Ozagrel attenuates early streptozotocin-induced constriction of arterioles in the mouse retina
Introduction
Diabetic retinopathy (DR) affects hundreds of thousands of Americans over the age of 18 with Type 1 diabetes mellitus (Roy et al., 2004). Human DR often proceeds to proliferative diabetic retinopathy in which new blood vessel growth occurs on the surface of the retina (Fong et al., 2003, Yam and Kwok, 2007), which can interfere with vision. Few symptoms appear prior to the proliferative phase (Yam and Kwok, 2007); however, early treatment is critical to slowing the progression of DR (DCCT Group, 1995, Yam and Kwok, 2007). In early stages of DR, retinal blood flow is reduced substantially (Clermont et al., 1997), and areas of ischemia develop. The contribution of reduced blood flow and ischemia to the eventual disease progression needs further investigation, with the possibility that ischemia could lead to the production of potentially pathological mediators such as vascular endothelial growth factor. As the disease progresses, retinal blood flow increases toward control levels and even exceeds controls when the severity of retinopathy extends beyond microaneurysms only (Clermont et al., 1997).
Animal models of diabetes are used to study the early retinal consequences of hyperglycemia. Diabetic retinopathy is known as a microvascular pathology, and therefore several investigations in diabetic animals have focused on events such as microvascular accumulation of leukocytes and platelets, capillary dropout, altered retinal perfusion, and hypoxia (de Gooyer et al., 2006, De La Cruz et al., 1998, De La Cruz et al., 2000, Joussen et al., 2001, Linsenmeier et al., 1998, Moreno et al., 1995, Yamashiro et al., 2003). However, the mechanisms of early reductions in blood flow in animal models have not established the molecular mediators involved. One such potential mediator is the potent vasoconstrictor thromboxane, which has been implicated in the reduced capillary density found in the streptozotocin-induced rat model of Type I diabetes (De La Cruz et al., 1998, De La Cruz et al., 2000, De La Cruz et al., 2002, Moreno et al., 1995).
Thromboxane-induced vasoconstriction has been investigated in other animal models of inflammation, including ischemia–reperfusion (Mazolewski et al., 1999) and dextran sodium sulfate-induced intestinal inflammation (Harris et al., 2005). In these two models, the vasoactive influence of the constrictor appears to be dependent on the physical arrangement of arterioles and venules in the microvascular bed: thromboxane-induced vasoconstriction of arterioles depends on the proximity of the arteriole to the inflamed venules in which platelets and leukocytes accumulate.
In most microvascular beds of the body, arterioles and venules are found in a close, countercurrent pairing, which can be utilized in feedback regulation of blood flow. This regulation can take the form of venule-induced dilation, for example, in the functional hyperemia that delivers more blood flow upon demand (Hester and Hammer, 2002). In contrast, venule-dependent arteriolar constriction has been reported to occur with inflammatory conditions such as ischemia–reperfusion and hypercholesterolemia (Harris, 1999, Kim et al., 2007, Zamboni et al., 1993). In the retina, alternating arterioles and venules extend from (and into, respectively) the optic disk, and, therefore, it could be expected that venule-dependent modulation of arteriolar flow could be enhanced in the arterioles that are more closely paired with the draining venules.
Therefore, the aims of the present study were to: (1) investigate the extent of arteriolar constriction and retinal blood flow at early time points following induction of hyperglycemia (4 and 8 weeks); (2) determine whether the constriction of arterioles is mediated by thromboxane; and if so, (3) determine whether the thromboxane-dependent arteriolar constriction is more severe in arterioles that are more closely paired with draining venules.
