Male Otsuka Long-Evans Tokushima Research Articles

The induction of insulinomas by X-irradiation to the gastric region in Otsuka Long-Evans Tokushima Fatty rats

The X-ray induction of tumors was examined in five-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, treated with two 10 Gy doses to the gastric region with a 3-day interval (total 20 Gy). After irradiation, the rats received the commercial diet MF and tap water and were maintained for up to 564 days. The mean serum glucose level in the X-irradiated group was significantly lower than that in the non-irradiated animals at the 18 month time point. The total tumor incidence was 27/30 (87.1%) in the treated rats (islet tumors, gastric tumors, sarcomas, seminomas, adrenal tumors, kidney tumors, papilloma, lymphomas and mammary tumors). Islet tumors, generally showed to be positive for insulin by immunohistochemistry, developed in 19 rats (63.3%), and were associated with low serum glucose. Since spontaneous tumors observed in 6/19 (31.6%) rats (sarcomas, kidney tumors, duodenum tumors, seminoma, adrenal tumor and squamous cell carcinoma) did not include any insulinomas, these are clearly induced by X-irradiation in OLETF rats.

Protein kinase C δ regulates anti-apoptotic αB-crystallin in the retina of type 2 diabetes

We investigated the relationship between phosphorylation of alphaB-crystallin (alphaBC) and retinal apoptosis in type 2 diabetes. The retinas of male Otsuka Long-Evans Tokushima fatty (OLETF) rats at 24 and 35 weeks were used as an animal model for type 2 diabetes and sex- and age-matched Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In the retinas of 35-week OLETF rats, the interaction between alphaBC and protein kinase C delta (PKC delta) among the PKC isozymes, alphaBC phosphorylation at Ser45 (S45p-alphaBC), TUNEL-positive apoptotic ganglion cells, several apoptotic signs, and co-localization of S45p-alphaBC and TUNEL significantly increased as compared with other groups while the alphaBC-Bax interaction greatly decreased. These changes were abolished by rottlerin treatment, a highly specific PKC delta inhibitor. These results suggest that PKC delta is involved in regulation of anti-apoptotic function of alphaBC in the retina of type 2 diabetes.

β1 antagonist and β2 agonist, celiprolol, restores the impaired endothelial dependent and independent responses and decreased TNFα in rat with type II diabetes

The effect of β antagonists in the diabetic vascular lesion is controversial. We investigated the effect of celiprolol hydrochloride, a β1 antagonist and mild β2 agonist, on the lesions and function in type II male Otsuka Long-Evans Tokushima Fatty (OLETF) diabetic rats. OLETF rats were fed regular chow with or without atenolol (25 mg/kg/day) or celiprolol (100 mg/kg/day) treatment (group DM, no treatment; group DM-a, atenolol treatment; group DM-c, celiprolol treatment), and treatment was continued for 31 days. Separately, normoglycemic control rats, LETO, were prepared as group C. On day 3, endothelial cells of the right internal carotid artery were removed by balloon injury, and the rats were evaluated 4 weeks after balloon injury. The plasma glucose and lipid levels were unchanged throughout the treatment period. Intimal thickening was observed in the right carotid artery in the DM and DM-a groups; however, little thickening was observed in those of DM-c rats. Acetylcholine-induced NO-dependent relaxation in arteries was improved in DM-c rats compared with DM and DM-a rats (maximum relaxation DM 30.8 ± 4.5, DM-a 37.4 ± 3.9, DM-c 48.8 ± 4.6%, ⁎ P < 0.05 vs. DM for DM-c rats). Tone-related basal NO release and acetylcholine-induced NO-dependent relaxation in the arteries and plasma NO x (sum of NO 2 − and NO 3 −) were greater in DM-c and C groups than in DM and DM-a groups. The serum TNFα levels did not increase in DM-c rats compared with those of the DM or DM-a groups, and were comparable with those of group C. Conclusion In conclusion, Celiprolol improves endothelial function in the arteries of OLETF rats, and further restore it 4 weeks after endothelial denudation in the arteries of OLETF rats. NO and O 2 − may have a role in the important underlying mechanisms by reducing the TNFα levels.

