Otsuka Long-Evans Tokushima Fatty Strain Research Articles

PS-BPC06-5: EXOGENOUS THYROXINE INCREASES GLUT4 TRANSLOCATION IN MEMBRANE AND IMPROVES CARDIAC METABOLISM INDEPENDENT OF REDUCED SBP IN INSULIN RESISTANT OLETF RATS

Objective: During insulin resistance the heart undergoes a metabolic shift where fatty acids (FA) account for about 99% of the ATP production, indicative of impaired glucose metabolism. This results in increased reactive oxygen species and lipotoxicity leading to impaired mitochondrial function. Thyroid disorders such as hyperthyroidism and hypothyroidism both have the potential to lead to hypertension. Thyroid hormones (TH) may improve glucose intolerance by increasing glucose reabsorption and metabolism and therefore improve cardiac function and lower the risk of developing hypertension. However, incongruent data exists showing that TH promote oxidative stress and cardiac hypertrophy. Thus, the beneficial effects of TH in the heart during insulin resistance remains controversial. The glucose transport protein, GLUT4, is a downstream target of the TH response element indicating a possible mechanism by which TH regulate glucose metabolism. Design: Insulin resistant, Otsuka Long Evans Tokushima Fatty (OLETF) rats were used to assess the effects of exogenous thyroxine (T4) on glucose metabolism in cardiac tissue. Rats were assigned to four groups: 1) lean, Long Evans Tokushima Otsuka (LETO; n = 6), 2) LETO + T4 (8 μg/100 g BM/d × 5 wks; n = 7), 3) untreated OLETF (n = 6), and 4) OLETF + T4 (n = 7). T4 was administered via osmotic minipumps implanted subcutaneously. Systolic blood pressure (SBP) was measured weekly in conscious rats by tail-cuff plethysmography. Animals were provided water and food ad libitum. Results: SBP increased by 15% in OLETF compared to lean LETO (138 ± 2 vs. 117 ± 1 mm Hg), but T4 did not alter SBP is OLETF strain. T4 increased GLUT4 gene expression by 85% and GLUT4 protein translocation to the membrane by 328% in OLETF. Additionally, T4 increased phosphofructokinase-1, the rate limiting step in glycolysis, by 98% and decreased CD36 gene expression for FA transport by 20% in OLETF. We expect our recent metabolomics and lipidomics data to help better explain these molecular changes. Conclusions: Five-week dose of exogenous T4 did not reduce SBP is OLETF. The results suggest that increased T4 has the potential to increase glucose reabsorption and metabolism in the heart of insulin resistant rats and restore impaired substrate metabolism, but these improvements in substrate metabolism do not translate to sustained reduction in arterial pressure.

Cocaine- and amphetamine-regulated transcript (CART) peptide immunoreactivity in feeding- and reward-related brain areas of young OLETF rats

Cocaine- and amphetamine-regulated transcript (CART) peptide is expressed in brain areas involved in the control of appetite, drug reward and homeostatic regulation and it has an overall anorexigenic effect. Recently, we have shown that CART peptide immunoreactivity was significantly reduced in the rostral part of the nucleus accumbens and in the rostro-medial part of the nucleus of the solitary tract in adult CCK-1 receptor deficient obese diabetic Otsuka Long Evans Tokushima Fatty (OLETF) rats compared to Long Evans Tokushima Otsuka (LETO) lean controls. It is not clear, however, whether altered CART expression is caused primarily by the deficiency in CCK-1 signaling or whether is related to the obese and diabetic phenotype of the OLETF strain which develops at a later age. Therefore, in the present study, CART-immunoreaction in feeding-related areas of the brain was compared in young, age-matched (6–7 weeks old) non-obese, non-diabetic OLETF rats and in LETO controls. We found that, young, non-diabetic OLETF rats revealed unaltered distribution of CART-peptide expressing neurons and axons throughout the brain when compared to age-matched LETO rats. In contrast to previous results observed in the obese diabetic adult rats, intensity of CART immunoreaction did not differ in the areas related to control of food-intake and reward in the young OLETFs compared to young LETO rats. Our findings suggest that factors secondary to obesity and/or diabetes rather than impaired CCK-1 receptor signaling may contribute to altered CART expression in the OLETF strain.

