Measurement of retinal blood flow rate in diabetic rats: disparity between techniques due to redistribution of flow

PURPOSE

Reports of altered retinal blood flow in experimental models of type I diabetes have provided contrasting results, which leads to some confusion as to whether flow is increased or decreased. The purpose of our study was to evaluate early diabetes-induced changes in retinal blood flow in diabetic rats, using two distinctly different methods.

METHODS

Diabetes was induced by injection of streptozotocin (STZ), and retinal blood flow rate was measured under anesthesia by a microsphere infusion technique, or by an index of flow based on the mean circulation time between arterioles and venules. Measurements in STZ rats were compared to age-matched nondiabetic controls. In addition, the retinal distribution of fluorescently-labeled red blood cells (RBCs) was viewed by confocal microscopy in excised flat mounts.

RESULTS

Retinal blood flow rate was found to decrease by approximately 33% in the STZ rats compared to controls (P < 0.001) as assessed by the microsphere technique. However, in striking contrast, the mean circulation time through the retina was found to be almost 3× faster in the STZ rats (P < 0.01). This contradiction could be explained by flow redistribution through the superficial vessels of the diabetic retina, with this possibility supported by our observation of significantly fewer RBCs flowing through the deeper capillaries.

CONCLUSIONS

We conclude that retinal blood flow rate is reduced significantly in the diabetic rat, with a substantial decrease of flow through the capillaries due to shunting of blood through the superficial layer, allowing rapid transit from arterioles to venules.

Retinal blood flow abnormalities following six months of hyperglycemia in the Ins2(Akita) mouse

The aim of this study was to characterize the microvascular flow abnormalities and oxygenation changes that are present following six months of hyperglycemia in the diabetic Ins2(Akita) mouse. Previous studies have shown decreased retinal blood flow in the first several weeks of hyperglycemia in rodents, similar to the decreases seen in the early stages of human diabetes. However, whether this alteration in the mouse retina continues beyond the initial weeks of diabetes has yet to be determined, as are the potential consequences of the decreased flow on retinal oxygenation. In this study, male Ins2(Akita) and age-matched C57BL/6 (non-diabetic) mice were maintained for a period of six months, at which time intravital microscopy was used to measure retinal blood vessel diameters, blood cell velocity, vascular wall shear rates, blood flow rates, and transient capillary occlusions. In addition, the presence of hypoxia was assessed using the oxygen-sensitive probe pimonidazole. The diabetic retinal microvasculature displayed decreases in red blood cell velocity (30%, p<0.001), shear rate (25%, p<0.01), and flow rate (40%, p<0.001). Moreover, transient capillary stoppages in flow were observed in the diabetic mice, but rarely in the non-diabetic mice. However, no alterations were observed in retinal hypoxia as determined by a pimonidazole assay, suggesting the possibility that the decreases seen in retinal blood flow may be dictated by a decrease in retinal oxygen utilization.

Influence of glutathione on the electroretinogram in diabetic and non-diabetic rats

AIMS

The purpose of this study was to investigate the influence of glutathione on the electroretinogram (ERG) in diabetic and non-diabetic rats.

MATERIALS AND METHODS

Streptozotocin (STZ: 60 mg/kg) was injected into male RCC Wistar rats to induce hyperglycemia, with buffer instead of STZ injected into age-matched non-diabetic controls. After 8 weeks, ERG measurements were obtained at seven different scotopic flash intensities on the two groups of anesthetized, dark-adapted rats (controls, STZ). Following ERG measurements, eyes were enucleated for measurements of retinal/vitreous GSH and glutathione disulfide (GSSG).

RESULTS

Diabetic rats produced delayed b-wave ERG signals (increased implicit times), but had normal a-wave and b-wave amplitudes, a-wave implicit times, and oscillatory potentials. No differences were observed in retinal GSH or GSSG between controls and diabetics; however, correlations between GSH and all ERG parameters (with the exception of b-wave implicit times) were noted, and were not significantly altered by the presence of hyperglycemia.

CONCLUSIONS

GSH is likely to play an important role in retinal function as assessed by the ERG, with this role not substantially altered in rats diabetic for 8 weeks.

Effect of tempol on diabetes-induced decreases in retinal blood flow in the mouse

PURPOSE

The purpose was to investigate the effect of the superoxide dismutase mimetic tempol on decreases in retinal blood flow that are found in diabetic mice.