Pioglitazone but Not Glibenclamide Improves Cardiac Expression of Heat Shock Protein 72 and Tolerance Against Ischemia/Reperfusion Injury in the Heredity Insulin-Resistant Rat

We tested the hypothesis that pioglitazone could restore expression of heat shock protein (HSP)72 in insulin-resistant rat heart. At 12 weeks of age, male Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control (LETO) rats were treated with pioglitazone (10 mg x kg(-1) x day(-1)) or glibenclamide (5 mg x kg(-1) x day(-1)) for 4 weeks. Thereafter, hyperthermia (43 degrees C for 20 min) was applied. In response to hyperthermia, the activation of serine/threonine kinase Akt depending on phosphatidylinositol 3 (PI3) kinase was necessary for cardiac expression of HSP72. Hyperthermia-induced activation of Akt and HSP72 expression were depressed in OLETF rat hearts. Pioglitazone but not glibenclamide improved insulin sensitivity in OLETF rats, which was associated with the restoration of Akt activation and HSP72 expression. In experiments with isolated perfused heart, reperfusion-induced cardiac functional recovery was suppressed in OLETF rat hearts, which was improved by pioglitazone but not glibenclamide. Our results suggest that PI3 kinase-dependent Akt activation, an essential signal for HSP72 expression, is depressed in the heart in insulin-resistant OLETF rats, and the results suggest also that the restoration of HSP72 expression and tolerance against ischemia/reperfusion injury by treatment with pioglitazone might be due to an improvement of insulin resistance, leading to restoration of impaired PI3 kinase-dependent Akt activation in response to hyperthermia.

Thiazolidinediones Ameliorate Diabetic Nephropathy via Cell Cycle–Dependent Mechanisms

Thiazolidinediones are ligands for peroxisome proliferator-activated receptor (PPAR)-gamma, widely used as insulin sensitizer in type 2 diabetic patients and implicated in apoptosis, cell proliferation, and cell cycle regulation. Here, the effect of thiazolidinediones on G1-phase cell cycle arrest, the hallmark in diabetic nephropathy, was investigated. Eight-week-old male Otsuka Long-Evans Tokushima fatty rats were treated with pioglitazone (1 mg x kg body wt(-1) x day(-1)) until 50 weeks of age and compared with insulin treatment. Although similar HbA(1c) levels were observed in both groups, pioglitazone significantly inhibited glomerular hypertrophy and mesangial matrix expansion and reduced urinary albumin excretion compared with the insulin-treated group. In addition, pioglitazone significantly reduced the number of glomerular p27(Kip1)-positive cells. Because prominent expression of PPAR-gamma was observed in podocytes in glomeruli and cultured cells, conditionally immortalized mouse podocyte cells were cultured under 5.5 and 25 mmol/l D-glucose supplemented with pioglitazone. Pioglitazone inhibited cell hypertrophy revealed by [(3)H]thymidine and [(3)H]proline incorporation, and pioglitazone reversed high glucose-induced G1-phase cell cycle arrest, i.e., an increase in G0/G1 phase and decrease in S and G2 phases. Pioglitazone suppressed high glucose-induced phosphorylation of p44/42 mitogen-activated protein kinase and reduced Bcl-2 and p27(Kip1) protein levels. Besides glucose-lowering action, pioglitazone ameliorates diabetic nephropathy via cell cycle-dependent mechanisms.

Morphological Changes of Pancreatic Ducts in Otsuka Long-Evans Tokushima Fatty Rats

To determine if pancreatic ductal changes characteristic of chronic pancreatitis occur in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats and to elucidate the 3-dimensional structure of the pancreatic ducts in those rats. Male OLETF rats aged 10, 20, and 40 weeks were used. The pancreas was injected with a 120% barium sulfate suspension into the pancreatic ducts, after which radiograph images of the injected pancreas were taken using radiography of the soft parts. Conventional fixed pancreatic tissues were observed by the use of light and scanning electron microscopy, whereas corrosion casts of the pancreatic ducts were observed by the use of scanning electron microscopy. In 20- and 40-week-old male OLETF rats, deletion of acini and formation of tubular complexes and tortuous or helical, deformed, dilated pancreatic ducts were found, whereas the inner surfaces of pancreatic ducts had many craterlike depressions and long cilia. Male OLETF rats demonstrated the same morphological changes in pancreatic ductal lumina and histological changes in pancreatic tissues as the rats were subjected to pancreatic duct ligation. These results suggested that increased pancreatic duct pressure occurs in male OLETF rats and induces the chronic pancreatitis-like lesions, including the above-mentioned findings.