Anxiety-like behavior and locomotion in CCK 1 knockout rats as a function of strain, sex and early maternal environment

CCK is a peptide broadly distributed in the brain that is involved in the regulation of emotional behaviors through its binding to CCK 1 and CCK 2 receptors. Research has shown altered emotional and activity phenotypes in (male) Otsuka Long Evans Tokushima Fatty (OLETF) rats that lack CCK 1 receptors. In the present study, we examined anxiety-like behaviors, locomotion and corticosterone levels in OLETF and control (Long Evans Tokushima Otsuka (LETO)) strains (Experiment 1), and after cross-fostering and in-fostering conditions (Experiment 2), in males and females. The aim was to examine the early maternal contribution to the offspring's behaviors as examined in the elevated plus-maze and open-field paradigms. The results suggest a genetic/prenatal predisposition to moderate anxiety-like behaviors in the OLETF strain, especially in the males. Cross-fostering OLETF females to LETO dams significantly improved their performance both in the open field and the elevated plus maze. Hypo-locomotion was evident in OLETF rats of both sexes and remained unchanged regardless of the rearing conditions. LETO rats’ behavior was not affected by cross-fostering. Basal corticosterone levels remained similar among all groups at weaning and adulthood. The improvement in the OLETF strain's overall performance after adoption suggests a maternal contribution to the altered phenotype of these rats. The findings demonstrated the contribution of genetics, sex and early maternal environment to anxiety-like behaviors and locomotion in CCK 1 knockout rats, suggesting in addition to locomotion-reduction, the mutation may predispose the animals (rather than directly induce) to a moderate anxious phenotype.

Development of obesity in the Otsuka Long-Evans Tokushima Fatty rat

Understanding the early factors affecting obesity development in males and females may help to prevent obesity and may lead to the discovery of more effective treatments for those already obese. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat model of obesity is characterized by hyperphagia-induced obesity, due to a spontaneous lack of CCK(1) receptors. In the present study, we focused on the behavioral and physiological aspects of obesity development from weaning to adulthood. We examined body weight, feeding efficiency, fat pad [brown, retroperitoneal, inguinal and epydidimal (in males)] weight, inguinal adipocyte size and number, leptin and oxytocin levels, body mass index, waist circumference, and females' estrous cycle structure. In the males, central hypothalamic gene expression was also examined. OLETF rats presented overall higher fat and leptin levels, larger adipocytes, and increased waist circumference and BMI from weaning until adulthood, compared with controls. Analysis of developmental patterns of gene expression for hypothalamic neuropeptides revealed peptide-specific patterns that may underlie or be a consequence of the obesity development. Analysis of the developmental trajectories toward obesity within the OLETF strain revealed that OLETF females developed obesity in a more gradual manner than the males, presenting delayed obesity-related "turning points," with reduced adipocyte size but larger postweaning fat pads and increased adipocyte hyperplasia compared with the males. Intake decrease in estrus vs. proestrus was significantly less in OLETF vs. Long-Evans Tokushima Otsuka females. The findings highlight the importance of using different sex-appropriate approaches to increase the efficacy of therapeutic interventions in the treatment and prevention of chronic early-onset obesity.

Microstructural pattern of palatable food intake from weaning to adulthood in male and female OLETF rats.

Ontogenetic trajectories from weaning to adulthood and sex differences in feeding patterns were examined in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of early onset overeating-induced obesity, and a natural cholecystokinin-1 receptor knockout. Overnight patterns of licking a palatable liquid diet (Ensure) were analyzed on Postnatal Days 22, 38, 60, and 90. Because different microstructure profiles may reflect alterations in the influence of positive and negative signals, we examined meal parameters to uncover developing mechanisms underlying eating behavior in this strain. OLETF rats displayed significantly greater caloric intake, larger meals (in number of licks), and more (within-meal) clusters of feeding (which were shorter in duration and contained fewer licks per cluster) than did Long-Evans Tokushima Ohtsuka (LETO) strain controls. OLETF rats also had significantly lower satiety ratios than LETO rats. Moreover, we identified sex differences in the age of emergence of microstructural patterns of obesity-related overeating, suggesting that systems other than cholecystokinin may be disrupted, possibly worsening the OLETF strain's obesity phenotype.