MATERIALS AND METHODS

Streptozotocin (STZ) was injected into male C57BL/6 mice to induce hyperglycemia. One week following the STZ injection, subsets of the mice were given drinking water with or without 1 mM tempol for an additional three weeks. At the end of the four-week protocol, microvascular parameters were quantified via intravital microscopy, and included measurements of retinal diameters, red blood cell (RBC) velocities, blood flow rates, and wall shear rates.

RESULTS

Diabetes induced ~40-45% decreases in retinal blood flow rate (p < 0.001) four weeks following injection of STZ. The decrease in blood flow rate occurred with decreases in microvascular diameters (D) and RBC velocities (V). The average percentage decrease in velocity was greater than the percentage decrease in diameter and, therefore, wall shear rates (= 8 V/D) were ~25% lower in the diabetics than in the non-diabetics (p < 0.05). A three-week administration of tempol in the STZ mice allowed significantly higher blood flow rates than in the untreated STZ mice, with RBC velocities improved by the antioxidant (p < 0.05 on the venular side). However, tempol provided only moderate (and not statistically significant) improvements in wall shear rates.

CONCLUSIONS

The antioxidant tempol provides partial improvements in retinal microvascular hemodynamics early in the progression of STZ-induced diabetes in mice.

Relationship among circulating leukocytes, platelets, and microvascular responses during induction of chronic colitis

The mechanisms by which microvascular alterations contribute to the pathogenesis of the inflammatory bowel diseases (IBDs; Crohn's disease, ulcerative colitis) have not been clearly delineated. The purpose of the current study was to characterize the inflammatory events, microvascular alterations, and blood cell changes that occur in a mouse model of IBD. In this model, CD4(+) T-lymphocytes obtained from interleukin-10-deficient mice were injected intraperitoneally into lymphopenic, recombinase-activating gene-1 deficient (RAG(-/-)) mice. Two groups of control mice were also included: RAG(-/-) mice and C57BL/6 mice that were injected with phosphate-buffered saline but did not receive the T-cells. Four weeks later, the RAG(-/-) mice that had received the T-cell transfer showed significant signs of colonic inflammation, but without significant decreases in either body weight or mean arterial blood pressure. T-cell transfer increased the volume % of circulating platelets, while decreasing the number of circulating red blood cells. Additionally, the T-cell transfer tended to increase the circulating numbers of both lymphocytes and neutrophils when compared to unmanipulated RAG(-/-) mice. First-order colonic arterioles and venules tended to dilate in the colitic mice; however, the dilation was considerably more substantial with higher numbers of circulating leukocytes. The possibility that circulating inflammatory cells initiate the microvascular alterations in colitis warrants further investigation.

Inhibition of 20-HETE attenuates diabetes-induced decreases in retinal hemodynamics

The mechanisms of early diabetes-induced decreases in retinal blood flow have yet to be fully determined. The aim of this study was to explore the hypothesis that 20-hydroxyeicosatetraenoic acid (20-HETE) plays a role in the early decrease of retinal hemodynamics in diabetic mice. 20-HETE has been implicated previously in the diabetes-enhanced vasoconstriction of mesenteric and renal vessels; however, its role in the diabetic retinal microcirculation has not been investigated. Diabetes was induced by multiple low-dose injections of streptozotocin (STZ; 50 mg/kg for 5 consecutive days), then ∼2 weeks later the mice were administered daily intraperitoneal injections with or without the 20-HETE inhibitor HET0016 (2.5 mg/kg/day) for the following 2 weeks. Non-diabetic age-matched mice were included as controls. Intravital microscopy was used to obtain measurements of retinal vascular diameters and red blood cell (RBC) velocities for the feed arterioles and draining venules extending out of and into the optic disk. From these values, wall shear rates and blood flow rates were calculated. Diabetes induced approximately 30-40% decreases in RBC velocity, wall shear rate, and blood flow rate. These decreases were attenuated to 5-10% in the mice given HET0016. In summary, the 20-HETE inhibitor HET0016 is able to attenuate the retinal hemodynamic changes induced by diabetes.

Relationship between inflammation and tissue hypoxia in a mouse model of chronic colitis

BACKGROUND

Hypoxia has been reported to be associated with the colonic inflammation observed in a chemically induced mouse model of self-limiting colitis, suggesting that low tissue oxygen tension may play a role in the pathophysiology of inflammatory tissue injury. However, no studies have been reported evaluating whether tissue hypoxia is associated with chronic gut inflammation. Therefore, the objective of the present study was to determine whether hypoxia is produced within the colon during the development of chronic gut inflammation.