Azelnidipine Down-Regulates Renal Angiotensin-Converting Enzyme and Mineralocorticoid Receptor mRNA in Diabetic Hypertensive Rats

Effects of a new lipophilic L-type calcium channel blocker, azelnidipine, on the expression of molecular components of the renin-angiotensin-aldosterone system (RAAS) were assessed. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of diabetes with hypertension, and their lean littermates, Long-Evans Tokushima Otsuka (LETO) rats, were treated with azelnidipine for 2 weeks. The renal cortical mineralocorticoid receptor mRNA in OLETF was higher than in LETO, but was suppressed (P<0.05) by azelnidipine. Renal cortical angiotensin-converting enzyme mRNA of OLETF was lower than that of LETO rats, and it was further suppressed by azelnidipine (P<0.05). Azelnidipine can down-regulate the gene expression of molecular components of RAAS.

Effects of running exercise on fibre‐type distribution of soleus and plantaris muscles in diabetic Otsuka Long‐Evans Tokushima fatty rats

Effect of running exercise on fibre-type distributions of the slow soleus and fast plantaris muscles was investigated in male Otsuka Long-Evans Tokushima fatty rats (OLETF) as an animal model of spontaneous type 2 diabetes mellitus. Five-week-old OLETF rats were allowed to exercise voluntarily in running wheels for 32 days and the data were compared with those of age-matched non-exercised OLETF and non-diabetic Long-Evans Tokushima Otsuka rats (LETO). In the soleus muscle, a higher percentage of type I fibres was observed in non-exercised OLETF rats compared with LETO rats, and there were no type IIA fibres in non-exercised OLETF rats. In the plantaris muscle, a higher percentage of type IIB fibres and a lower percentage of type I and type IIA fibres were observed in non-exercised OLETF rats compared with LETO rats. In contrast, there were no differences in the fibre-type distribution of soleus and plantaris muscles between exercised OLETF and LETO rats. The body weight and type I fibre percentage of the soleus muscle were related to the running distance in exercised OLETF rats. White adipose tissue weight, HbA(1c) and blood insulin and glucose concentrations were lower in exercised OLETF rats than in non-exercised OLETF rats, irrespective of the running distance. There was a difference in the gene-expression pattern of the soleus muscle among LETO rats, non-exercised OLETF and exercised OLETF rats. Running exercise can inhibit diabetes-associated type shifting of fibres, which is more apparent with postnatal growth, in skeletal muscles of diabetic OLETF rats, as a result of mRNA expression change in muscle.

The Calcium Channel Antagonist Benidipine Reduces Plasma and Cardiac Endothelin-1 Levels in Type II Diabetic Rat Model

Cardiovascular complications are the central feature of type 2 diabetes mellitus, and insulin resistance is an early clinical manifestation of type 2 diabetes mellitus. Calcium channel blockers are widely used to treat cardiovascular diseases in diabetic patients; however, it remains unknown how endothelin-1 (ET-1) is altered and associated with cardiac lesions at the insulin-resistant early stage of type 2 diabetes mellitus, and, if so, whether calcium channel blockers can reverse such alterations. We examined plasma and cardiac expression of ET-1 in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a spontaneous model of human type 2 diabetes mellitus. At 8 weeks of age, OLETF rats were treated for 12 weeks with a long acting calcium channel blocker, benidipine (3 mg/kg per day p.o.) (BEN, n = 15), or with vehicle (OLETF, n = 15), and age-matched genetic control, male Long-Evans Tokushima Otsuka (LETO) rats were also used (n = 15). Blood pressure was significantly higher in OLETF than LETO rats, and benidipine treatment of OLETF rats for 12 weeks did not reduce their blood pressure significantly. Plasma and cardiac levels of ET-1 were significantly higher in OLETF compared with LETO rats (both P < 0.01), and were reversed after benidipine treatment. Our results suggest that ET-1 plays a pivotal role in the pathogenesis of cardiac complications at the insulin-resistant stage of diabetes mellitus, and that benidipine treatment may have a beneficial effect on these complications.

Nitrogen dioxide air pollution near ambient levels is an atherogenic risk primarily in obese subjects: a brief communication.