Toward an animal model of childhood-onset obesity: follow-up of OLETF rats during pregnancy and lactation

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat model of obesity (a spontaneous CCK1 receptor knockout) has been extensively studied as model of hyperphagia-induced obesity. In previous studies, young OLETF rats presented abnormal eating patterns [compared with Long-Evans Tokushima Otsuka (LETO) controls] in a variety of independent ingestion and nursing tests during the suckling period. The aim of the present study was to characterize the early emergence of abnormal adiposity in the pups. Moreover, because both the dams and the pups present the genetic mutation, a close follow-up of the dams' body weight and intake during pregnancy and lactation was performed to examine the circumstances that contribute to build up the pups' early adiposity. Compared with controls, OLETF pups presented higher fat levels, larger adipocytes, and increased waist circumference as early as postnatal day 7 and this profile persisted to the age of weaning. While LETO dams gained weight throughout pregnancy and lactation, OLETF dams were obese and hyperphagic during pregnancy but lost weight during lactation, probably as a result of rearing hyperphagic pups. Current and previous results suggest a possible influence of the dams' obesity during gestation and a high investment in nursing time during lactation on the pups' obesity levels during childhood. This, combined with the innate hyperphagia repeatedly observed in the pups at these early ages, makes the OLETF strain a useful tool in the research of childhood-onset obesity.

MUTATED G‐PROTEIN‐COUPLED RECEPTOR GPR10 IS RESPONSIBLE FOR THE HYPERPHAGIA/DYSLIPIDAEMIA/OBESITY LOCUS OF Dmo1 IN THE OLETF RAT

1. We have confirmed the Diabetes Mellitus OLETF type I (Dmo1) effect on hyperphagia, dyslipidaemia and obesity in the Otsuka Long-Evans Tokushima Fatty (OLETF) strain. The critical interval was narrowed down to 570 kb between D1Got258 to p162CA1 by segregation analyses using congenic lines. 2. Within the critical 570 kb region of the Dmo1 locus, we identified the G-protein-coupled receptor gene GPR10 as the causative gene mutated in the OLETF strain. The ATG translation initiation codon of GPR10 is changed into ATA in this strain and, so, is unavailable for the initiation of translation. 3. The GPR10 protein has a cognate ligand, namely prolactin-releasing peptide (PrRP). Centrally administered PrRP suppressed the food intake of congenic rats that have a Brown Norway derived Dmo1 region (i.e. with wild-type GPR10), but did not suppress that of the OLETF strain, indicating that GPR10 is without function and could explain hyperphagia in the OLETF strain. 4. Moreover, when restricted in food volume to the same level consumed by the congenic strain, OLETF rats showed few differences in the parameters of dyslipidaemia and obesity compared with congenic strains. 5. Taken together, these results demonstrate that the mutated GPR10 receptor is responsible for the hyperphagia leading to obesity and dyslipidaemia in the obese diabetic strain rat.

Gonadal Hormones and Gonadal Function in Type 2 Diabetes Model OLETF (Otsuka Long Evans Tokushima Fatty) Rats

Gonadal functions, with special reference to blood levels of sex-related markers such as 17beta-estradiol (E2), free testosterone (free Te) and lutenizing hormone (LH), were examined in male OLETF (Otsuka Long Evans Tokushima Fatty) diabetic rats, a model of human type 2 diabetes mellitus. Male rats of the OLETF strain and male rats of the LETO strain, which act as a control of OLETF, both supplied by Otsuka Pharmaceutical Co., Ltd. (Tokushima, Japan), were periodically examined for blood levels of E2, free Te and LH at the age of 4, 5, 32, 40 and 64 weeks. The weight of the testis, the number of sperm contained within and histological findings of the testis were comparatively studied in both strains. Glucose and insulin (IRI) at fasting were examined to evaluate the homeostasis model assessment (HOMA) index. In order to investigate any sex hormone imbalance, sex hormone-binding globulin (SHBG) was measured by a dextran- charcoal assay. All of the OLETF rats became diabetic at the age of 32 weeks. There were no significant differences between OLETF and LETO rats regarding free Te, E2, LH or SHBG during the observation period from 4 to 64 weeks. Testis weight was significantly decreased in OLETF rats at 32 and 64 weeks and sperm counts at 64 weeks of age were also significantly decreased. Histologically, there was seminiferous tubule atrophy in the OLETF rats at 64 weeks of age. A significant negative correlation between testis weight and fasting blood glucose, as well as HOMA index, was observed in OLETF rats. In male diabetic OLETF rats, with a variety of hypogonadisms such as atrophy of the testis and low sperm count, the serum levels of E2, free Te, LH and SHBG were normally preserved.