METHODS

Adoptive transfer of CD4(+) T cells obtained from interleukin-10-deficient (IL-10(-/-)) mice into lymphopenic recombinase-activating gene-1-deficient (RAG(-/-)) mice induces chronic colonic inflammation, with the inflammation ranging from mild to severe as determined by blinded histological analyses. Colonic blood flow, hematocrit, and vascular density were determined using standard protocols, whereas tissue hypoxia was determined using the oxygen-dependent probe pimonidazole.

RESULTS

Adoptive transfer of IL-10(-/-) CD4(+) T cells into RAG(-/-) recipients induced chronic colonic inflammation that ranged from mild to severe at 8 weeks following T-cell transfer. The colitis was characterized by bowel wall thickening, goblet cell dropout, and inflammatory infiltrate. Surprisingly, we found that animals exhibiting mild colonic inflammation had increased hypoxia and decreased systemic hematocrit, whereas mice with severe colitis exhibited levels of hypoxia and hematocrit similar to healthy controls. In addition, we observed that the extent of hypoxia correlated inversely with hematocrit and vascular density.

CONCLUSIONS

Changes in hematocrit, vascular density, and inflammatory state appear to influence the extent of tissue oxygenation in the T-cell-mediated model of chronic gut inflammation.

HeLa cell transfection using a novel sonoporation system

Sonoporation has been shown to have an important role in biotechnology for gene therapy and drug delivery. This paper presents a novel microfluidic sonoporation system that achieves high rates of cell transfection and cell viability by operating the sonoporation chamber at resonance. The paper presents a theoretical analysis of the resonant sonoporation chamber design, which achieves sonoporation by forming an ultrasonic standing wave across the chamber. A piezoelectric transducer (PZT 26) is used to generate the ultrasound and the different material thicknesses have been identified to give a chamber resonance at 980 kHz. The efficiency of the sonoporation system was determined experimentally under a range of sonoporation conditions and different exposures time (5, 10, 15, and 20 s, respectively) using HeLa cells and plasmid (peGFP-N1). The experimental results achieve a cell transfection efficiency of 68.9% (analysis of variance, ANOVA, p < 0.05) at the resonant frequency of 980 kHz at 100 V(p-p) (19.5 MPa) with a cell viability of 77% after 10 s of insonication.

Attenuation of streptozotocin-induced microvascular changes in the mouse retina with the endothelin receptor A antagonist atrasentan

Hyperglycemia mediates endothelial cell dysfunction through a number of potential mechanisms that could result in the decrease of retinal blood flow early in diabetes. The aim of this study was to explore the role of endothelin receptor A (ET(A)) in the early decrease of retinal blood flow in diabetic mice. Diabetes was induced by streptozotocin, then ∼1 wk later the mice were administered drinking water with or without the ET(A) receptor antagonist atrasentan (7.5mg/kg/day) for the following 3 weeks. Non-diabetic age-matched mice with or without atrasentan were included as controls. For each mouse, measurements of retinal vascular diameters and red blood cell (RBC) velocities were obtained via intravital microscopy for the 5-7 feed arterioles (and draining venules) extending out of (and into) the optic disk, and from these values, flow rates and wall shear rates were calculated. Additionally, the number of retinal capillaries was counted by fluorescent immunostaining of platelet-endothelial cell adhesion molecule-1 (PECAM-1). Diabetes induced statistically significant decreases in RBC velocity, flow rate, and wall shear rate, with these alterations partially inhibited by atrasentan. No changes were observed in PECAM-1 expression among groups. The changes induced by diabetes, and the attenuation provided by atrasentan, were greater in the smaller retinal arterioles. In summary, ET(A) appears to play a role in the early decreases in retinal blood flow in a mouse model of diabetes.

Association between blood flow and inflammatory state in a T-cell transfer model of inflammatory bowel disease in mice

BACKGROUND

Adoptive transfer of naive T-lymphocyte subsets into lymphopenic mice initiates chronic gut inflammation that mimics several aspects of inflammatory bowel disease (IBD). Patients with IBD can have profound alterations in intestinal blood flow, but whether the same is true in the T-cell transfer model has yet to be determined.

METHODS

In the current study, chronic intestinal inflammation was induced in recombinase-activating gene-1-deficient (RAG(-/-)) mice by adoptive transfer of CD4(+) T-lymphocytes obtained from interleukin-10 deficient (IL-10(-/-)) mice.

