apyrase and Hypoxia

Topics: Adenosine Triphosphate; Anemia, Sickle Cell; Apyrase; Cations; Cells, Cultured; Erythrocytes; Humans; Hydrogen-Ion Concentration; Hypoxia; Probenecid; Reticulocytes; Suramin

Adenosine triphosphate (ATP) is released at a high concentration in the tumor microenvironment. The overexpression of ectonucleotidases in non-small-cell lung cancer (NSCLC), metabolizing ΑΤP to the immunosuppressive adenosine, is studied.. We examined the expression of the ectonucleotidases CD73 and CD39 in NSCLC in parallel with immunological parameters and markers of hypoxia and anaerobic metabolism. In vitro experiments with A549 and H1299 lung cancer cell lines were also conducted.. CD73 and CD39 were not expressed by normal bronchial and alveolar epithelium. In contrast, these were overexpressed by cancer cells, cancer-associated fibroblasts (CAFs), and tumor-infiltrating lymphocytes (TILs). High CD73 cancer cell expression was directly linked with lactate dehydrogenase LDH5 and with hypoxia-inducible factor HIF1α expression by cancer cells. The expression of CD39 by CAFs was directly linked with PD-L1 expression by cancer cells. A significant abundance of FOXP3+ and PD-1+ TILs was noted in tumors with high CD73 and CD39 stroma expression. In in vitro experiments, hypoxia and acidity induced CD73 mRNA and protein levels in cancer cell lines. Exposure of cancer cell lines to adenosine induced the expression of PD-L1 and LDHA mRNA and protein levels.. Ectonucleotidases are up-regulated in cancer cells, CAFs, and TILs in lung tumors. Such overexpression is linked with regulatory TIL-phenotype and PD-L1 up-regulation by cancer cells. Overexpression of LDH5 is up-regulated by adenosine, creating a vicious cycle, as the high amounts of ATP produced by LDH5-mediated anaerobic glycolysis promote the production of adenosine by a tumor microenvironment rich in ectonucleotidases.

Topics: 5'-Nucleotidase; Adenosine; Adult; Aged; Aged, 80 and over; Antigens, CD; Apyrase; B7-H1 Antigen; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Female; Gene Expression Regulation, Neoplastic; Humans; Hypoxia; Immune Tolerance; Lung Neoplasms; Male; Middle Aged

Despite the fact that nucleotides and adenosine help regulate vascular tone through purinergic signaling pathways, little is known regarding their contributions to the pathobiology of pulmonary arterial hypertension, a condition characterized by elevated pulmonary vascular resistance and remodeling. Even less is known about the potential role that alterations in CD39 (ENTPD1), the ectonucleotidase responsible for the conversion of the nucleotides ATP and ADP to AMP, may play in pulmonary arterial hypertension. In this study we identified decreased CD39 expression on the pulmonary endothelium of patients with idiopathic pulmonary arterial hypertension. We next determined the effects of CD39 gene deletion in mice exposed to normoxia or normobaric hypoxia (10% oxygen). Compared with controls, hypoxic CD39(-/-) mice were found to have a markedly elevated ATP-to-adenosine ratio, higher pulmonary arterial pressures, more right ventricular hypertrophy, more arterial medial hypertrophy, and a pro-thrombotic phenotype. In addition, hypoxic CD39(-/-) mice exhibited a marked increase in lung P2X1 receptors. Systemic reconstitution of ATPase and ADPase enzymatic activities through continuous administration of apyrase decreased pulmonary arterial pressures in hypoxic CD39(-/-) mice to levels found in hypoxic CD39(+/+) controls. Treatment with NF279, a potent and selective P2X1 receptor antagonist, lowered pulmonary arterial pressures even further. Our study is the first to implicate decreased CD39 and resultant alterations in circulating purinergic signaling ligands and cognate receptors in the pathobiology of pulmonary arterial hypertension. Reconstitution and receptor blocking experiments suggest that phosphohydrolysis of purinergic nucleotide tri- and diphosphates, or blocking of the P2X1 receptor could serve as treatment for pulmonary arterial hypertension.

