Morphometric studies on retinal microangiopathy and myocardiopathy in hypertensive rats (SHR) with induced diabetes

The renin-angiotensin system influences ocular endothelial cell proliferation in diabetes: transgenic and interventional studies

Neovascularization in the retina and iris of diabetic patients is a major cause of severe visual loss. However, study of these lesions is compromised by the lack of a comparable diabetic rodent model. Because the vasoactive and angiogenic agent, angiotensin II, is involved in diabetic microvascular disease, we aimed to determine whether endothelial cell proliferation could be induced in the retinae and irides of hypertensive transgenic (mRen-2)27 rats that display an enhanced extra-renal renin-angiotensin system (RAS), including the eye. Six-week-old Ren-2, spontaneously hypertensive, and Sprague-Dawley rats received either streptozotocin or control vehicle and were studied for 36 weeks. Additional nondiabetic and diabetic Ren-2 rats were treated throughout with the angiotensin-converting enzyme inhibitor lisinopril (LIS) (10 mg/kg/day in drinking water). Endothelial cell proliferation was only observed in retinae and irides of diabetic Ren-2 rats and was reduced with LIS. In diabetic Ren-2, vascular endothelial growth factor (VEGF) and VEGFR-2 mRNA were increased in retinae and irides and reduced with LIS. Diabetes activated ocular renin in Ren-2 but not Sprague-Dawley rats. The diabetic Ren-2 rat is a model of intraocular endothelial cell proliferation that can be attenuated by RAS blockade via VEGF-dependent pathways. RAS blockade is a potential treatment for vision-threatening diabetic microvascular complications.

Long-term effects of high calorie sucrose-enriched diet and streptozotocin-induced diabetes on insulin resistance in spontaneously hypertensive rats

1. The effects of two experimental manipulations on insulin resistance were compared in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Rats were fed a high calorie sucrose-enriched diet (high calorie diet) or were made diabetic by the injection of streptozotocin (STZ). 2. After treatment with the high calorie diet for 8 weeks, blood pressure increased in SHR, but not in WKY rats. In contrast, STZ treatment decreased blood pressure in SHR, but increased it in WKY rats. 3. Plasma glucose levels during oral glucose loading were higher in SHR than in WKY rats. Glucose tolerance was impaired to a greater extent by both the high calorie diet and STZ in SHR than in WKY rats. Hyperinsulinaemia induced by the high calorie diet was severe in SHR compared with WKY rats. 4. Abnormalities in lipid metabolism induced by a high calorie diet or STZ-induced diabetes were more marked in SHR than in WKY rats. 5. Steady-state plasma glucose levels in the insulin suppression test were higher in SHR than in WKY rats, both of which were treated by either the high calorie diet or STZ. These findings indicate that insulin-stimulated glucose uptake by high calorie diet or STZ-induced diabetes was impaired to a greater extent in SHR than in WKY rats. 6. It is concluded, therefore, that SHR fed on high calorie diet or SHR with STZ-induced diabetes are suitable models to study the effects of antihypertensive treatment on glucose tolerance, insulin resistance or lipid metabolism as well as blood pressure.

Effect of antihypertensive treatment with alacepril on insulin resistance in diabetic spontaneously hypertensive rats