RESULTS

Four weeks later, widespread colonic inflammation was observed in the reconstituted recipients, in contrast to 2 control sets of mice injected with a different subset of lymphocytes or with vehicle alone. We observed that the resulting pathology induced in the reconstituted RAG(-/-) mice was divided distinctly into 2 subsets: 1 with blood flow near normal with very high inflammation scores, and the other with severely attenuated blood flow but with much lower signs of inflammation. Colonic and ileal blood flow rates in the latter subset of CD4(+) mice averaged only approximately 30% compared to the mice with higher inflammation scores. The lower blood flow rates were associated with greatly reduced red blood cell concentrations in the tissue, suggesting a possible loss of vascular density.

CONCLUSIONS

In this model of chronic intestinal inflammation, mild inflammation was associated with significant decreases in blood flow.

Multi-modal particle manipulator to enhance bead-based bioassays

By sequentially pushing micro-beads towards and away from a sensing surface, we show that ultrasonic radiation forces can be used to enhance the interaction between a functionalised glass surface and polystyrene micro-beads, and identify those that bind to the surface by illuminating bound beads using an evanescent field generated by guided light. The movement towards and immobilisation of streptavidin coated beads onto a biotin functionalised waveguide surface is achieved by using a quarter-wavelength mode pushing beads onto the surface, while the removal of non-specifically bound beads uses a second quarter-wavelength mode which exhibits a kinetic energy maximum at the boundary between the carrier layer and fluid, drawing beads towards this surface. This has been achieved using a multi-modal acoustic device which exhibits both of these quarter-wavelength resonances. Both 1-D acoustic modelling and finite element analysis has been used to design this device and to investigate the spatial uniformity of the field. We demonstrate experimentally that 90% of specifically bound beads remain attached after applying ultrasound, with 80% of non-specifically bound control beads being successfully removed acoustically. This approach overcomes problems associated with lengthy sedimentation processes used for bead-based bioassays and surface (electrostatic) forces, which delay or prevent immobilisation. We explain the potential of this technique in the development of DNA and protein assays in terms of detection speed and multiplexing.

Hypoxia and the expression of HIF-1alpha and HIF-2alpha in the retina of streptozotocin-injected mice and rats

Decreases in retinal blood flow in diabetics could render the retina hypoxic. In mouse and rat models of diabetes, a decrease in retinal blood flow occurs early, within 3-4 weeks of the induction of hyperglycemia, although information is scarce on whether this early decrease in flow induces hypoxia. The purpose of the current study was to determine whether hypoxia-inducible factor (HIF) levels increase following 4 and/or 12 weeks of hyperglycemia in streptozotocin (STZ)-injected mouse (C57BL/6) and rat (Wistar) retinas. Additionally, retinal tissue hypoxia was measured with pimonidazole following 12 weeks of hyperglycemia. These aims were accomplished via immunostaining of cross-sections from enucleated eyes. In mice, staining for HIF-1alpha and HIF-2alpha showed a contrasting pattern, with HIF-1alpha higher in the inner retina than outer, but HIF-2alpha higher in the outer retina than inner. However, in rats, staining for both HIF-1alpha and HIF-2alpha was more intense in the inner retina. The HIF-1alpha staining intensities and patterns were similar between diabetic animals and their non-diabetic counterparts following 4 and 12 weeks of hyperglycemia. The same was true for HIF-2alpha except for a trend toward an increase following 12 weeks of hyperglycemia in mice. Pimonidazole staining showed significant decreases throughout all layers of the central retina and most layers of the peripheral retina of rats (but not mice), following 12 weeks of hyperglycemia. In summary, despite early decreases in flow in rats and mice, retinal HIF-1alpha and HIF-2alpha were not found to be increased, and the extent of hypoxia may even decrease after 12 weeks of hyperglycemia in rats.

Robust acoustic particle manipulation: A thin-reflector design for moving particles to a surface

Existing ultrasonic manipulation devices capable of pushing particles to a surface ("quarter-wave" devices) have significant potential in sensor applications. A configuration for achieving this that uses the first thickness resonance of a layered structure with both a thin reflector layer and thin-fluid layer is described here. Crucially, this mode is efficient with lossy reflector materials such as polymers, produces a more uniform acoustic radiation force at the reflector, and is less sensitive to geometric variations than previously described quarter-wave devices. This design is thus expected to be suitable for mass produced, disposable devices.