Topics: Adenosine; Adenosine Triphosphate; Animals; Antigens, CD; Antihypertensive Agents; Apyrase; Arterial Pressure; Disease Models, Animal; Genetic Predisposition to Disease; Humans; Hydrolysis; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; Lung; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Pulmonary Artery; Purinergic P2X Receptor Antagonists; Receptors, Purinergic P2X1; Severity of Illness Index; Signal Transduction; Suramin; Vascular Remodeling; Ventricular Remodeling

To what extent hypoxia alters the adenosine (ADO) system and impacts on cardiac function during embryogenesis is not known. Ectonucleoside triphosphate diphosphohydrolase (CD39), ecto-5'-nucleotidase (CD73), adenosine kinase (AdK), adenosine deaminase (ADA), equilibrative (ENT1,3,4), and concentrative (CNT3) transporters and ADO receptors A1, A2A, A2B, and A3 constitute the adenosinergic system. During the first 4 days of development chick embryos were exposed in ovo to normoxia followed or not followed by 6 h hypoxia. ADO and glycogen content and mRNA expression of the genes were determined in the atria, ventricle, and outflow tract of the normoxic (N) and hypoxic (H) hearts. Electrocardiogram and ventricular shortening of the N and H hearts were recorded ex vivo throughout anoxia/reoxygenation ± ADO. Under basal conditions, CD39, CD73, ADK, ADA, ENT1,3,4, CNT3, and ADO receptors were differentially expressed in the atria, ventricle, and outflow tract. In H hearts ADO level doubled, glycogen decreased, and mRNA expression of all the investigated genes was downregulated by hypoxia, except for A2A and A3 receptors. The most rapid and marked downregulation was found for ADA in atria. H hearts were arrhythmic and more vulnerable to anoxia-reoxygenation than N hearts. Despite downregulation of the genes, exposure of isolated hearts to ADO 1) preserved glycogen through activation of A1 receptor and Akt-GSK3β-GS pathway, 2) prolonged activity and improved conduction under anoxia, and 3) restored QT interval in H hearts. Thus hypoxia-induced downregulation of the adenosinergic system can be regarded as a coping response, limiting the detrimental accumulation of ADO without interfering with ADO signaling.

Topics: 5'-Nucleotidase; Adaptation, Physiological; Adenosine; Adenosine Kinase; Animals; Antigens, CD; Apyrase; Chick Embryo; Energy Metabolism; Equilibrative Nucleoside Transport Proteins; Gene Expression Regulation, Developmental; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Heart; Hypoxia; Membrane Transport Proteins; Myocardium; Organogenesis; Proto-Oncogene Proteins c-akt; Receptors, Purinergic P1; RNA, Messenger; Signal Transduction; Time Factors

Purinergic signaling plays an important role in inflammation and vascular integrity, but little is known about purinergic mechanisms during the pathogenesis of atherosclerosis in humans.. The objective of this study is to study markers of purinergic signaling in a cohort of patients with peripheral artery disease.. Plasma ATP and ADP levels and serum nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39) and ecto-5'-nucleotidase/CD73 activities were measured in 226 patients with stable peripheral artery disease admitted for nonurgent invasive imaging and treatment. The major findings were that ATP, ADP, and CD73 values were higher in atherosclerotic patients than in controls without clinically evident peripheral artery disease (P<0.0001). Low CD39 activity was associated with disease progression (P=0.01). In multivariable linear regression models, high CD73 activity was associated with chronic hypoxia (P=0.001). Statin use was associated with lower ADP (P=0.041) and tended to associate with higher CD73 (P=0.054), while lower ATP was associated with the use of angiotensin receptor blockers (P=0.015).. Purinergic signaling plays an important role in peripheral artery disease progression. Elevated levels of circulating ATP and ADP are especially associated with atherosclerotic diseases of younger age and smoking. The antithrombotic and anti-inflammatory effects of statins may partly be explained by their ability to lower ADP. We suggest that the prothrombotic nature of smoking could be a cause of elevated ADP, and this may explain why cardiovascular patients who smoke benefit from platelet P2Y12 receptor antagonists more than their nonsmoking peers.

Topics: 5'-Nucleotidase; Adenosine Diphosphate; Adenosine Triphosphate; Adult; Age Factors; Aged; Aged, 80 and over; Alkaline Phosphatase; Angiotensin-Converting Enzyme Inhibitors; Antigens, CD; Apyrase; Artifacts; Atherosclerosis; Biomarkers; Chronic Disease; Comorbidity; Disease Progression; Drug Utilization; Female; Finland; GPI-Linked Proteins; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hypertension; Hypoxia; Male; Middle Aged; Models, Cardiovascular; Peripheral Arterial Disease; Purinergic P2Y Receptor Antagonists; Risk Factors; Second Messenger Systems; Smoking; Thrombophilia

