Summary Arterial hypertension has been identified as a major secondary risk factor for diabetic retinopathy. However, the mechanisms by which hypertension worsens retinopathy are unknown. Inhibition of advanced glycation product formation prevents the development of experimental diabetic retinopathy in normotensive diabetic rats. In this study the effect of hypertension on the rate of diabetic retinopathy development and the formation of arteriolar thrombosis was evaluated. We also evaluated the effect of aminoguanidine, an inhibitor of advanced glycation end product formation on retinal pathology of diabetic hypertensive rats. After 26 weeks of diabetes, hypertension accelerated the development of retinopathy despite a lower mean blood glucose level than in the non-hypertensive group (diabetic spontaneous hypertensive rats (SHR) 16.00 + 6.83 mmol/l; diabetic normotensive Wistar Kyoto rats (WKY) 34.9 + 3.64 mmol/1; p < 0.0001). Diabetic SHR had nearly twice as many acellular capillaries as diabetic WKY (SHR diabetic: 91.9 + 7.5 acellular capillaries per mm 2 of retinal area vs WKY diabetic: 53.7 + 8.5 acellular capillaries per mm 2 of retinal area), and a 3.8-fold increase in the number of arteriolar microthromboses (SHR diabetic 23504 + 5523 gm 2 vs SHR non-diabetic 6228 + 2707 gm2). Aminoguanidine treatment of SHR diabetic rats reduced the number of acellular capillaries by 50 %, and completely prevented both arteriolar deposition of PASpositive material and abnormal microthrombus formation. These data suggest that hypertension-induced deposition of glycated proteins in the retinal vasculature plays a central role in the acceleration of diabetic retinopathy by hypertension. [Diabetologia (1994) 37: 32-35] Key words Diabetic retinopathy, rat model, hypertension, SHR, aminoguanidine, glycation.Over the past few years, hypertension has been identified as a major secondary risk factor for diabetic microvascular complications [1][2][3]. Hypertension accelerates the progression of diabetic nephropathy, and antihypertensive treatment has been shown to reduce declining renal function even in normotensive diabetic subjects [4].Systolic hypertension is also a risk factor for diabetic retinopathy [5][6][7] and in patients with unilateral carotid The mechanisms by which hypertension worsens diabetic retinopathy are unknown. In non-hypertensive diabetic animals, inhibition of advanced glycation product formation (AGE) by aminoguanidine prevents the development of experimental diabetic retinopathy [9]. Since AGEs induce a procoagulatory state in endothelial cells in vitro [10], we hypothesized that increased deposition of glycated plasma proteins in the microvasculature of hypertensive diabetic animals would accelerate diabetic retinopathy by inducing microvascular thrombus formation.In order to test this hypothesis, we examined the effect of aminoguanidine treatment on the retinal pathology of diabetic spontaneously hypertensive rats.

SummaryWe have previously shown that long-term administration of aminoguanidine, an inhibitor of advanced glycosylation product formation, reduces the extent of experimental diabetic retinopathy in the rat by 85 %. In order to determine whether the residual retinopathy that developed despite aminoguanidine was attributable to advanced glycation endproduct formation, a time-course study was performed in three different groups of male Wistar rats: non-diabetic controls (NC), streptozotocin-diabetic controls (DC) and streptozotocin-diabetic rats treated with aminoguanidine HCL, 50 rag/100 ml drinking water (D-AG). Eyes were obtained at 24, 32, 44 and 56 weeks of diabetes/treatment duration and morphologic evaluation was done on retinal digest preparations. At 56 weeks, retinal basement membrane thickness was additionally measured. After 24 weeks of diabetes, the number of acellular capillaries was significantly elevated in DC (44.6 + 5.7/mm 2 of retinal area, NC 19.6 + 4.9; p < 0.001) and increased continuously over time (DC 56weeks 87.4+ 15.1; p < 0.001 vs DC 24 weeks). In contrast, acellular capillaries in D-AG increased over the first 24 weeks and then remained constant for the rest of the study (D-AG 24 weeks 35.7 + 5.18; p < 0.01 vs NC 24 weeks and NS vs DC 24 weeks; D-AG 56 weeks 42.0 + 6.20; p NS vs D-AG 24 weeks). Diabetes-associated pericyte loss (DC 24 weeks 2310 + 170/mm 2 of capillary area; NC 24 weeks 3120+190; p<0.001; DC 56 weeks 1570+230; NC 56 weeks 2960+50; p <0.001) was significantly prevented by aminoguanidine after diabetic-like changes over the initial 24 weeks (D-AG 24 weeks 2450 + 75; p NS vs DC 24 weeks; D-AG 56 weeks 2350 + 90; p < 0.001 vs DC 56 weeks). At 56 weeks, aminoguanidine treatment was associated with a 67.4 % reduction in retinal basement membrane thickening. This time-course study demonstrates that aminoguanidine prevents the progression of experimental diabetic retinopathy, and suggests that non AG-inhibitable mechanisms are involved in the initial phase of diabetic retinopathy. [Diabetologia (1995) 38: 269-273]