Ambient exposure to nitrogen dioxide, a critical air pollutant in developed countries, is positively associated with cardiovascular mortality and morbidity. Although its cardiovascular effects are predominantly shown in patients with high risk of atherogenesis, no studies have elucidated whether daily exposure to nitrogen dioxide air pollution enhances atherogenic metabolisms, primarily in obese subjects who are susceptible to atherogenesis and subsequent cardiovascular diseases. We used male Otsuka Long-Evans Tokushima Fatty (OLETF) rats as obese subjects and Long-Evans Tokushima (LETO) rats as nonobese controls. The animals were continuously exposed to nitrogen dioxide at a concentration of 0, 0.16, 0.8, or 4.0 ppm from 8 weeks of age through 32 weeks. At 40 weeks of age, levels of body weight, triglyceride, and total cholesterol were significantly greater in the OLETF rats than in the LETO rats. A ratio of high-density lipoprotein (HDL) to total cholesterol was significantly smaller in the former than in the latter. In the LETO rats, nitrogen dioxide exposure significantly decreased only the levels of HDL as compared with clean air exposure. In the OLETF rats, however, nitrogen dioxide exposure at a concentration of 0.16 ppm significantly elevated triglyceride concentration and decreased the ratio of HDL to total cholesterol as well as the levels of HDL. Nitrogen dioxide air pollution near ambient levels is an atherogenic risk primarily in obese subjects.

Efficacy of edaravone, a free radical scavenger, on left ventricular function and structure in diabetes mellitus.

This study was designed to assess the efficacy of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger that possesses anti-oxidant effects, on cardiac function and fine structure of the left ventricular myocardium in diabetes mellitus. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of spontaneous development of type II diabetes (30 weeks; n = 15) were divided into two groups and treated with edaravone 30 mg/kg/d or vehicle for 2 weeks. OLETF rats showed hyperglycemia (352 +/- 71 mg/dl vs normal control; 128 +/- 52 mg/dl), increased thiobarbituric acid-reactive substances (TBARS; 6.9 +/- 2.5 nM/ml vs 2.8 +/- 0.6 nM/ml), and decreased superoxide dismutase activity (21.5 +/- 0.9 U/ml vs 25.8 +/- 0.7 U/ml). Increased left ventricular end-diastolic pressure (12 +/- 3 mm Hg vs 6 +/- 2 mm Hg) and hypertrophied cardiocytes (23.1 +/- 1.4 vs 17.6 +/- 1.0 microm) were also observed (P < 0.05, respectively). Edaravone could not improve plasma glucose level and hemodynamic parameters but significantly decreased TBARS values (3.8 +/- 0.5) and increased superoxide dismutase activity (24.5 +/- 0.8) (vs OLETF, P < 0.05, respectively). Moreover, edaravone effectively preserved cardiocyte diameter (18.2 +/- 0.9 microm) and the fine structure of mitochondria. Thus, edaravone exhibits modest cardiac protection in diabetes mellitus independent of blood sugar level.

Effects of troglitazone on skeletal muscle and liver protein tyrosine phosphatase activity in insulin-resistant otsuka long-evans tokushima fatty rats

Background: Protein tyrosine phosphatases (PTPases) appear to play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin-signaling pathway. Objectives: This study determined the role of PTPases in skeletal muscle and liver in an insulin-resistant model and the in vivo effect of troglitazone on PTPases. Methods: We used 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats as models of insulin resistance. PTPase activity was assessed with reduced carboxyamido-methylated and -maleylated lysozyme as substrates. The protein levels of 3 major candidate PTPases—leukocyte common antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2)—in skeletal muscle and liver of OLETF rats were analyzed using Western blot. The activities and amounts of PTPases in skeletal muscle and liver of OLETF rats treated with troglitazone for 7 days also were examined. Results: Particulate and cytosolic PTPase activities in skeletal muscle of OLETF rats were increased compared with those in control rats. Similar changes were observed in the liver. The protein levels of LAR, PTP1B, and SH-PTP2 in particulate fractions of skeletal muscle of OLETF rats were increased, but levels of PTP1B and SH-PTP2 in cytosolic fractions were unchanged. Similar findings were observed in the liver. Troglitazone normalized the increased PTPase activity and each protein level except cytosolic fraction of the liver. Conclusions: The findings suggest that troglitazone decreases elevated activities and levels of PTPases in the particulate fraction of the skeletal muscle and liver of OLETF rats, and that PTPase plays important roles through regulating the insulin-signaling system in the pathogenesis of insulin resistance in OLETF rats.