Achieving a prolonged neuroprotective state following transient ischemic attacks (TIAs) is likely to effectively reduce the brain damage and neurological dysfunction associated with recurrent stroke. HPC is a phenomenon in which advanced exposure to mild hypoxia reduces the stroke volume produced by a subsequent TIA. However, this neuroprotection is not long-lasting, with the effects reaching a peak after 3 days. Therefore, in this study, we investigated the use of multiple episodes of hypoxic exposure at different time intervals to induce longer-term protection in a mouse stroke model. C57BL/6 mice were subjected to different hypoxic preconditioning protocols: a single episode of HPC or five identical episodes at intervals of 3 days (E3d HPC) or 6 days (E6d HPC). Three days after the last hypoxic exposure, temporary middle cerebral artery occlusion (MCAO) was induced. The effects of these HPC protocols on hypoxia-inducible factor (HIF) regulated gene mRNA expression were measured by quantitative PCR. Changes in extracellular adenosine concentrations, known to exert neuroprotective effects, were also measured using in vivo microdialysis and high pressure liquid chromatography (HPLC). Neuroprotection was provided by E6d HPC but not E3d HPC. HIF-regulated target gene expression increased significantly following all HPC protocols. However, E3d HPC significantly decreased extracellular adenosine and reduced cerebral blood flow in the ischemic region with upregulated expression of the adenosine transporter, equilibrative nucleoside transporter 1 (ENT1). An ENT1 inhibitor, propentofylline increased the cerebral blood flow and re-established neuroprotection in E3d HPC. Adenosine receptor specific antagonists showed that adenosine mainly through A1 receptor mediates HPC induced neuroprotection. Our data indicate that cooperation of HIF-regulated genes and extracellular adenosine is necessary for HPC-induced neuroprotection.

Topics: 5'-Nucleotidase; Adenosine; Animals; Antigens, CD; Apyrase; Cerebrovascular Circulation; Equilibrative Nucleoside Transport Proteins; Extracellular Space; Hypoxia; Hypoxia-Inducible Factor 1; Ischemic Attack, Transient; Ischemic Preconditioning; Male; Mice; Neurons; Neuroprotective Agents; Receptor, Adenosine A1; Regional Blood Flow; Xanthines

Brain-resident microglia may promote tissue repair following stroke but, like other cells, they are vulnerable to ischemia. Here we identify mechanisms involved in microglial ischemic vulnerability. Using time-lapse imaging of cultured BV2 microglia, we show that simulated ischemia (oxygen-glucose deprivation; OGD) induces BV2 microglial cell death. Removal of extracellular Ca(2+) or application of Brilliant Blue G (BBG), a potent P2X7 receptor (P2X7R) antagonist, protected BV2 microglia from death. To validate and extend these in vitro findings, we assessed parenchymal microglia in freshly isolated hippocampal tissue slices from GFP-reporter mice (CX3CR1(GFP/+)). We confirmed that calcium removal or application of apyrase, an ATP-degrading enzyme, abolished OGD-induced microglial cell death in situ, consistent with involvement of ionotropic purinergic receptors. Indeed, whole cell recordings identified P2X7R-like currents in tissue microglia, and OGD-induced microglial cell death was inhibited by BBG. These pharmacological results were complemented by studies in tissue slices from P2X7R null mice, in which OGD-induced microglia cell death was reduced by nearly half. Together, these results indicate that stroke-like conditions induce calcium-dependent microglial cell death that is mediated in part by P2X7R. This is the first identification of a purinergic receptor regulating microglial survival in living brain tissues. From a therapeutic standpoint, these findings could help direct novel approaches to enhance microglial survival and function following stroke and other neuropathological conditions.

Topics: Animals; Apyrase; Calcium; Cell Death; Cells, Cultured; Extracellular Space; Female; Glucose; Hippocampus; Hypoxia; Ischemia; Male; Membrane Potentials; Mice; Mice, Knockout; Microglia; Purinergic P2X Receptor Antagonists; Receptors, Purinergic P2X7; Rosaniline Dyes

