatidylinositol 3-kinase (PI3K) activity and phosphorylated-PI3K (p-PI3K) protein levels, inhibit hypoxia-inducible factor-1 (HIF-1α) protein accumulation without altering HIF-1α mRNA levels, and suppress VEGF mRNA expression and protein production. Our results demonstrate that LBPs may inhibit tumour cell growth by suppressing IGF-1-induced angiogenesis via PI3K/HIF-1α/VEGF signalling pathways.     

番茄红素对糖尿病小鼠骨髓内皮祖细胞功能影响及机制

以链脲霉素(streptozotocin,STZ)诱导C57BL/6小鼠作为糖尿病动物模型,探究番茄红素(lycopene,Lyc)对STZ诱导的糖尿病小鼠骨髓内皮祖细胞(endothelial progenitor cells,EPCs)的保护作用,探讨Lyc防治糖尿病血管并发症的潜力。结果表明:糖尿病小鼠外周血EPCs数量减少,骨髓EPCs氧化应激水平增高,血管内皮生长因子(vascular endothelial growth factor,VEGF)表达降低,EPCs衰老严重并伴功能受损。Lyc灌胃处理糖尿病小鼠后,其外周血EPCs数量增加,骨髓EPCs氧化应激得到抑制,VEGF表达增加,EPCs衰老和功能受损程度明显减轻。由此可知,Lyc作为一种食物来源的植物化合物,具有防治糖尿病血管并发症的潜力。     

Localization of mRNA for vascular endothelial growth factor (VEGF), angiopoietins and their receptors during the peri-implantation period and early pregnancy in marmosets (Callithrix jacchus)

Implantation of a blastocyst into a receptive endometrium is a prerequisite for successful pregnancy. Angiogenesis is a key event in this process but the mechanisms by which localized changes in vascular permeability and angiogenesis occur have yet to be elucidated. Vascular endothelial growth factor (VEGF) and its receptors VEGFR-1 and VEGFR-2 have been implicated as key players in vascular remodelling and placentation. Angiopoietins also appear to have a significant role in regulation of blood vessel growth, maturation and regression. The aim of this study was to describe the molecular regulation of angiogenesis in the first month of pregnancy in marmosets and to address the putative physiological roles for these factors. Uteri were studied at weeks 2, 3 and 4 of pregnancy and compared with late secretory non-pregnant endometrium. Implantation in marmosets occurs at day 11 of pregnancy; hence, these time points were chosen so that the peri-implantation period and very early pregnancy could be studied. mRNAs for VEGF, VEGFR-1 and VEGFR-2, angiopoietin 1, angiopoietin 2 and their receptor Tie-2 were localized and quantified by in situ hybridization. Endothelial cells were identified by CD31 immunocytochemistry. VEGF mRNA was present in all compartments except endothelial cells, and its expression generally increased throughout pregnancy except in upper zone glandular epithelium and luminal epithelium, where a decrease in expression was observed. VEGF receptor mRNAs were found in endothelial cells of the upper zones immediately surrounding glandular epithelium. Angiopoietin 1 mRNA was localized to glandular epithelium of the upper and lower zones throughout pregnancy, and increased in stroma at week 4. Expression of angiopoietin 2 mRNA was localized exclusively to endothelial cells of large luminal vessels and was higher in endometrium from marmosets at week 4 of pregnancy than in endometrium from all other stages. These data provide comprehensive evidence that VEGFR-1 and -2, and angiopoietin 1, angiopoietin 2 and Tie-2 interactions may be involved in the preparation of endometrium for implantation, remodelling of the maternal vasculature and trophoblast invasion during the peri-implantation period in this primate species.     

Growth inhibitory efficacy of lycopene and β-carotene against androgen-independent prostate tumor cells xenografted in nude mice

Scope : In this study, we evaluated the efficacy of lycopene against the growth of prostate cancer in vivo. Methods and results : Athymic nude mice were implanted subcutaneously with human androgen‐independent prostate carcinoma PC‐3 cells. They were supplemented with a low or a high dose of lycopene (4 and 16 mg/kg) and a single dose of β‐carotene (16 mg/kg) twice a week for 7 wk. At the end of the experiment, both lycopene and β‐carotene strongly inhibited the tumor growth, as evidenced by the decrease in tumor volume and tumor weight. High‐dosage lycopene and β‐carotene significantly decreased the expression of proliferating cell nuclear antigen in tumor tissues and increased the levels of insulin‐like growth factor‐binding protein‐3 in plasma. In addition, high‐dosage lycopene supplementation significantly decreased the vascular endothelial growth factor (VEGF) levels in plasma. In contrast, β‐carotene supplementation significantly increased the VEGF levels, as compared with tumor control group. Conclusion : Lycopene and β‐carotene supplementation suppressed the growth of prostate tumor cells, and the effects are likely associated with reduction of proliferation (attenuation of proliferating cell nuclear antigen expression) and with interference of the insulin‐like growth factor 1 signaling (increased plasma insulin‐like growth factor‐binding protein‐3 levels). Furthermore, the inhibition of VEGF by lycopene suggests that the antitumor mechanisms of lycopene also involve anti‐angiogenesis.     