Recent clinical reports have described the close relationship between insulin resistance and hypertension. Previous reports from our laboratory documented that spontaneously hypertensive rats (SHR) have mild insulin resistance, and that this insulin resistance is more intense in SHR with diabetes induced by streptozotocin (STZ). The aim of this study was to elucidate the effects of antihypertensive treatment with alacepril on insulin resistance in these diabetic SHR. Animals were divided into four groups as follows: group A, nondiabetic SHR; group B, diabetic SHR group C, diabetic SHR treated with 0.05% alacepril; and group, D diabetic SHR treated with 0.1% alacepril. Diabetes was induced by intravenous (IV) injection of STZ (35 mg/kg bodyweight [BW]). Alacepril was given orally by mixing in laboratory chow. Mean (+/- SD) blood pressure was lowered in the alacepril-treated groups (A 212 +/- 7mm Hg and B 213 +/- 8 v C 184 +/- 6 and D 167 +/- 9; P < .01). Total integrated plasma glucose levels were different among all the groups by oral glucose tolerance test (OGTT) (B 53.6 +/- 3.3 mmol/L > C47.2 +/- 4.5 > D 42.3 +/- 1.4 > A 34.2 +/- 1.2; P < .01). Steady-state plasma glucose (SSPG during the insulin suppression test was higher in group B than in group A (15.7 +/- 1.5 mmol/L v 10.4 +/- 0.8; P < .001). The SSPG level (12.9 +/- 0.7) was significantly (P < .001) lower in group D than in untreated group B. In the diabetic groups, blood pressure was positively correlated with integrated plasma glucose (PG) (r = .79, P < .001), SSPG (r = .53, P < .02), and plasma triglyceride (r = .70, P < .001), and negatively with high-density lipoprotein (HDL)-cholesterol (r = -.74, P < .001). Alacepril treatment not only dose-relatedly lowered mean blood pressure, but also dose-relatedly improved abnormalities in carbohydrate and lipid metabolism in STZ-induced diabetic SHR. These results suggest that an angiotensin-converting enzyme inhibitor, alacepril, has an antihypertensive effect, but also improves insulin resistance in hypertension with diabetes mellitus.

Decreased skin blood flow early in the course of streptozotocin-induced diabetes mellitus in the rat

We have previously used laser Doppler technology to demonstrate that skin blood flow is reduced in Type 1 (insulin-dependent) diabetic patients. The possibility of using the skin as an extremely accessible indicator of diabetic microvascular disease is attractive. The streptozotocin diabetic rat is an appealing potential animal model. We performed measurements of skin blood flow in two rat species, nine Sprague Dawley (SD) rats and nine Wistar Kyoto (WKY) rats, observing early changes following the inception of diabetes. Four of the SD rats and five of the WKY rats were made diabetic, the rest serving as controls. There were no significant differences in skin blood flow between the two rat strains. As in man, there appear to be rat skin sites with primarily nutritive capillary supply and those with arteriovenous anastomotic predominance. The back and base of tail, both hair-covered areas, demonstrated low flow characteristics, consistent with nutritive perfusion. In contrast, the plantar surface of the paw behaved similarly to the finger or toe pulps in man, sites of arteriovenous perfusion, with high basal flow and a marked increment with thermal stimulation. In diabetic rats of both species, there was significantly lower flow at the back and base of tail than in non-diabetic animals. The differences were of the order of 30-40%. As a function of time, the decrease in blood flow at the base of tail parallelled the increase in glycohaemoglobin levels in the diabetic rats. In contrast, blood flow at the plantar surface of the paw was unchanged throughout the 3-month post-streptozotocin observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertensive diabetic rats: different effects of streptozotocin treatment on blood pressure in adult SHR and in neonatal SHR

The effect of streptozotocin (STZ) treatment on blood pressure in adult spontaneously hypertensive rats (SHR) was compared with that in neonatal SHR. Three-month-old SHR were intravenously given 10, 30 or 50 mg/kg of STZ. When STZ was given in adult SHR, weight loss, overt hyperglycemia and the reduction of blood pressure occurred dose dependently. Two-day-old pups from SHR were subcutaneously injected with 100 mg/kg of STZ. Neonatal STZ treatment did not attenuate the development of hypertension in SHR. Since neonatally STZ-treated SHR develop mild diabetic symptom with hypertension and develop mild diabetic glomerulosclerosis, they are a good model for studying vascular complications or other disorder relating to the synergism between hypertension and diabetes mellitus.