Vascular remodeling plays a pivotal role in a variety of pathophysiological conditions where hypoxia and inflammation are prominent features. Intravascular ATP, ADP and adenosine are known as important regulators of vascular tone, permeability and homeostasis, however contribution of purinergic signalling to endothelial cell growth and angiogenesis remains poorly understood. By using vasa vasorum endothelial cells (VVEC) isolated from pulmonary artery adventitia of control and chronically hypoxic neonatal calves, these studies were aimed to evaluate the effect of hypoxia on biochemical and functional properties of microvascular endothelial network at the sites of angiogenesis. In comparison with normoxic controls, VVEC from hypoxic animals are characterized by (1) drastically impaired nucleoside triphosphate diphosphohydrolase-1 (NTPDase-1/CD39) and ecto-5'-nucleotidase/CD73 activities with respective increases in basal extracellular ATP and ADP levels (2) higher proliferative responses to low micromolar concentrations of ATP and ADP; and (3) enhanced permeability and disordered adenosinergic control of vascular barrier function (measured as a paracellular flux of 70 kDa fluorescein isothiocyanate-dextran). Together, these results suggest that unique pattern of purine-mediated angiogenic activation and enhanced leakiness of VVEC from chronically hypoxic vessels may be defined by disordered endothelial nucleotide homeostasis at sites of active neovascularization.

Topics: 5'-Nucleotidase; Adenosine; Adenosine Diphosphate; Adenosine Triphosphate; Analysis of Variance; Animals; Animals, Newborn; Antigens, CD; Apyrase; Blotting, Western; Capillary Permeability; Cattle; Cell Proliferation; Cyclic AMP; Dextrans; DNA Primers; Endothelial Cells; Fluorescein-5-isothiocyanate; Hypoxia; Neovascularization, Pathologic; Pulmonary Artery; Regression Analysis; Reverse Transcriptase Polymerase Chain Reaction; Vasa Vasorum

Hypoxia is common to several inflammatory diseases, where multiple cell types release adenine-nucleotides (particularly adenosine triphosphate/adenosine diphosphate). Adenosine triphosphate/adenosine diphosphate is metabolized to adenosine through a 2-step enzymatic reaction initiated by CD39 (ectonucleoside-triphosphate-diphosphohydrolase-1). Thus, extracellular adenosine becomes available to regulate multiple inflammatory endpoints. Here, we hypothesized that hypoxia transcriptionally up-regulates CD39 expression. Initial studies revealed hypoxia-dependent increases in CD39 mRNA and immunoreactivity on endothelia. Examination of the human CD39 gene promoter identified a region important in hypoxia inducibility. Multiple levels of analysis, including site-directed mutagenesis, chromatin immunoprecipitation, and inhibition by antisense, revealed a critical role for transcription-factor Sp1 in hypoxia-induction of CD39. Using a combination of cd39(-/-) mice and Sp1 small interfering RNA in in vivo cardiac ischemia models revealed Sp1-mediated induction of cardiac CD39 during myocardial ischemia. In summary, these results identify a novel Sp1-dependent regulatory pathway for CD39 and indicate the likelihood that CD39 is central to protective responses to hypoxia/ischemia.

Topics: Animals; Antigens, CD; Apyrase; Cells, Cultured; Disease Models, Animal; Endothelial Cells; Female; Gene Expression Regulation; Humans; Hypoxia; Male; Mice; Mice, Inbred C57BL; Mutagenesis, Site-Directed; Myocardial Infarction; Myocardial Reperfusion Injury; Promoter Regions, Genetic; RNA, Messenger; RNA, Small Interfering; Sp1 Transcription Factor

Diabetic patients who also have retinitis pigmentosa (RP) appear to have fewer and less severe retinal microvascular lesions. Diabetic retinopathy may be linked to increased inner retinal hypoxia, with the possibility that this is exacerbated by oxygen usage during the dark-adaptation response. Therefore, patients with RP with depleted rod photoreceptors may encounter proportionately less retinal hypoxia, and, when diabetes is also present, there may be fewer retinopathic lesions. This hypothesis was tested in rhodopsin knockout mice (Rho-/-) as an RP model in which the diabetic milieu is superimposed. The study was designed to investigate whether degeneration of the outer retina has any impact on hypoxia, to examine diabetes-related retinal gene expression responses, and to assess lesions of diabetic retinopathy.. Streptozotocin-induced diabetes was created in male C57Bl6 (wild-type; WT) and Rho-/- mice, and hyperglycemia was maintained for 5 months. The extent of diabetes was confirmed by measurement of glycated hemoglobin (%GHb) and accumulation of advanced glycation end products (AGEs). Retinal hypoxia was assessed using the bioreductive drug pimonidazole. The retinal microvasculature was studied in retinal flatmounts stained by the ADPase reaction, and the outer retina was evaluated histologically in paraffin-embedded sections. Retinal gene expression of VEGF-A, TNF-alpha, and mRNAs encoding basement membrane component proteins were quantified by real-time RT-PCR.. The percentage GHb increased significantly in the presence of diabetes (P < 0.001) and was not different between WT or Rho-/- mice. Hypoxia increased in the retina of WT diabetic animals when compared with controls (P < 0.001) but this diabetes-induced change was absent in Rho-/- mice. Retinal gene expression of VEGF-A was significantly increased in WT mice with diabetes (P < 0.05), but was unchanged in Rho-/- mice. TNF-alpha gene expression significantly increased (4.9-fold) in WT mice with diabetes (P < 0.05) and also increased appreciably in Rho-/- mice but to a reduced extent (1.5 fold; P < 0.05). The outer nuclear layer in nondiabetic Rho-/- mice was reduced to a single layer after 6 months, but when diabetes was superimposed on this model, there was less degeneration of photoreceptors (P < 0.05). Vascular density was attenuated in diabetic WT mice compared with the nondiabetic control (P < 0.001); however, this diabetes-related disease was not observed in Rho-/- mice.. Loss of the outer retina reduces the severity of diabetic retinopathy in a murine model. Oxygen usage by the photoreceptors during dark adaptation may contribute to retinal hypoxia and exacerbate the progression of diabetic retinopathy.

