Hindawi Publishing Corporation
Journal of Diabetes Research
Volume 2013, Article ID 986462, 9 pages
Phenotypic Characterization of LEA Rat: A New Rat Model of
Nonobese Type 2 Diabetes
Tadashi Okamura,1,2Xiang Yuan Pei,3Ichiro Miyoshi,4,5Yukiko Shimizu,1
Rieko Takanashi-Yanobu,1Yasumasa Mototani,3Takao Kanai,6Jo Satoh,7
Noriko Kimura,8and Noriyuki Kasai3
1Department of Laboratory Animal Medicine, National Center for Global Health and Medicine, Tokyo 162-8655, Japan
2Department of Infectious Diseases, National Center for Global Health and Medicine, Tokyo 162-8655, Japan
3Institute for Animal Experimentation, Tohoku University Graduate School of Medicine, Sendai 980-8575, Japan
4Department of Comparative and Experimental Medicine, Nagoya City University Graduate School of Medical Sciences,
Nagoya 467-8601, Japan
5Center for Experimental Animal Science, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan
6Institute of Laboratory Animals, Tokyo Women’s Medical University, Tokyo 162-8666, Japan
7Division of Diabetes and Metabolism, Department of Internal Medicine, Iwate Medical University School of Medicine,
Morioka 020-8505, Japan
8Pathology Section, Department of Clinical Research, National Hospital Organization Hakodate National Hospital,
Hakodate 041-8512, Japan
Correspondence should be addressed to Noriyuki Kasai; email@example.com
Received 23 November 2012; Accepted 26 December 2012
Academic Editor: Norihide Yokoi
Copyright © 2013 Tadashi Okamura et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
Animal models have provided important information for the genetics and pathophysiology of diabetes. Here we have established
a novel, nonobese rat strain with spontaneous diabetes, Long-Evans Agouti (LEA) rat derived from Long-Evans (LE) strain. The
incidence of diabetes in the males was 10% at 6months of age and 86% at 14months, while none of the females developed diabetes.
The blood glucose level in LEA male rats was between 200 and 300mg/dl at 120min according to OGTT. The glucose intolerance
in correspondence with the impairment of insulin secretion was observed in male rats, which was the main cause of diabetes in
LEA rats. Histological examination revealed that the reduction of 훽-cell mass was caused by progressive fibrosis in pancreatic islets
response to exogenous insulin were comparable to those of control rats. The unique characteristics of LEA rat are a great advantage
not only to analyze the progression of diabetes, but also to disclose the genes involved in type 2 diabetes mellitus.
inage-dependentmanner.Theintracytoplasmichyalinedropletaccumulation andthedisappearance oftubularepithelialcelllayer
associated with thickening of basement membrane were evident in renal proximal tubules. The body mass index and glycaemic
Diabetes mellitus is a heterogeneous group of metabolic
diseases that is characterised by hyperglycaemia. It can result
in blindness, kidney and heart disease, stroke, loss of limbs,
as a primary threat to human health in the 21st century
. Type 2 diabetes mellitus is the most common form of
diabetes and accounts for approximately 90% of cases; its
development is controlled by interactions between multiple
genetic and environmental factors [2–4]. The genetics and
because detailed investigations, such as genetic dissection,
have been restricted in humans for practical and ethical
reasons. Animal models of type 2 diabetes mellitus have pro-
vided important information, and many rat strains of spon-
taneous diabetes have been reported [5–11]. Among these
2 Journal of Diabetes Research
Fatty (OLETF), and Spontaneously Diabetic Torii (SDT) rats
have been widely used for elucidating the genes responsible
for the development of diabetes, the physiological course of
The different diabetes model strains exhibit different aspects
of the disease, and thus additional animal models are needed
to elucidate the complete pathogenesis of diabetes.
We have developed a novel, nonobese rat strain with
spontaneous diabetes, Long-Evans Agouti (LEA) rat, which
was established from a Long-Evans closed colony together
with the Long-Evans Cinnamon (LEC) rat . LEA rats
spontaneously develop hyperglycaemia and glucosuria. They
do not exhibit any signs of obesity throughout their lives but
experience late onset of the disease and exhibit histological
changes (macrophage infiltration and fibrosis) of the pan-
creatic islets. Thus, LEA rats may serve as a new model of
secretion. In the present study, we examined the pathophys-
iological characteristics of the strain and demonstrated that
the LEA rat is a useful model of human nonobese diabetes.