Insulin and glucagon secretions, and morphological change of pancreatic islets in OLETF rats, a model of type 2 diabetes mellitus.

This study was performed to observe the changes of glucose-related hormones and the morphological change including ultrastructure of the pancreatic islets in the male Otsuka Long-Evans Tokushima Fatty rat. Area under the curve (AUC) of glucose at the 30th (709 plus minus 73 mg.h/dL) and at the 40th week (746 plus minus 87 mg.h/ dL) of age were significantly higher than that at the 10th week (360 plus minus 25 mg.h/ dL). AUC of insulin of the 10th week was 2.4 plus minus 0.9 ng.h/mL, increased gradually to 10.8 plus minus 8.3 ng.h/mL at the 30th week, and decreased to 1.8 plus minus 1.2 ng.h/mL at the 40th week. The size of islet was increased at 20th week of age and the distribution of peripheral alpha cells and central beta cells at the 10th and 20th weeks was changed to a mixed pattern at the 40th week. On electron microscopic examination, beta cells at the 20th week showed many immature secretory granules, increased mitochondria, and hypertrophied Golgi complex and endoplasmic reticulum. At the 40th week, beta cell contained scanty intracellular organelles and secretory granules and apoptosis of acinar cell was observed. In conclusion, as diabetes progressed, increased secretion of insulin was accompanied by increases in size of islets and number of beta-cells in male OLETF rats showing obese type 2 diabetes. However, these compensatory changes could not overcome the requirement of insulin according to the continuous hyperglycemia after development of diabetes.

A role of oxidative stress-generated eicosanoid in the progression of arteriosclerosis in type 2 diabetes mellitus model rats.

Diabetes mellitus (DM) is a well-established risk factor of cardiovascular diseases. We investigated the mechanism of the progression of arteriosclerosis in DM, focusing on the role of oxidative stress and insulin resistance in vivo. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an experimental model of type 2 DM, were assigned to 3 groups, based on supplementation with vitamin E (VE) or troglitazone (TR), a VE-derived agent which improves insulin-resistance. At 36 weeks, plasma and aortic tissue 8-iso-PGF2alpha contents, a vascular proliferating eicosanoid produced in vivo by oxidative stress, were measured by EIA. TGF-beta1 and TGF-beta1 receptor II were immunohistochemically analyzed. Histopathologically, medial area and the nuclear number of smooth muscle cells of the aorta were measured. The tissue 8-iso-PGF2alpha content (pg/g tissue) was significantly decreased by either VE or TR in the aorta (untreated-OLETF, 15,332+/-3,254 vs. TR-treated-OLETF, 7,092+/-1,992 or VE-treated-OLETF, 5,394+/-836, both p<0.01), but that in plasma decreased by only VE. VE and TR improved the increased the level of the actual medial area and the number of smooth muscle cells. The expression of TGF-beta1 was reduced, but TGF-beta1 receptor II was not. 8-iso-PGF2alpha may play an important role in the progression of arteriosclerosis. Antioxidant treatment may promise significant clinical benefits in the early diabetic stage.

Troglitazone ameliorates abnormal activity of protein tyrosine phosphatase in adipose tissues of Otsuka Long-Evans Tokushima Fatty rats.

Protein tyrosine phosphatases (PTPases) play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin signaling pathway. To determine the role of PTPases in adipose tissue in the development into an insulin-resistant state, we examined PTPase activities and protein levels of three major candidate PTPases in adipose tissues of 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Particulate PTPase activities in visceral and epididymal adipose tissues of OLETF rats were increased compared to those in Long-Evans Tokushima Otsuka (LETO) rats, non-insulin-resistant controls. Cytosolic PTPase activities in these tissues were conversely decreased in OLETF rats. In subcutaneous adipose tissues, those changes were not observed. Western blot analysis showed that the amounts of leukocyte antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2) were increased in particulate fractions of visceral and epididymal fat of OLETF rats. On the other hand, those in the cytosolic fractions were slightly decreased. Troglitazone was administered to OLETF rats to examine the effect of the drug on the changes in PTPase activity and distribution. Troglitazone treatment restored those alterations in PTPase activity in the particulate fraction and the amounts of LAR, PTP1B and SH-PTP2 in both fractions of visceral and epididymal adipose tissues of OLETF rats. Although it remains unknown whether such effects of troglitazone are mediated by peroxisome proliferator-activated receptor y, these data provide useful information for understanding the significance of PTPase in insulin-resistant rats and the molecular mechanism of troglitazone action.