苦瓜总皂苷对糖尿病大鼠肾保护作用及其机制研究

探讨苦瓜总皂苷(TSMC)对糖尿病大鼠肾脏保护作用及其作用机制。将Wistar大鼠随机分为4组,A:正常对照组;B:模型组;C:300mg/kg苦瓜总皂苷组;D:100mg/kg苦瓜总皂苷组。灌胃给药每日1次,8周后,检测各组肾组织中空腹血糖、肌酐(Cr)、尿素氮(BUN);放免分析检测血清胰岛素(Ins)、α1微球蛋白(α1-MG)、β2微球蛋白(β2-MG)。RT-PCR检测肾组织血管内皮生长因子(VEGF)水平的变化。与糖尿病组相比,苦瓜总皂苷治疗组肌酐、尿素氮、α1-MG、β2-MG显著降低(P<0.05),VEGF mRNA的表达减弱(P<0.05)。苦瓜总皂苷可显著降低糖尿病大鼠组织VEGF mRNA的表达,改善肾功能,延缓糖尿病肾病发展。     

Fibroblast growth factor 2 is a key determinant of vascular sprouting during bovine luteal angiogenesis

Fibroblast growth factor (FGF) 2 and vascular endothelial growth factor (VEGF) A are thought to be key controllers of luteal angiogenesis; however, their precise roles in the regulation and coordination of this complex process remain unknown. Thus, the temporal and spatial patterns of endothelial network formation were determined by culturing mixed cell types from early bovine corpora lutea on fibronectin in the presence of FGF2 and VEGFA (6 h to 9 days). Endothelial cells, as determined by von Willebrand factor immunohistochemistry, initially grew in cell islands (days 0-3), before undergoing a period of vascular sprouting to display a more tubule-like appearance (days 3-6), and after 9 days in culture had formed extensive intricate networks. Mixed populations of luteal cells were treated with SU1498 (VEGF receptor 2 inhibitor) or SU5402 (FGF receptor 1 inhibitor) or control on days 0-3, 3-6 or 6-9 to determine the role of FGF2 and VEGFA during these specific windows. The total area of endothelial cells was unaffected by SU1498 treatment during any window. In contrast, SU5402 treatment caused maximal reduction in the total area of endothelial cell networks on days 3-6 vs controls (mean reduction 81%; P<0.001) during the period of tubule initiation. Moreover, SU5402 treatment on days 3-6 dramatically reduced the total number of branch points (P<0.001) and degree of branching per endothelial cell island (P<0.05) in the absence of changes in mean island area. This suggests that FGF2 is a key determinant of vascular sprouting and hence critical to luteal development.     

The effects of ergot and non-ergot-derived dopamine agonists in an experimental mouse model of endometriosis

Implantation of a retrogradely shed endometrium during menstruation requires an adequate blood supply, which allows the growth of endometriotic lesions. This suggests that the development of endometriosis can be impaired by inhibiting angiogenesis. The growth of endometriotic foci is impaired by commercial oncological antiangiogenic drugs used to block vascular endothelial growth factor (VEGF) signaling. The dopamine agonist cabergoline (Cb2) inhibits the growth of established endometriosis lesions by exerting antiangiogenic effects through VEGFR2 inactivation. However, the use of ergot-derived Cb2 is associated with an increased incidence of cardiac valve regurgitation. To evaluate the potential usage of non-ergot-derived dopamine agonists for the treatment of human endometriosis, we compared the efficacy of quinagolide with that of Cb2 in preventing angiogenesis and vascularization in a heterologous mouse model of endometriosis. Nude mice whose peritoneum had been implanted with eutopic human endometrial fragments were treated with vehicle, 50 μg/kg per day oral Cb2, or 50 or 200 μg/kg per day quinagolide during a 14-day period. At the end of the treatment period, the implants were excised in order to assess lesion size, cell proliferation, degree of vascularization, and angiogenic gene expression. Neoangiogenesis was inhibited and the size of active endometriotic lesions, cellular proliferation index, and angiogenic gene expression were significantly reduced by both dopamine agonists when compared with the placebo. Given that Cb2 and quinagolide were equally effective in inhibiting angiogenesis and reducing lesion size, these experiments provide the rationale for pilot studies to explore the use of non-ergot-derived dopamine agonists for the treatment of endometriosis in humans.     

Gene expression property of high-density three-dimensional tissue of HepG2 cells formed in radial-flow bioreactor

In our previous study, we examined three-dimensional culture using 5-ml radial-flow bioreactor (RFB) and showed that genes encoding cell cycle related proteins were suppressed in a stable phase. In this study, we analyzed the gene expression profiles of RFB-cultivated HepG2 cells and found that vascular endothelial growth factor (VEGF) production was strongly induced in the stable phase compared with the growth phase or static two-dimensional culture. When human umbilical vein endothelial cells (HUVECs) were grown under the conditioned medium of the stable phase, it was found that the formation of new blood vessels was induced in the angiogenesis model. DNA microarray analysis showed that the expression levels of both genes related to cell cycle arrest and which are known as tumor markers have increased in the stable phase. This result suggests that HepG2 cells in the stable phase maintain an active tumor phenotype. In addition, the expression of genes induced in the hypoxic condition was also induced in the stable phase. When the culture was carried out under a higher dissolved oxygen (DO) concentration, VEGF production did not decrease significantly and the new blood-vessel-forming ability of the conditioned medium was not suppressed. This suggests that the induction of VEGF production in a stable phase is not affected by DO during the tested level. These results suggest that the RFB cell culture system may be used to assess tumor progression mechanism under three-dimensional condition in vitro.     