2. Materials and Methods
2.1. Animals. LEA rats, also known as LEA/SENDAI or
SENDAI rats, were maintained at the Institute for Animal
Experimentation, Tohoku University Graduate School of
Medicine, Japan. Wistar rats were purchased from Japan
SLC (Hamamatsu, Japan) and were used as controls. All rats
were housed in air-conditioned animal rooms at an ambient
temperature of 23 ± 3∘C and relative humidity of 50 ± 10%,
Yokohama, Japan), and water were available ad libitum. The
fat content of the diet was 4.1%. All animal care procedures
were approved by the Animal Care and Use Committee
of Tohoku University Graduate School of Medicine, and
complied with the procedures of the Guide for the Care and
Use of Laboratory Animals of Tohoku University.
cycle. Food, consisting of a Labo MR standard diet (Nosan,
2.2. Examination of Clinical Features. Urinary glucose and
AG2 (Eiken, Tokyo, Japan). The detection limits of the Uro-
paper were 10–20mg/dL for urine protein and 40–60mg/dL
for urine glucose. The body weight (BW) and body length
(BL), that is, the distance from the nose to the anus, of five
male rats (6 months old) were measured. The body mass
index (BMI) was calculated as BMI = BW(g)/BL(cm)2.
2.3. Oral Glucose Tolerance Test (OGTT). Glucose tolerance
was estimated by the oral glucose tolerance test (OGTT).
and blood samples were collected from the tail vein at 0, 30,
60, 90, and 120min after loading. The blood glucose levels
were measured with a Glutest EII blood glucose monitoring
meter with a monitoring range of 40–500mg/dL (Sanwa
Kagaku, Nagoya, Japan). The rats were classified according to
the three-grade system of diabetes mellitus (DM), impaired
glucose tolerance (IGT), and normal. DM was defined as
as 120min blood glucose levels between 140 and 199mg/dL.
Neither DM nor IGT was defined as normal.
2.4. Plasma Insulin Concentration and Insulin Tolerance
Test. The plasma insulin concentration was determined as
immunoreactive insulin (IRI) by ELISA with a rat insulin
assay kit (Morinaga Milk Industry, Yokohama, Japan) using
separated plasma from the blood collected from the tail vein
at 0, 30, 60, 90, and 120min after glucose loading. To study
early-phase insulin secretion, an OGTT was performed on
male rats (2 and 12 months of age) as described previously,
and blood glucose levels (BG) and insulin concentrations
(IRI) at 0 and 30min after glucose loading were measured.
The insulinogenic index (ΔI.I.) was calculated as follows:
tolerance test was performed in 12-month-old, nonfasting
a dose of 0.75U/kg BW of human insulin (Novolin R; Novo
Nordisk, Denmark). Blood samples were drawn from the
tail vein at different time points, and glucose levels were
determined as described previously.
ΔI.I. = ΔIRI/ΔBG, where ΔIRI and ΔBG are the differences
between their respective values at 0 and 30min. An insulin
2.5. Histological Analyses. The tissues from rats were fixed
PBS, dehydrated, embedded in paraffin, cut into 5-휇m-
processed for immunostaining by an indirect method using
Guinea pig anti-insulin polyclonal antibody (1:100, DACO,
Carpinteria, CA) as the primary antibody and peroxidase-
International, Temecula, CA) as the secondary antibody. The
specific reactions were visualised with a DAB substrate kit
(Vector, Burlingame, CA). To distinguish the inflammatory
monoclonal antibodies against rat CD4 clone W3/25 (MCA
55R; Abd Serotec, Oxford, UK), CD8 clone OX-8 (MCA48R;
AbD Serotec), CD45RA clone OX-33 (MCA340G, AbD
Serotec), and macrophage antigen clone ED1 (MCA341, AbD
(Nichirei, Tokyo, Japan). Kidney sections were stained with
Guinea pig anti-insulin antibodies (1:100) and analysed
under an Olympus BX51 microscope (Olympus, Tokyo,
Japan) connected to a computer running the WinROOF
overnight at 4∘C in phosphate-buffered saline (PBS) that
contained 4% paraformaldehyde. They were rinsed with
thick sections, and stained with haematoxylin and eosin
(H&E). For insulin detection, the pancreatic sections were
Volume. The volume of 훽-cells relative to the pancreas
method of Bouwens et al. , with some modifications. In
intervals of 100휇m. The sections were immunostained with
volume was calculated as the proportion of the total area of
훽-cells to the total area of pancreatic tissue, according to the
tissue from three animals of each strain were obtained at
Journal of Diabetes Research3
2M6M 12M 14M
Body weight (g)
2468 10 12
Figure 1: (a) Incidence of diabetes mellitus in LEA rats as determined by OGTT. Dotted and closed bars indicate IGT and DM, respectively.
M and F indicate male and female, respectively. 푛 = 32 for males at each age; 푛 = 26 for females at each age. (b) Changes of body weight in
male (open circle, 푛 = 5) and female (open square, 푛 = 5) LEA rats.
software (Mitani Corp., Tokyo, Japan). The image analysis
quantified the total pancreatic tissue area and the insulin-
the relative 훽-cell volume was not attributable to a change in
2.7. Statistical Analyses. The results are expressed as means ±
SD. Differences were analysed using the Student’s t-test. A 푃
positive area was also measured in 20 islets of the five rats of
value < 0.05 was considered statistically significant.
3.1. Incidence of Diabetes. The incidence of diabetes in LEA
mellitus was observed only in male rats, and its incidence
of age, respectively. IGT was observed at 2 months of age in
the rats. The onset of diabetes was not observed in females,
although 33% of the females showed only IGT at 12 months
male rats were used in the experiments. Glucosuria appeared
at 5 months of age, before the onset of diabetes in male rats,
and was present in 100% of the males at 8 months of age.