Retinal and Choroidal Vasculature in Rats with Spontaneous Diabetes Type 2 Treated with the Angiotensin-Converting Enzyme Inhibitor Cilazapril: Corrosion Cast and Electron-Microscopic Study

The long-term effects of the angiotensin-converting enzyme (ACE) inhibitor cilazapril on retinal and choroidal circulation in rats with spontaneous diabetes type 2 were assessed by corrosion casts, scanning electron microscopy (SEM) and transmission electron microscopy. One group of 20 male Otsuka Long-Evans Tokushima Fatty (OLETF) rats was treated with 10 mg/kg/day of cilazapril from 4 to 64 weeks of age, and 20 other OLETF rats received no treatment. A third group, 20 male Long-Evans Tokushima Otsuka (LETO) rats, served as age-matched controls. At regular intervals, the rats were weighed, and their blood glucose was measured. Before the experiment, their systolic blood pressure and total cholesterol level were determined. At 64 weeks of age, the OLETF rats weighed significantly less than the cilazapril-treated OLETF and the LETO rats (p < 0.0001). At the same age, 100% of the untreated OLETF rats had bilateral cataracts, while the lens was clear and no fundus abnormality was detected in the cilazapril-treated OLETF rats and the LETO rats. Cilazapril lowered systolic blood pressure to a nearly normal level, significantly prevented the increase in blood sugar and inhibited the increase in serum cholesterol in the OLETF rats throughout the treatment. In the 64-week-old OLETF rats without treatment, corrosion cast and SEM revealed diabetic retinal and choroidal vascular changes: tortuosity of the vessels, variations in caliber, narrowing of arteries, arterio-arteriolar anastomoses and hairpin loop formation in precapillary arterioles, sparse collecting venules in the choroid and marked capillary changes such as caliber irregularity, narrowing, tortuosity, loop formation and decreased capillaries, outpouching and microaneurysms. In the cilazapril-treated OLETF rats, these changes were markedly decreased to the level seen in the LETO rats, in which the retinal and choroidal blood vessels had a definite and fairly constant pattern and the capillaries were more regularly and densely arranged and had a remarkably uniform caliber. Our results show that the long-term administration of cilazapril before or from the initial onset significantly prevented the increase in blood sugar and inhibited the increases in serum cholesterol in OLETF rats throughout the treatment, lowered systolic arterial pressure to a nearly normal level and prevented diabetic ocular complications. The effects of cilazapril on the diabetic retinal and choroidal vasculature are described for the first time. SEM of corrosion casts is a valuable and easy technique for showing precisely and three-dimensionally the effects of some drugs on the vasculature.

Growth-Related Changes in Skeletal Muscle Fiber Type and Insulin Resistance in Diabetic Otsuka Long-Evans Tokushima Fatty Rats.

We investigated whether a relationship exists between the fiber type distribution in skeletal muscles and the insulin resistance of different ages of diabetic rats. The fiber type distributions of the slow soleus and fast plantaris muscles in 5-, 9-, and 21-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats as an animal model of spontaneous type 2 diabetes mellitus were examined and compared with those in age-matched non-diabetic Long-Evans Tokushima Otsuka (LETO) rats. In the soleus muscle, a higher percentage of type I fibers was observed in the 9- and 21-week-old OLETF rats compared with the age-matched LETO rats, and there were no type IIA fibers remaining in the soleus muscle of the OLETF rats. In the plantaris muscle, a lower percentage of type IIA fibers and a higher percentage of type IIB fibers were observed in the 9- and 21-week-old OLETF rats compared with the age-matched LETO rats. In addition, a lower percentage of type I fibers in the plantaris muscle was observed in the 9-week-old OLETF rats compared with the age-matched LETO rats, and there were no type I fibers in the plantaris muscle of the 21-week-old OLETF rats. All 20-week-old OLETF rats showed serum insulin concentrations of more than 20 ng/ml. The present study suggests that insulin resistance and impaired glucose tolerance from altered muscle fiber type are linked to the cause of diabetes.