A non-mammalian in vivo model for cellular and molecular analysis of glucose-mediated thickening of basement membranes

An increase of basement membrane thickness in renal glomeruli, blood vessels, and other tissues is a consistent pathological observation in individuals with diabetes mellitus. Although a number of pathological complications of the disease are thought to result from this structural abnormality in basement membranes, the mechanism(s) responsible for this glucose-mediated process remain unknown. The current study was designed to develop a non-mammalian in vivo epithelial/basement membrane model which would facilitate detailed analysis of the cellular and molecular processes which lead to thickening of basement membrane under hyperglycaemic conditions. The system developed utilizes the Cnidarian, Hydra vulgaris. Hydra lends itself to such studies because of (1) its simplified body structure which is composed of an epithelial bilayer with an intervening basement membrane (mesoglea) and (2) its extensive regenerative capacity which allows cell pellets (Hydra cell aggregates), formed from isolated Hydra cells, to develop into adult Hydra within 72-96 h. This process involves reformation of an epithelial bilayer and de novo biosynthesis of a basement membrane. Our studies indicate that exposure of developing Hydra cell aggregates to levels of D-glucose which mimic that observed in the human diabetic patient (15 mmol/l) induces a doubling of Hydra basement membrane thickness within 72-96 h of pellet formation. The same results were obtained using 15 mmol/l D-Ribose which is a highly efficient glycating agent. The data presented support the use of the Hydra cell aggregate system as a potentially powerful non-mammalian in vivo model to investigate the cellular and molecular mechanism(s) underlying glucose-mediated basement membrane thickening.

New establishment of hypertensive diabetic animal models: neonatally streptozotocin-treated spontaneously hypertensive rats

Hypertensive diabetic animal models have been developed by injecting streptozotocin (STZ) in neonatal stroke-resistant spontaneously hypertensive rats (SHRSR) and stroke-prone SHR (SHRSP) at the age of two days. After the treatment, the animals showed mild insulin deficiency and mild hyperglycemia at the age of three to four months. Diabetic nephropathy was produced particularly in STZ-treated SHRSR at the age of six months. The effect of neonatal STZ injection on hyperglycemia varied among normotensive Wistar-Kyoto rats (WKY), SHRSR, and SHRSP; SHRSR showed the highest glucose levels, SHRSP showed intermediate levels, and WKY was the lowest. All STZ-treated SHRSR showed glycosuria, while glycosuria was not observed in the treated SHRSP and WKY. Histologic study indicated that these strain differences were partly ascribed to differences in islet B-cell sensitivity to toxic effects of STZ. The development of hypertension was not accelerated in these SHRSR and SHRSP compared with respective nontreated controls. Since STZ-treated SHRSR develop mild diabetic symptom with hypertension and develop mild diabetic glomerulosclerosis, they are good models for studying vascular complications or other problems relating to the synergism between hypertension and diabetes mellitus.

Synergistic effects of diabetes mellitus and renovascular hypertension on the rat heart--stereological investigations on papillary muscles

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive nondiabetic young male Wistar rats were compared with diabetic and non-diabetic controls. Since the normal body weight increase of the diabetic animals was markedly suppressed a weight-matched nondiabetic control group was introduced in addition. Hypertension was established for eight weeks by a surgical stenosis of the left renal artery, diabetes mellitus was maintained for four weeks after a single intraperitoneal injection of 75 mg/kg streptozotocin. Light and electron microscopic stereological parameters were obtained for the left ventricular papillary muscles. The whole hearts were also investigated histologically. Qualitative morphology failed to substantiate synergistic effects in the hypertensive diabetic rats. Vascular abnormalities were not observed. The stereological parameters, however, revealed microstructural reactions which were observed exclusively in the hypertensive diabetic group: the volume ratio of mitochondria-to-myofibrils was decreased, the surface-to-volume ratio of mitochondria was increased (reduction of mitochondrial size) and the mean cross sectional area of capillaries was decreased. Similar quantitative mitochondrial changes have been frequently described in long-standing hypertension, but in the present investigation, they were not found in the nondiabetic hypertensive group. It is therefore concluded that diabetes mellitus potentiates the effects of chronic pressure overload on myocardial cells. However, the myocardial fibrosis which has been found by other groups at later stages of hypertension and/or diabetes mellitus was not detected in the present study. The reduced mean cross sectional area of capillaries in hypertensive-diabetic rats may be correlated with early molecular changes of the myocardial interstitium or with early abnormalities of small arteries. Thus our stereological results support the hypothesis that a non-coronary hypertensive diabetic cardiomyopathy occurs in mammalian hearts.