A < 1.7 cM interval is responsible for Dmo1 obesity phenotypes in OLETF rats

1. Dmo1 (Diabetes Mellitus OLETF type I) is a major quantitative trait locus for dyslipidaemia, obesity and diabetes phenotypes of male Otsuka Long Evans Tokushima Fatty (OLETF) rats. 2. Our congenic lines, produced by transferring Dmo1 chromosomal segments from the non-diabetic Brown Norway (BN) rat into the OLETF strain, have confirmed the strong, wide-range therapeutic effects of Dmo1 on dyslipidaemia, obesity and diabetes in the fourth (BC4) and fifth (BC5) generations of congenic animals. Analysis of a relatively small number of BC5 rats (n = 71) suggested that the critical Dmo1 interval lies within a < 4.9 cM region between D1Rat461 and D1Rat459. 3. To confirm the assignment of the Dmo1 critical interval, we intercrossed BC5 animals to produce a larger study population (BC5:F1 males; n = 406). For the present study, we used bodyweight at 18 weeks of age as an index of obesity; this phenotype is representative of the closely associated dyslipidaemia and hyperglycaemia phenotypes. 4. Interval mapping assigned logarithm of odds (LOD) peaks at the D1Rat90 marker (LOD = 9.11). One LOD support interval lies within the < 1.7 cM region between D1Rat461 and D1Rat459. 5. This large intercross study confirms that Dmo1 is likely localized within the interval.

Role for thromboxane A 2 from glomerular thrombi in nephropathy with type 2 diabetic rats

We used rats (the Otsuka Long-Evans Tokushima Fatty strain) as a model of type 2 diabetes to find whether thromboxane (TX) A 2 is involved in diabetic nephropathy, and if so, to identify where it is synthesized. We measured urinary excretion of TXB 2 and 2,3-dinor-TXB 2 in rats up to 60 weeks of age as markers of renal and platelet synthesis of TXA 2, respectively. Some diabetic rats were given daily oral doses of OKY-046 (100 mg/kg), a TXA 2 synthase inhibitor, starting when they were 10 weeks of age. Healthy Long-Evans Tokushima Otsuka rats served as the controls. Urinary excretion of protein was greater in diabetic rats at 26 weeks than in controls, and the difference increased with age. Urinary excretion of TXB 2 by diabetic rats was about 150% that of controls at 14 weeks, and remained at that level. In diabetic rats, urinary excretion of 2,3-dinor-TXB 2 increased with age in parallel to increases in proteinuria, but in controls, excretion of these metabolites did not change with age. In diabetic rats, OKY-046 prevented the increase in urinary excretion of both metabolites, and decreased the proteinuria. Histologic examination at 60 weeks showed intraglomerular thrombi in diabetic rats but not in controls. OKY-046 reduced intraglomerular thrombi formation and the score for glomerulosclerosis. When platelet aggregation began, more TXA 2 than before was released from the thrombi that formed, and the TXA 2 contributed to the progress of nephropathy in this rat model of type 2 diabetes.

Genetic analysis of pancreatic duct hyperplasia in Otsuka Long-Evans Tokushima Fatty rats: possible association with a region on rat chromosome 14 that includes the disrupted cholecystokinin-A receptor gene.

An Otsuka Long-Evans Tokushima Fatty (OLETF) strain of rat spontaneously developed hyperglycemia, hyperinsulinemia, insulin resistance and mild obesity, which had been studied as animal model for type II diabetes mellitus (T2DM). Recently, we observed that this strain coincidentally developed atypical hyperplasia of the choledocho-pancreatic ductal epithelium with a complete incidence. In an effort to locate genes responsible for this hyperplasia, we prepared 288 backcross progeny from a mating between OLETF rats and BN rats (which do not develop hyperplasia), and performed a genome-wide scan using 207 polymorphic genetic markers. We observed a prominent association of hyperplasia with a region involving a marker locus D14Mit4 (P = 0.00020, Fisher's exact test) and Cckar (the cholecystokinin-A receptor gene; P = 0.00025, Fisher's exact test) which is known to be disrupted in an OLETF strain. Our findings indicated that epithelial hyperplasia of the choledocho-pancreatic duct is associated with a region on rat chromosome 14 around the Cckar gene in an additive fashion with another two susceptible loci, each on chromosome 9 and 7. This implied the possibility that Cckar deficiency could result in a predisposition towards pancreatic duct hyperplasia.