Evaluation of the cardiac autonomic nervous system in spontaneously non-insulin-dependent diabetic rats by 123I-metaiodobenzylguanidine imaging.

To evaluate the sensitivity of 123I-labeled metaiodobenzylguanidine (123I-MIBG) scintigraphy in detecting diabetic autonomic nervous system disorders. Thirty-one-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of spontaneous non-insulin-dependent diabetes mellitus, were maintained for 8 weeks with or without 30% sucrose solution as a drinking water (n = 3 each). Long-Evans Tokushima Otsuka (LETO) rats (n = 3), served as controls. Plasma glucose and insulin levels were measured, and 123I-MIBG scintigraphy was performed with a gamma camera equipped with a pinhole collimator for animals. Plasma and cardiac tissue cathecolamine levels were also determined. Plasma glucose levels of OLETF rats with and without sucrose loading (554+/-106 and 141+/-1.5 mg/dl respectively) were significantly higher than those of LETO rats (116+/-3.7 mg/dl). Norepinephrine concentrations in heart and plasma tended to be lower in diabetic rats. The washout rate of 123I-MIBG in diabetic rats was significantly higher than the rate in control rats. Cardiac uptake of 123I-MIBG, calculated as % dose/g of tissue, was significantly lower in diabetic rats than in control rats. These results suggest that myocardial 123I-MIBG scintigraphy is suitable for assessing cardiac sympathetic activity noninvasively in diabetic states, even in the early stages.

Alterations of insulin and glucagon secretion from the perfused pancreas before, at the onset and after the development of diabetes in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an obese non-insulin dependent diabetes mellitus (NIDDM) model of an inbred strain. In this study, basal (2.8 mM glucose) insulin and glucagon and their responses to glucose (16.7 mM) were examined at the age of 9 weeks ( n=3) before the onset of diabetes, at 23 weeks ( n=6) at the onset of diabetes, and at 48 weeks ( n=5) after the development of diabetes by pancreatic perfusion. In Long-Evans Tokushima Otsuka (LETO, control) rats, insulin responses to glucose showed a biphasic pattern at all three ages, while in OLETF rats, basal insulin concentrations were significantly increased compared to those in controls at the age of 9 and 48 weeks. Insulin responses to glucose showed no difference from controls at 9 and 23 weeks, however, at 48 weeks the response was significantly decreased. In controls, high basal glucagon concentrations showed significant decrease in response to glucose at all ages. In OLETF rats, basal glucagon concentrations showed significant decrease compared to those in control rats at 23 and 48 weeks. Glucagon response to glucose significantly decreased at 9 and 23 weeks, but at 48 weeks there was no change in concentration in response to glucose. Pancreatic insulin content was lower at 48 weeks in OLETF rats than in LETO rats, although no differences were observed at other ages. There were no significant differences in pancreatic glucagon content between the two groups at any age. Morphologically, in OLETF rats the number of pancreatic B cells were decreased and A cells migrated into the center of islets at 48 weeks. The results suggested that one of the causes of diabetes in OLETF rats is impaired insulin response to glucose.

Plasma membrane content of insulin-regulated glucose transporter in skeletal muscle of the male Otsuka Long-Evans Tokushima Fatty rat, a model of non-insulin-dependent diabetes mellitus

The male Otsuka Long-Evans Tokushima Fatty (OLETF) rat shows insulin resistance in skeletal muscle and visceral obesity. To obtain information on the mechanism of the insulin resistance in the diabetic rats, we examined the content of insulin-regulated glucose transporter (GLUT4) in skeletal muscles. The results indicate that the total content of the transporter is significantly decreased ( P<0.05) in muscles of the diabetic rats. Plasma membrane content of the GLUT4 protein in muscles of the diabetic rats was increased in the basal state as compared to control rats. Hyperinsulinemic clamps increased GLUT4 levels in the plasma membrane of control rats but failed to do so in the diabetic rats. The distribution of GLUT4 in OLETF rat is reminiscent of the characteristics of human non-insulin-dependent diabetes mellitus.