Accelerated progression of diabetic nephropathy in the spontaneously hypertensive streptozotocin diabetic rat

Streptozotocin (STZ)-diabetes was induced in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats with their litter mates serving as controls. The animals were studied for 6 months and blood pressure, weight, urinary and serum glucose, creatinine clearance, total proteinuria and albuminuria were measured monthly. With induction of diabetes, there was a significant rise in creatinine clearance in the hypertensive diabetic animals (SHR-STZ). SHR-STZ (n = 6) developed higher levels of total proteinuria than WKY-STZ (n = 5) although the rise from basal levels was only apparent after 20 weeks of diabetes. All SHR-STZ developed albustix positive proteinuria after 6 months of diabetes. In the first 12 weeks after onset of diabetes, albuminuria increased to a greater degree in SHR-STZ than in WKY-STZ. This occurred before there was a detectable rise in total proteinuria. The SHR-STZ model of genetic hypertension and diabetes may be suitable for the evaluation of antihypertensive therapy in human diabetic renal disease.

Hypothalamic and cortical neurons of normotensive and spontaneously hypertensive rats are differently affected by streptozotocin diabetes

Diabetic encephalopathy is a relatively frequent late complication in human and experimental diabetes mellitus. Although it is generally assumed that microangiopathy plays a major role in its pathogenesis, many aspects of the latter are still poorly understood. To detect possible correlations between vascular and cellular changes, we examined in normotensive and spontaneously hypertensive streptozotocin diabetic rats the neurons of hypothalamic and cortical regions in which the capillary basement membrane thickness had been known from a previous study. Arcuate and ventromedial nucleus neurons of normotensive diabetic rats compared to those of corresponding controls showed a reduced cytoplasmic area after 4 but not after 8 months of experiment. No difference was found between hypertensive control and diabetic rats after either 4 or 8 months of experiment. After the 8th month cortical neurons of normotensive controls were smaller in an occipital than in a frontal region and within the same region in the following layer order: deep less than superficial less than intermediate. Neurons of hypertensive controls behaved comparably yet were generally smaller than those of normotensive controls in each corresponding region. Compared to those of control, cortical neurons of normotensive diabetic rats were smaller in superficial and deep layers of both regions and in the intermediate layer of the frontal region. Hypertension appeared to antagonize diabetes. Despite an arcuate nucleus microangiopathy found in rats from both strains after 4 and 8 months of diabetes, neuronal changes were seen only in normotensive animals after 4 months. In the intermediate cortical layer, where microangiopathy was most marked after 8 months of experiment, neurons were not or only slightly reduced in size.(ABSTRACT TRUNCATED AT 250 WORDS)

Basement membrane of hypothalamus and cortex capillaries from normotensive and spontaneously hypertensive rats with streptozotocin-induced diabetes

Basement membrane (BM) thickness of hypothalamic arcuate nucleus capillaries was measured in normotensive (WKY) and hypertensive (SHR) rats 4 and 8 months after streptozotocin or saline injection. Three groups were studied: controls (C), diabetics (D), and animals with impaired glucose tolerance (L). For comparison, BM thickness of cortical capillaries of an occipital and a frontal area was measured in three different layers starting from the pial surface. Independently from strain, hypothalamic capillary BM was thicker in older than in younger animals. At both 4 and 8 months, BM thickness was lowest in C, highest in D, and intermediate (between C and D) in L. Hypertension combined with diabetes did not further increase BM thickness. In both C and D no difference was found between the two cortical areas. The BM thickness of C increased from the superficial to the deep layer. In C hypertension induced BM thickening in the superficial frontal and the deep occipital layer. In the intermediate and the deep layer of the frontal area BM was thicker in WKY-D than in WKY-C. In every layer BM was thicker in SHR-D than in corresponding controls. Hypertension combined with diabetes enhanced BM thickening in the intermediate and the deep layer of the frontal and in the intermediate layer of the occipital area. Degenerative changes occurred in hypothalamic and cortical pericytes. These changes were more frequent in hypertensive than in normotensive animals. In conclusion, a microangiopathy characterized by BM thickening and pericytic degeneration occurs in the brain of diabetic animals. Its intensity and enhancement by a concomitant hypertension vary from hypothalamus to cortex.