Chronic Alcohol Consumption Results in Greater Damage to the Pancreas Than to the Liver in the Rats

Alcohol consumption increases the risk of type 2 diabetes. However, its effects on prediabetes or early diabetes have not been studied. We investigated endoplasmic reticulum (ER) stress in the pancreas and liver resulting from chronic alcohol consumption in the prediabetes and early stages of diabetes. We separated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type-2 diabetic animal model, into two groups based on diabetic stage: prediabetes and early diabetes were defined as occurrence between the ages of 11 to 16 weeks and 17 to 22 weeks, respectively. The experimental group received an ethanol-containing liquid diet for 6 weeks. An intraperitoneal glucose tolerance test was conducted after 16 and 22 weeks for the prediabetic and early diabetes groups, respectively. There were no significant differences in body weight between the control and ethanol groups. Fasting and 120-min glucose levels were lower and higher, respectively, in the ethanol group than in the control group. In prediabetes rats, alcohol induced significant expression of ER stress markers in the pancreas; however, alcohol did not affect the liver. In early diabetes rats, alcohol significantly increased most ER stress-marker levels in both the pancreas and liver. These results indicate that chronic alcohol consumption increased the risk of diabetes in prediabetic and early diabetic OLETF rats; the pancreas was more susceptible to damage than was the liver in the early diabetic stages, and the adaptive and proapoptotic pathway of ER stress may play key roles in the development and progression of diabetes affected by chronic alcohol ingestion.

Reduction of Food Intake by Fenofibrate is Associated with Cholecystokinin Release in Long-Evans Tokushima Rats

Fenofibrate is a selective peroxisome proliferator-activated receptor alpha (PPARalpha) activator and is prescribed to treat hyperlipidemia. The mechanism through which PPARalpha agonists reduce food intake, body weight, and adiposity remains unclear. One explanation for the reduction of food intake is that fenofibrate promotes fatty acid oxidation and increases the production of ketone bodies upon a standard experimental dose of the drug (100~300 mg/kg/day). We observed that low-dose treatment of fenofibrate (30 mg/kg/day), which does not cause significant changes in ketone body synthesis, reduced food intake in Long-Evans Tokushima (LETO) rats. LETO rats are the physiologically normal controls for Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which are obese and cholecystokinin (CCK)-A receptor deficient. We hypothesized that the reduced food intake by fenofibrate-treated LETO rats may be associated with CCK production. To investigate the anorexic effects of fenofibrate in vivo and to determine whether CCK production may be involved, we examined the amount of food intake and CCK production. Fenofibrate-treated OLETF rats did not significantly change their food intake while LETO rats decreased their food intake. Treatment of fenofibrate increased CCK synthesis in the duodenal epithelial cells of both LETO and OLETF rats. The absence of a change in the food intake of OLETF rats, despite the increase in CCK production, may be explained by the absence of CCK-A receptors. Contrary to the OLETF rats, LETO rats, which have normal CCK receptors, presented a decrease in food intake and an increase in CCK production. These results suggest that reduced food intake by fenofibrate treatment may be associated with CCK production.

Ultrastructural Investigation of the Retinal Changes in Diabetic Rat (OLETF)

PURPOSE: To compare retinal ultra-structures of diabetic rats (OLETF, Otsuka Long-Evans Tokushima Fatty) with those of agematched non-diabetic rats (LETO, Long-Evans Tokushima Otsuka) using transmission electron micrography (TEM). METHODS: The body weights and blood sugar levels of the OLETF rats and LETO rats (n=5) were measured at 10 and 50 weeks of age. Using a TEM, we compared the ultra-structural changes between the retinas of the 50-week-old OLETF and LETO rats. We analyzed the sizes of the pericytes and the thicknesses of the retinal capillary basement membranes between the two groups. Comparisons were made using a Scion Image(R). RESULTS: The mean body weight and blood sugar levels of the 50-week-old OLETF rats were significantly higher than those of the LETO rats (p(R)0.05). The thicknesses of the retinal capillary basement membranes in the outer plexiform layer and the size of pericytes were significantly increased in the OLETF rats at 50 weeks of age (p<0.05). The number of nuclei in the inner nuclear layer and the outer nuclear layer (photoreceptor cell nuclei) significantly decreased (p<0.05). However, the height of the RPE cells and basal in-foldings showed no significant differences between the OLETF and LETO rats. CONCLUSIONS: The retinal changes in the OLETF rats were observed relatively early at 50 weeks of age. These changes are similar to those seen in human diabetic retinopathy. Change in the capillaries is one feature of early retinal change. OLETF rats may be a useful animal model in NIDDM to examine diabetic retinal changes.

Effect of 17-beta Estradiol on Adipocyte Lipin-1 Expression in OLETF Rat

BACKGROUND: 17 beta-estradiol is known to play an important role in glucose homeostasis. Lipin-1 is a nuclear protein that is essential in adipocyte differentiation and it is considered to play a role in ectopic fat deposition and the redistribution of fat. The aim of this study was to evaluate the effect of 17 beta-estradiol on the lipin-1 expression in the adipocytes of OLETF rats, which is an animal model of diabetes. METHODS: The OLETF rats were divided into 3 groups, 1) the sham-operation group (SHAM) 2) the castrated group (CAST) and 2) the castrated and estradiol treatment group (EST), and all the rats were at 6 weeks of age. LETO rats were used as a control group (LETO). 0.1 mg of estradiol valerate was injected subcutaneously every 4 weeks in the rats of the EST group. The visceral and subcutaneous tissues were isolated to evaluate the lipin-1 protein expression. The lipin-1 expression was measured in human visceral and subcutaneous preadipocytes. RESULTS: Less body weight gain was observed in the EST group compared with that of the SHAM group. In addition, improvement in the glucose tolerance was observed in the EST group. The lipin-1 expression in visceral fat was decreased in the SHAM and CAST groups, but it was but recovered in the EST group. The lipin-1 expression in the subcutaneous fat was decreased in the SHAM, CAST, and EST groups. CONCLUSION: Long term estradiol treatment in OLETF rats reduces the body weight gain and improves the glucose tolerance. Estradiol enhances the lipin-1 protein expression in the visceral adipocytes, but not in the subcutaneous adipocytes.