Section snippets
Animals
Animals were treated in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. C57BL/6 mice (Jackson Laboratories), 12 weeks old, were randomly chosen for intraperitoneal (i.p.) injection of streptozotocin (STZ; Sigma, St. Louis, MO; 200 mg/kg dissolved in pH 4.5 sodium citrate buffer) or sodium citrate buffer alone. Animals were injected within 15 min of mixing STZ into solution. Separate experimental groups were used for measurements of red blood cell
Animal data
On the day of STZ injection, there was no difference in body weight between the four groups of mice (Table 1). After 4 weeks and 8 weeks of hyperglycemia, body weight was statistically lower in STZ-injected animals compared with age-matched control animals on the day of experimental measurements. Streptozotocin induced an approximate 2–3 fold increase in non-fasting plasma glucose levels. The measurement range of the glucometer was limited to ≤600 mg/dl, and therefore we report median values (
Discussion
Retinal blood flow in human diabetics follows a biphasic time course of a substantial reduction followed by a later restoration and even increase (Bursell et al., 1996, Clermont et al., 1997). The mechanisms of the initial decrease in flow need to be elucidated, inasmuch as the resulting ischemia could lead to the production of inflammatory and angiogenic mediators such as vascular endothelial growth factor (de Gooyer et al., 2006). The present study demonstrates a biphasic time course of
Acknowledgments
This study was funded by the Juvenile Diabetes Research Foundation (1-2003-159) and by the National Institutes of Health (EY017599).
References (42)
- et al.
Vascular endothelial growth factor and severity of nonproliferative diabetic retinopathy mediate retinal hemodynamics in vivo: a potential role for vascular endothelial growth factor in the progression of nonproliferative diabetic retinopathy
Am. J. Ophthalmol.
(1997) - et al.
Microscopic visualization of the retina by angiography with high-molecular-weight fluorescein-labeled dextrans in the mouse
Microvasc. Res.
(1993) - et al.
Effect of camonagrel, a selective thromboxane synthase inhibitor, on retinal vascularization in experimental diabetes
Eur. J. Pharmacol.
(1998) - et al.
Effect of DT-TX 30, a combined thromboxane synthase inhibitor and thromboxane receptor antagonist, on retinal vascularity in experimental diabetes mellitus
Thromb. Res.
(2000) - et al.
Leukocyte-mediated endothelial cell injury and death in the diabetic retina
Am. J. Pathol.
(2001) - et al.
Mediators of CD18/P-selectin-dependent constriction of venule-paired arterioles in hypercholesterolemia
Microvasc. Res.
(2007) - et al.
Tonopen measurement of intraocular pressure in mice
Exp. Eye Res.
(2004) - et al.
Evaluation of carbocyanine-labeled erythrocytes for microvascular measurements
Microvasc. Res.
(1993) - et al.
Platelets accumulate in the diabetic retinal vasculature following endothelial death and suppress blood–retinal barrier breakdown
Am. J. Pathol.
(2003) - et al.
Hemodynamic parameters in blood vessels in choroidal melanoma xenografts and rat choroid
Invest. Ophthalmol. Vis. Sci.
(2002)
Estimation of retinal blood flow by measurement of the mean circulation time
Cardiovasc. Res.
Retinal blood flow changes in patients with insulin-dependent diabetes mellitus and no diabetic retinopathy
Invest. Ophthalmol. Vis. Sci.
Evaluating retinal circulation using video fluorescein angiography in control and diabetic rats
Curr. Eye Res.
Normalization of retinal blood flow in diabetic rats with primary intervention using insulin pumps
Invest. Ophthalmol. Vis. Sci.
Retinal blood flow by hydrogen clearance polarography in the streptozotocin-induced diabetic rat
Invest. Ophthalmol. Vis. Sci.
The effect of intensive diabetes treatment on the progression of diabetic retinopathy in insulin-dependent diabetes mellitus
The Diabetes Control and Complications Trial. Arch. Ophthalmol.
Retinopathy is reduced during experimental diabetes in a mouse model of outer retinal degeneration
Invest. Ophthalmol. Vis. Sci.
Effect of aspirin on prostanoids and nitric oxide production in streptozotocin-diabetic rats with ischemic retinopathy
Naunyn Schmiedebergs Arch. Pharmacol.
Macrophages in proliferative vitreoretinopathy and proliferative diabetic retinopathy: differentiation of subpopulations
Br. J. Ophthalmol.
Diabetic retinopathy
Diabetes Care
Regulation of uveal and retinal blood flow in STZ-diabetic and non-diabetic rats: involvement of nitric oxide
Curr. Eye Res.
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