Renal production of thromboxane and prostaglandins in a rat model of type 2 diabetes

In an investigation of the involvement of prostanoids in the pathogenesis of nephropathy in type 2 diabetes, we repeatedly measured the urinary excretion of prostanoids in both diabetic and healthy rats as the rats aged. Seven rats of the Otsuka Long-Evans Tokushima Fatty strain were used as rats with a model of type 2 diabetes and seven rats of the Long-Evans Tokushima Otsuka strain were used as rats without diabetes. Thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1α, the amounts of which reflect renal production of TXA2 and PGI2, respectively, and PGE2 in urine collected in metabolic cages were assayed when rats were 14, 30, 46, and 54 weeks old. Plasma glucose and urinary protein excretion also were measured periodically. The mean plasma glucose concentration of the diabetic rats was higher than that of the healthy rats throughout the study. At 30 weeks and later, urinary protein excretion by the diabetic rats was greater than that of the healthy rats, and it increased with age. Urinary excretion of TXB2 by the diabetic rats was higher than that of the healthy rats at 14 weeks (52.4 ± 23.5 vs. 27.0 ± 2.6 ng/day; mean ± SD, P = .015) and the difference continued to the end of the experiment. Urinary excretion of 6-keto-PGF1α by the diabetic rats was high at 14 weeks (52.3 ± 12.8 vs. 26.9 ± 4.6 ng/day; mean ± SD, P < .001) but decreased with age and was the same as that of the healthy rats at 54 weeks. The urinary excretion of PGE2 by the two groups of rats was not significantly different. These results suggest that altered renal production of TXA2 and PGI2 is involved in the pathogenesis of diabetic nephropathy in rats with type 2 diabetes.

Ethanol ingestion combined with lowered carbohydrate (sucrose) intake aggravates diabetes mellitus in spontaneously diabetic rats

The effects of ethanol ingestion on the development of diabetes mellitus were studied in relation to simultaneous carbohydrate intake. We used sucrose as a carbohydrate source. Two groups of spontaneously diabetic (non-insulin dependent type) male rats (Otsuka Long-Evans Tokushima Fatty Strain, OLETF) at 10 weeks of age were fed liquid diets containing ethanol (4.0 g/day) with different amounts of sucrose (6.8 or 13.8 g/day) in 100 ml solution for 20 weeks. Two other groups of the same strain were studied. One was kept to be fed a liquid diet containing sucrose (13.8 g/day) without ethanol in 100 ml solution and the other was given free access to solid chow and water and served as a control group. Each of the four groups had 10 rats. The three liquid diets were the same except for ethanol and sucrose content and contained adequate amounts of protein, fat, vitamins and minerals. Shortly after the start of experimental feeding (12 weeks of age), an oral glucose tolerance test (OGTT) showed no abnormalities in any groups. However, at the end of the experiment (30 weeks of age), almost all the rats were diabetic. The severity of diabetes mellitus was ranked by the area under the plasma glucose concentration-time curves during OGTT, as follows: rats fed ethanol with low-sucrose diet (EL) > rats fed ethanol with high-sucrose diet (EH) > rats fed control liquid diet (CL) ≒ rats fed solid chow (CS). Despite the marked difference in plasma glucose levels, there was no significant difference in plasma insulin levels during OGTT among the groups. Body weight rank was EH > CL ≒ CS > EL. No differences were observed in plasma triacylglycerol and total cholesterol levels among the four groups throughout the experimental period. These findings suggest that ethanol ingestion combined with lowered sucrose intake aggravates diabetes mellitus in genetically diabetic rats.