Effects of the endothelin-converting enzyme inhibitor SM-19712 in a mouse model of dextran sodium sulfate-induced colitis

BACKGROUND

Ingestion by mice of dextran sodium sulfate (DSS) induces colonic vasoconstriction and inflammation, with some of the effects potentially mediated by the vasoconstrictor endothelin-1 (ET-1).

METHODS

In this study, mice given 5% 40 kD DSS for 5-6 days had elevated colonic immunostaining for ET-1 and platelet endothelial cell adhesion molecule-1 (PECAM-1). Increased ET-1 can induce microvascular constriction; however, the increase in PECAM-1 is consistent with angiogenesis that could decrease flow resistance.

RESULTS

Our measurements of intestinal blood flow, via infused microspheres, suggests that these 2 factors may offset each other, with only a nonsignificant tendency for a DSS-induced decrease in flow. Daily administration of the endothelin converting enzyme inhibitor SM-19712 (15 mg/kg) attenuated DSS-induced increases in colonic immunostaining of ET-1 and PECAM-1.

CONCLUSIONS

SM-19712 attenuated histologic signs of tissue injury and inflammation induced by DSS, and decreased the extent of loose stools and fecal blood. However, the inhibitor did not significantly decrease DSS-induced colon shortening or tissue levels of myeloperoxidase (an indicator of neutrophil infiltration).

Expression of thromboxane synthase and the thromboxane-prostanoid receptor in the mouse and rat retina

Experimental models of the diabetic retina have suggested a pathological role for thromboxane. To date however, little information is available as to the cellular locations of retinal thromboxane synthase (TxS), or its receptor, even in non-diabetic controls. In this study, C57BL/6 mice and Wistar rats were injected with streptozotocin to induce diabetes, or with buffer for non-diabetic controls. Four weeks following the injection, eyes were enucleated and labeled for TxS and the thromboxane-prostanoid (TP) receptor. Immunofluorescent intensity was quantified in the ganglion cell plus inner plexiform layers, inner nuclear layer, outer plexiform layer, outer nuclear layer, and photoreceptor inner segment. Even in control mice and rats, all layers of the retina showed immunoreactivity for TxS and the TP receptor: however, the pattern of expression demonstrated an inverse relationship, with the highest TxS staining in the inner retina, and the highest TP receptor staining in the outer retina (more specifically, in the photoreceptor inner segment). Four weeks of hyperglycemia did not increase the retinal levels of TxS or TP receptor; however, TP receptor intensities in the outer retina of diabetic rats were highly variable (mostly high but some low), with no values from the photoreceptor inner segment in the same range as obtained from controls.

Altered microvascular hemodynamics during the induction and perpetuation of chronic gut inflammation

Adoptive transfer of naïve CD4+ T cells into lymphopenic mice induces chronic small and large bowel inflammation similar to Crohn's disease. Although much is now known regarding the immunopathology in this model of inflammatory bowel disease, virtually nothing is known about the microvascular hemodynamic changes during the induction and perpetuation of chronic gut inflammation. In this study, CD4+CD45RBhigh T cells obtained from healthy C57BL/6 donor mice were transferred into lymphopenic recombinase-activating gene-1-deficient (RAG knockout) mice, which induced small and large bowel inflammation. At various time points following reconstitution (3 days-9 wk), intravital microscopy was used to examine the microvessels in the submucosa of the ileum and proximal colon following infusion of fluorescently labeled platelets and injection of rhodamine 6G (to label leukocytes). Hemodynamic measurements and the extent of blood cell adhesion to the venular wall were compared with measurements in unreconstituted RAG knockout controls. In <1 wk following reconstitution, velocity and wall shear rate of the arterioles decreased by >50% compared with controls, with this decrease also observed at 4-5 and 7-9 wk postreconstitution. At 7-9 wk, arteriolar diameters were found to be approximately 15% larger than in controls, but, despite this dilation, flow rates in the individual vessels were decreased by approximately 30%. Venular platelet and leukocyte adherence were not significantly elevated above controls; however, an association was found between platelet adherence and venular shear rate. In summary, significant decreases in arteriolar velocity and shear rates are observed in this model of chronic gut inflammation.