Topics: Animals; Animals, Genetically Modified; Apyrase; Basement Membrane; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Enzyme-Linked Immunosorbent Assay; Glycated Hemoglobin; Glycation End Products, Advanced; Histocytochemistry; Hypoxia; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Retinal Vessels; Retinitis Pigmentosa; Reverse Transcriptase Polymerase Chain Reaction; Rhodopsin; RNA, Messenger; Tumor Necrosis Factor-alpha; Vascular Endothelial Growth Factor A

This study was conducted to evaluate whether regions of the retinal neuropile become hypoxic during periods of high oxygen consumption and whether depletion of the outer retina reduces hypoxia and related changes in gene expression.. Retinas from rhodopsin knockout (Rho-/-) mice were evaluated along with those of wild-type (WT) control animals. Retinas were also examined at the end of 12-hour dark or light periods, and a separate group was treated with l-cis-diltiazem at the beginning of a 12-hour dark period. Hypoxia was assessed by deposition of hypoxyprobe (HP) and HP-protein adducts were localized by immunohistochemistry and quantified using ELISA. Also, hypoxia-regulated gene expression and transcriptional activity were assessed alongside vascular density.. Hypoxia was observed in the inner nuclear and ganglion cell layers in WT retina and was significantly reduced in Rho-/- mice (P < 0.05). Retinal hypoxia was significantly increased during dark adaptation in WT mice (P < 0.05), whereas no change was observed in Rho-/- or with l-cis-diltiazem-treated WT mice. Hypoxia-inducible factor (HIF)-1alpha DNA-binding and VEGF mRNA expression in Rho-/- retina was significantly reduced in unison with outer retinal depletion (P < 0.05). Retina from the Rho-/- mice displayed an extensive intraretinal vascular network after 6 months, although there was evidence that capillary density was depleted in comparison with that in WT retinas.. Relative hypoxia occurs in the inner retina especially during dark adaptation. Photoreceptor loss reduces retinal oxygen usage and hypoxia which corresponds with attenuation of the retinal microvasculature. These studies suggest that in normal physiological conditions and diurnal cycles the adult retina exists in a state of borderline hypoxia, making this tissue particularly susceptible to even subtle reductions in perfusion.

Topics: Animals; Apyrase; Cyclic Nucleotide Phosphodiesterases, Type 6; Dark Adaptation; Diltiazem; Enzyme-Linked Immunosorbent Assay; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Light; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitroimidazoles; Oxygen Consumption; Phosphoric Diester Hydrolases; Retinal Degeneration; Retinal Rod Photoreceptor Cells; Retinal Vessels; Reverse Transcriptase Polymerase Chain Reaction; Rhodopsin; RNA, Messenger; Transcriptional Activation; Vascular Endothelial Growth Factor A