Genetic Dissection of “OLETF,” a Rat Model for Non-Insulin-Dependent Diabetes Mellitus: Quantitative Trait Locus Analysis of (OLETF × BN) × OLETF

To identify genetic determinants relevant to non-insulin-dependent diabetes mellitus (NIDDM), we performed a genome-wide analysis for quantitative trait loci (QTLs) using 359 backcross progeny of the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The OLETF strain is a well-studied animal model of obese NIDDM, with features of hyperinsulinemia, hyperglycemia, insulin resistance, and abundant abdominal fat. Our extensive genomic scanning with 218 markers revealed nine significant QTLs, including a strong determinant of obesity on chromosome 1 (Dmo1: LOD = 13.99, for body weight). Two highly significant QTLs for glucose homeostasis were found, one on chromosome 1 (Dmo4 LOD = 7.16, for postprandial glucose level) and the other on chromosome X (Dmo11/Odb1: LOD = 7.81, for postprandial glucose level). These data are comparable to results of our previous studies of the OLETF rat.

Bone loss in a rat model of non-insulin-dependent diabetes mellitus, the OLETF (Otsuka Long-Evans Tokushima fatty strain) rat

A long-term investigation of bone metabolism was conducted in a newly developed strain, the OLETF (Otsuka Long-Evans Tokushima fatty strain) rat, which spontaneously develops non-insulin-dependent diabetes (NIDDM). The OLETF rats used in this study developed hyperglycemia before the age of 24 weeks and overt diabetes before 40 weeks. The bone mineral density (BMD) of the lumbar spine peaked at the age of 24 weeks in the OLETF rats, and declined rapidly after 40 weeks. In addition, the BMD of the tibial proximal metaphysis and diaphysis and the bone strength of the femoral diaphysis peaked at 40 weeks, then declined rapidly. In contrast, the BMD and the bone strength of the LETO (Long-Evans Tokushima Otsuka) rats, used as a control, peaked at 24 weeks, and did not change thereafter. The serum vitamin D metabolites [25-hydroxy vitamin D (25-OHD), 24,25-dihydroxyvitamin D (24,25(OH)2D), and 1,25-dihydroxy vitamin D (1,25(OH)2D)] levels for the OLETF rats declined with age, and were significantly lower than those of the control LETO rats. The level of serum bone-specific alkaline phosphatase (Alp) activity and serum tartrate-resistant acid phosphatase (Tr-Acp) activity in the OLETF rats increased remarkably with age from 24 weeks, and there were significant differences in the 56- and the 69-week values between the OLETF rats and the age-matched control LETO rats. These results suggested that this strain can serve as a useful model for NIDDM with osteopenia.

Evaluation of glomerular lesion and abnormal urinary findings in OLETF rats resulting from a long-term diabetic state

Otsuka Long-Evans Tokushima Fatty (OLETF) rats have been established as an animal model in which non-insulin-dependent diabetes mellitus develops spontaneously. We examined the renal histopathology and the urinary findings serially in OLETF rats and compared these findings with findings in age-matched Long-Evans Tokushima Otsuka (LETO) rats as a control strain. OLETF rats showed higher blood glucose levels than did LETO rats from 18 weeks of age, and hemoglobin A1c levels became higher in OLETF rats than in LETO rats from 22 weeks of age. Accompanying the development of hyperglycemia was an increase in the amount of albuminuria in OLETF rats from 18 weeks of age. The initial histopathologic change found in OLETF rats was an increase in glomerular area, and mesangial expansion started to develop from 22 weeks of age. Mesangial lesions progressed to mesangial sclerosis, and exudative lesions were found in OLETF rats from 36 weeks of age. The anionic charge of glomerular basement membrane (GBM), measured by polyethyleneimine grain density, demonstrated that the lower grain density in OLETF rats when compared with that in LETO rats became more evident with an increase in the amount of albuminuria. Therefore, the defect in the charge-selective property found in OLETF rats might be one of the causes of albuminuria. The GBM became thickened in elderly OLETF rats as compared with that in age-matched LETO rats. Disturbances in the selectivity of urinary protein, as determined by the clearance ratio of immunoglobulin G to transferrin, were found to accompany the thickening of GBM in OLETF rats. We consider that both the loss of the charge-selective property and massive albuminuria might be the causes of GBM thickening, through a clogging mechanism, and that GBM thickening might in turn produce the loss of size selectivity. Given these findings, we consider the OLETF strain of rats to be an interesting animal model for studying the relationship between diabetes and renal involvement, because the glomerular abnormalities and massive albuminuria found in OLETF rats were results of a long-term diabetic state.