复方银杏叶对糖尿病大鼠睾丸VEGF的影响

目的:探讨复方银杏叶(CGL)对糖尿病大鼠睾丸VEGF的影响。方法:在40只Wistar雄性大鼠中随机抽取10只作为正常对照组(NC),其余大鼠用链脲佐菌素(Streptozotocin,STZ)加高脂高糖饮食制备2型糖尿病模型。造模动物筛选后,随机分为糖尿病组(DM组)和CGL治疗组,每组10只。治疗组给予CGL10周后,取双侧睾丸组织,提取蛋白,检测组织中血管内皮生长因子(VEGF)含量。结果:2型糖尿病模型制备成功,糖尿病组与对照组比较,VEGF含量降低,差别有显著性意义(P<0.01),而治疗组与糖尿病组比较,VEGF含量升高,差别有显著性意义(P<0.01)。结论:复方银杏叶能够提高糖尿病大鼠睾丸VEGF的表达,对糖尿病伴随生殖功能障碍有一定的改善作用。     

Growth factor/heparin-immobilized collagen gel system enhances viability of transplanted hepatocytes and induces angiogenesis

Hepatocyte transplantation is being explored as a treatment strategy for end-stage liver disease; however, the main limitation is the insufficient vascularization of transplanted hepatocytes. To overcome this problem, a suitable 3D microenvironment and the types of transplanted cells must be considered for hepatocyte transplantation. In this study, a growth factor (GF)/heparin-immobilized collagen gel-filled polyurethane foam (PUF) scaffold was developed for angiogenesis induction and hepatocyte transplantation. First, a vascular endothelial growth factor (VEGF)/heparin-immobilized, collagen-gel-filled PUF scaffold was developed to establish a prevascularized cavity in the subcutaneous space in rats. Second, accompanied by 70% partial hepatectomy (PH), hepatocytes were embedded inside heparin-immobilized, collagen-gel-filled PUF scaffolds, and were transplanted into the VEGF-induced prevascularized cavity. The benefits of using this system were confirmed by using three types of hepatocytes, namely single hepatocyte, hepatocyte spheroids, and fetal hepatocytes. The normalized hemoglobin content and live nucleus numbers were determined separately to evaluate the angiogenesis and viability of transplanted hepatocytes. In summary, after PH pretreatment, transplantation of fetal hepatocyte-embedded, heparin-immobilized, collagen-gel-filled PUF scaffold into a VEGF-induced prevascularized cavity appears to be a promising strategy for future liver tissue engineering.     

Anti-inflammatory Effects of Limonene from Yuzu (Citrus junos Tanaka) Essential Oil on Eosinophils

ABSTRACT: Yuzu (Citrus junos Tanaka) has been used as a traditional medicine in Japan. We investigated in vitro anti-inflammatory effects of limonene from yuzu peel on human eosinophilic leukemia HL-60 clone 15 cells. To examine anti-inflammatory effects of limonene on the cells, we measured the level of reactive oxygen species (ROS), monocyte chemoattractant protein-1 (MCP-1), nuclear factor (NF) kappa B, and p38 mitogen-activated protein kinase (MAPK). We found that low concentration of limonene (7.34 mmol/L) inhibited the production of ROS for eotaxin-stimulated HL-60 clone 15 cells. 14.68 mmol/L concentration of limonene diminished MCP-1 production via NF-kappa B activation comparable to the addition of the proteasomal inhibitor MG132. In addition, it inhibited cell chemotaxis in a p38 MAPK dependent manner similar to the adding of SB203580. These results suggest that limonene may have potential anti-inflammatory efficacy for the treatment of bronchial asthma by inhibiting cytokines, ROS production, and inactivating eosinophil migration.     

Regulation and manipulation of angiogenesis in the primate corpus luteum

Intense physiological angiogenesis occurs during the early stages of luteal development, providing a model in which the complex processes regulating the angiogenic pathway may be studied. Here, a working hypothesis is presented to explain the diverse changes in the vasculature of the corpus luteum that occur over a short period, based around changes in vascular endothelial growth factor, the angiopoietins and matrix metalloproteinases. An illustration is given of how angiogenesis can be monitored in a primate model and how the role of individual angiogenic factors such as vascular endothelial growth factor may be explored in vivo. Because of the marked effect of inhibition of angiogenesis on luteal function, it is predicted that the normal processes of follicular development, ovulation and luteal function could all be profoundly influenced by the manipulation of angiogenesis.