Metformin down-regulates the expression of regulators of G protein signaling in OLETF rats / 中国糖尿病杂志

Objective To investigate the expression of regulators of G protein signaling(RGS), including RGS2, RGS3 and RGS4 in OLETF rats, as well as the effects of metformin on these expressions. Methods LETO rats were used as control group. Eight-week-old male OLETF rats were assigned to two guoups randomly:model and trial(metfomin dose during 8~(th) to 22~(nd) weeks:300mg kg~(-1)·d~(-1);during 23rd to 28th weeks:400 mg·kg~(-1) ·d~(-1))groups. Expressions of RGS mRNA in aorta and heart werequantified by real-time PCR. Results RGS2, RGS3 and RGS4 mRNA of the thoracic aorta and left ventricle were significantly higher in model group than in control group (P<0.01). Compared with model group, metformin significantly reduced their mRNA in trial group (P<0.01). Conclusions Upregulation of RGS2, RGS3 and RGS4 mRNA expression in the thoracic aorta and left ventricle of OLETF rats is in correlation with cardiovascular lesions; while downregulation of their expression is in correlation with the action of metformin.

The Effect of Pioglitazone on the Expression of Transforming Growth Factor (TGF)-beta and Fibronectin in Diabetic Nephropathy / 대한신장학회잡지

BACKGROUND: Peroxisome proliferator-activated receptor (PPAR)-gamma is a member of the nuclear receptor superfamily. PPAR-gamma plays an important role in numerous cellular processes including adipogenesis, insulin sensitivity, cell cycle progression, cell differentiation, inflammation, and extracellular matrix production. This study investigated the effect of a PPAR-gamma agonist on the progression of diabetic nephropathy in OLETF rats. METHODS: 30 week-old male OLETF rats were treated for 10 weeks as follows:diabetic control (DM), no treatment:pioglitazone therapy (DM+Pio). LETO rats were used as non-diabetic control (control). Body weight, blood pressure, blood sugar, creatinine, total cholesterol, triglyceride, and urinary protein excretion were measured. Histological analysis was taken with light microscope. Glomerular protein and mRNA expression of transforming growth factor (TGF)-beta1 and fibronectin were estimated by Western blot and RT-PCR. Kidney sections were stained for fibronectin by immunohistochemistry. RESULTS: Serum glucose, triglyceride and urinary protein excretion were decreased in DM+Pio rats compared to DM rats (p<0.05). PAS staining showed glomerular hypertrophy, mesangial expansion, nodular sclerosis, and glomerular basement membrane thickening in glomeruli of DM rats, but these changes were attenuated in glomeruli of pioglitazone-treated rats. Treatment with pioglitazone resulted in a significant decrease in TGF-beta1 protein and mRNA expression in diabetic glomeruli (80.6% and 78.4%, respectively). Glomerular expression of fibronectin protein and mRNA were also decreased in pioglitazone treatment group compared with DM group (93.1% and 98.6%, respectively). Immunohistochemical staining for fibronectin showed similar results. CONCLUSION: Increased TGF-beta1 and fibronectin mRNA and protein expressions in diabetic rat glomeruli were significantly ameliorated by pioglitazone treatment. These data suggest that activation of PPAR-gamma may play an important role in prevention and treatment of diabetic nephropathy.

Erectile Function and Cavernosal TGF-beta Expression in the OLETF Rats / 대한남성과학회지

PURPOSE: The mechanism of erectile dysfunction in type II non-insulin dependent diabetes mellitus (NIDDM) has not been well demonstrated. The aims of this study were to investigate erectile function and cavernosal TGF-beta expression in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which develop NIDDM naturally. MATERIALS AND METHODS: Twenty male OLETF rats and ten control LETO rats were included in this study. After 30 weeks, blood glucose levels and body weights were measured. Systemic arterial pressure and intracavernosal pressure were measured before and after pelvic nerve stimulation. Cross sections of the penis were processed for histologic and immunohistochemistry examinations. RESULTS: The mean body weights and mean blood glucose levels were significantly higher in the OLETF group (645.0 40.0 g; 130.8 55.6 mg/ml) compared to control group (538.0 14.4 g; 84.1 14.7 mg/ml), respectively (p<0.05). Nerve stimulation-induced peak intracavernosal pressure (mmHg) was significantly decreased in the OLETF group (41.3 15.4 mmHg) compared to control group (83.3 15.8 mmHg) (p<0.05). In the OLETF rats, the collagen connective tissue in the corpus cavernosum showed a dense and irregular arrangement. The immunoreactivity for TGF-beta 1 was prominent in collagen fibers, fibroblast and smooth muscle in the OLETF rats. CONCLUSIONS: In this study, OLETF rats showed significantly decreased erectile function compared with control rats, and histologic examination revealed cavernosal fibrosis and increased TGF-beta 1 expression. These results imply that the OLETF rat may be a good model to study the mechanism of erectile dysfunction in NIDDM.