Performance of a quarter-wavelength particle concentrator

A series of devices have been investigated which use acoustic radiation forces to concentrate micron sized particles. These multi-layered resonators use a quarter-wavelength resonance in order to position an acoustic pressure node close to the top surface of a fluid layer such that particles migrate towards this surface. As flow-through devices, it is then possible to collect a concentrate of particulates by drawing off the particle stream and separating it from the clarified fluid and so can operate continuously as opposed to batch processes such as centrifugation. The methods of construction are described which include a micro-fabricated, wet-etched device and a modular device fabricated using a micro-mill. These use silicon and macor, a machinable glass ceramic, as a carrier layer between the transducer and fluid channel, respectively. Simulations using an acoustic impedance transfer model are used to determine the influence of various design parameters on the acoustic energy density within the fluid layer and the nodal position. Concentration tests have shown up to 4.4-, 6.0- and 3.2-fold increases in concentration for 9, 3 and 1 microm diameter polystyrene particles, respectively. The effect of voltage and fluid flow rates on concentration performance is investigated and helps demonstrate the various factors which determine the increase in concentration possible.

Attenuation of diabetes-induced retinal vasoconstriction by a thromboxane receptor antagonist

Retinal blood flow has been reported to decrease early in human diabetes as well as in diabetic animal models. The purpose of the present study is to investigate the role of thromboxane receptor binding in the decrease of flow. C57BL/6 mice were injected with streptozotocin (STZ) at 11-12 weeks of age and remained hyperglycemic for 4 weeks. The mice were treated with a selective thromboxane receptor antagonist, GR32191B (vapiprost), in drinking water for the final three weeks at a dose of 1mg/kg/day. In separate experiments, vapiprost was administered only once, as an acute injection 25min prior to the experimental measurements. The measurements included retinal arteriolar and venular diameters and red blood cell (RBC) velocities, from which retinal blood flow was calculated. STZ induced decreases in vascular diameters and RBC velocities, resulting in an approximate 30% decrease in overall retinal blood flow. However, these decreases were not seen in mice given the three-week administration of vapiprost. Acute administration to diabetic mice of 1mg/kg vapiprost, but not 0.1mg/kg, induced arteriolar vasodilation, with the dilation more substantial in smaller feed arterioles. In summary, STZ-induced decreases in retinal blood flow can be attenuated by the thromboxane receptor antagonist vapiprost.

Losartan and ozagrel reverse retinal arteriolar constriction in non-obese diabetic mice

OBJECTIVE

Reductions in retinal blood flow are observed early in diabetes. Venules may influence arteriolar constriction and flow; therefore, we hypothesized that diabetes would induce the constriction of arterioles that are in close proximity to venules, with the constriction mediated by thromboxane and angiotensin II.

METHODS

Using nonobese diabetic (NOD) mice, retinal measurements were performed three weeks following the age at which glucose levels exceeded 200 mg/dL, with accompanying experiments on age-matched normoglycemic NOD mice. The measurements included retinal arteriolar diameters and red blood cell velocities and were repeated following an injection of the thromboxane synthase inhibitor, ozagrel. Mice were subdivided into equal groups and given drinking water with or without the angiotensin II receptor antagonist, losartan.

RESULTS

Retinal arterioles were constricted in hyperglycemic mice, with a significant reduction in flow. However, not all arterioles were equally affected; the vasoconstriction was limited to arterioles that were in closer proximity to venules. The arteriolar vasoconstriction (mean arteriolar diameters = 51 +/- 1 vs. 61 +/- 1 microm in controls; p < 0.01) was eliminated by both ozagrel (61 +/- 2 microm) and losartan (63 +/- 2 microm).

CONCLUSIONS

Venule-dependent arteriolar vasoconstriction in NOD mice is mediated by thromboxane and/or angiotensin II.

Ozagrel reverses streptozotocin-induced constriction of arterioles in rat retina

Retinal blood flow decreases early in the progression of diabetic retinopathy; however, the mediators and mechanisms responsible for this decrease have yet to be determined. In this study, diabetes was induced by streptozotocin in rats, and retinal blood flow was measured via intravital microscopy 1 or 3 weeks following the induction of hyperglycemia. Additionally, retinal arteriolar diameters and flow were measured prior to and following acute administration of the thromboxane synthase inhibitor ozagrel to investigate the potential role of thromboxane in the observed constriction. Minimal changes in the retinal diameters and flow were observed at 1 week of diabetes; however, at 3 weeks of diabetes, arteriolar constriction and decreases in blood flow were significant. Notably, the constriction occurred only in the arterioles that were in closer proximity to the venules draining the retina. Acute administration of ozagrel reversed the constriction of the closely venule-paired arterioles. In summary, the results suggest that thromboxane mediates localized, venule-dependent arteriolar constriction induced by streptozotocin-induced diabetes in rats.