To test the hypothesis that retinal hypoxia is present during vascular development in normal rat pups and in a newborn rat model of retinopathy of prematurity (ROP).. Preretinal vitreous PO(2) measurements were made during room air breathing using (19)F magnetic resonance spectroscopy (MRS) and a perfluoro-15-crown-5-ether droplet in normal adult and newborn (postnatal day [P]1-P20) rats, and in newborn rats exposed first to 14 days of variable oxygen (before NV) and six additional days in room air after variable oxygen exposure (during NV). After each experiment, blood gas values were measured, and retinas were isolated. Retinas were adenosine diphosphatase (ADPase) stained, and flatmounted to determine peripheral avascular extent and NV incidence and severity.. In the vascularized rat retina, no significant difference (P > 0.05) was found between the droplet-derived preretinal vitreous oxygen tension (24 +/- 2 mm Hg, mean +/- SEM, n = 18) and previously reported electrode-measured oxygen tension (22 +/- 1 mm Hg). Only during normal retinal vessel growth (P1-P10) and before the appearance of NV was evidence for retinal hypoxia found at the border of the vascular and avascular retina. However, the mean PO(2) (range, 24-28 mm Hg) over the vascular retina was not different (P > 0.05) between any of the newborn rat groups in this study.. (19)F MRS of a perfluorocarbon droplet provides an accurate measure of preretinal vitreous oxygen tension in rats. These data support an important role of physiologic hypoxia in normal retinal circulatory development and raises the possibility that, in experimental ROP, retinal hypoxia is a necessary but not sufficient condition for the development of retinal NV.

Topics: Animals; Animals, Newborn; Apyrase; Crown Ethers; Disease Models, Animal; Ethers, Cyclic; Female; Humans; Hypoxia; Infant, Newborn; Magnetic Resonance Imaging; Male; Oxygen; Rats; Rats, Sprague-Dawley; Retinal Neovascularization; Retinal Vessels; Retinopathy of Prematurity

Loss of retinal capillaries is an inherent component of late stage autosomal dominant retinitis pigmentosa (ADRP). This study examined the hypothetical role of tissue hyperoxia in this vascular attenuation process and tested the potential of ambient hypoxia to reverse it.. Transgenic mice expressing a mutant opsin gene with a 3-bp deletion of isoleucine at codon 255/256 were used. This model is characterized by early onset of a rapidly progressing retinal degeneration that by postnatal day (P)20 results in the loss of all but one row of photoreceptor nuclei. At P20 some mice were placed in 12% oxygen until they were euthanatized at P26. The remainder were maintained in normoxia and killed at the same age. Retinas were dissected, stained for ADPase, and flat-mounted.. Deep plexus capillary density was significantly different in normoxic normals versus transgenics at 20 days of age (P:

Topics: Animals; Apyrase; Atrophy; Capillaries; Cell Death; Disease Models, Animal; Female; Hypoxia; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Photoreceptor Cells, Vertebrate; Retinal Vessels; Retinitis Pigmentosa; Rod Opsins

To determine whether the retina is hypoxic in early stages of diabetic retinopathy in cats and to correlate intraretinal PO2 with fluorescein angiographic and histologic alterations.. Intraretinal PO2 was measured with microelectrodes in three cats with long-standing diabetes (>6 years) that had been followed with fluorescein angiographs every 6 months. Average PO2 in the inner vascularized half of the retina was compared with similar measurements in 21 control animals. Photoreceptor oxygen consumption was also compared. The retinal vascular endothelium of the diabetic animals was stained for ADPase activity in flatmounts, and transverse sections were used to visualize microscopic alterations in vascular structure.. PO2 in the inner half of the retina was abnormally low in the diabetic cats, 7.7+/-5.2 mm Hg (35 penetrations in 3 cats) versus 16.4+/-9.3 mm Hg in normal cats (85 penetrations in 21 cats) (P << 0.001). Oxygenation was almost normal in some regions of the diabetic retinas, but little evidence of oxygen supply from the retinal circulation was observed in other regions. Inner retinal hypoxia was present in areas with no detectable capillary dropout in fluorescein angiograms or flatmounts. The worst changes histologically were microaneurysms, leukocyte and platelet plugging of aneurysms and venules, and degenerating endothelial cells in capillary walls. These histologic abnormalities were confined to small regions, some of which could be positively correlated with markedly abnormal PO2 profiles. Photoreceptor oxygen utilization was not affected in two diabetic cats, but was below normal in one animal in which choroidal PO2 was low.. This is the first direct demonstration of retinal hypoxia in early diabetic retinopathy, before capillary dropout was evident clinically. Hypoxia was correlated with endothelial cell death, leukocyte plugging of vessels, and microaneurysms.

Topics: Animals; Apyrase; Cats; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Endothelium, Vascular; Fluorescein Angiography; Hypoxia; Microelectrodes; Oxygen; Oxygen Consumption; Pancreatectomy; Photoreceptor Cells; Retinal Vessels