In female rats, glucosuria appeared at 7 months of age and
was present in 100% of the females at 9 months (Table 1).
Proteinuria appeared at 6 months of age, concomitant with
the onset of diabetes, in male rats and was present in 57% of
the males at 9 months of age, whereas proteinuria appeared
in 20% of female rats at 9 months of age and did not exceed
30% of the females thereafter.
3.2. Body Weight and Survival Rate. The average BWs of
male and female LEA rat increased gradually throughout the
experimental period and were 506 ± 37.8g (푛 = 5) and
312 ± 27.7g (푛 = 5) at the 12 months of age, respectively
(Figure 1(b)). A significant decrease in BW could not be
observed even after the onset of diabetes. The BMI of the
(0.59±0.02g/cm2,푁 = 5),confirmingthattheLEAratswere
plementary Figure 1 available online at http://dx.doi.org/
10.1155/2013/986462). We found that 95% of the male rats
survived to 12 months of age, and 50% survived to 22 months
different from that of normal control Wistar rats, which
indicates that diabetes does not influence the survival of LEA
LEA rats at 6 months of age (0.57 ± 0.02g/cm2, 푁 = 5) was
The survival rate of LEA rats was examined (Sup-
not significantly different from that of the control Wistar rats
3.3. Glucose Tolerance and Insulin Response to Oral Glucose
Loading. The results of the OGTT in male rats at different
ages are shown in Figure 2. Two-month-old male LEA rats
showed impaired glucose tolerance compared with age-
matched male Wistar rats (Figure 2(a)). At 12 and 14 months
of age, the LEA rats presented with typical diabetic glucose
The plasma insulin concentrations in male rats at 2
months of age showed that the pre-OGTT values did not dif-
fer among the rats, whereas the values at 30min after glucose
plasma insulin level was significantly lower in LEA rats at
12 months of age after glucose loading (Figure 2(f)). These
results indicate that LEA rats have impairment of insulin
secretion in response to glucose stimulation. The low insulin
levels measured at 30min after glucose loading suggest that
LEAratshaveadecreasedabilityto secreteinsulinat an early
2(c) and 2(d)). The Wistar rats did not show any change in
blood glucose level in relation to age.
index (ΔI.I.) of male LEA rats was significantly lower at both
2 and 12 months of age compared with that of Wistar rats
4 Journal of Diabetes Research
Time after glucose loading (min)
Blood glucose (mg/dl)
Time after glucose loading (min)
Blood glucose (mg/mL)
0 30 60 90 120
Time after glucose loading (min)
Blood glucose (mg/dl)
Time after glucose loading (min)
Blood glucose (mg/dl)
Time after glucose loading (min)
Plasma insulin (ng/ml)
0 30 60120
Time after glucose loading (min)
Plasma insulin (ng/ml)
Figure 2: Blood glucose levels after glucose loading in male LEA (푛 = 11, open circle) and Wistar rats (푛 = 5, closed circle) at 2 months of
the mean ± SD.∗푃 < 0.05.∗∗푃 < 0.01.
(Table 2), which indicates that early-phase insulin secretion
is significantly impaired at an early age.
the blood glucose levels were significantly higher in LEA rats
than in Wistar rats. After insulin injection, the blood glucose
levels in LEA rats significantly decreased by maximum 51.1%
over 120min to the same levels observed in the Wistar rats.
These results indicate that LEA rats have a normal glycaemic
response to exogenous insulin and are not insulin-resistant.
age (a), in male LEA (푛 = 12, open circle) and male Wistar rats (푛 = 4, closed circle) at 6 months of age (b), in male LEA (푛 = 13, open
circle) and Wistar rats (푛 = 3, closed circle) at 12 months of age (c), in male LEA (푛 = 15, open circle) and Wistar rats (푛 = 3, closed circle)
at 14 months of age (d). Plasma insulin levels after glucose loading in male LEA (푛 = 3, open circle) and Wistar rats (푛 = 4, closed circle) at 2
months of age (e), in male LEA (푛 = 5, open circle) and Wistar rats (푛 = 3, closed circle) at 12 months of age (f). Each value is expressed as
3.4. Pathological Changes of Pancreatic Islets in Male LEA
Rat. The age-dependent histological changes in the pancreas
were examined (Figure 4). Male LEA rats at 2 months of
age had inflammatory reaction in fraction of the pancreatic
islets (Figure 4(a)), although the most of islets were intact.
Immunostaining for insulin revealed that insulin-positive
cells were irregularly distributed within inflammatory foci
(Figure 4(b)). The inflamed islets were infiltrated by cells
positive for anti-rat macrophage antibody (Figure 4(c)) but
not for antibodies against CD4+, CD8+, or CD45RA (data
this age. The number and size of islets decreased significantly
with age. However, inflammatory reactions disappeared by
6 months of age, and the islets had been replaced by
fibrotic remnants in rats over 12 months of age (Figure 4(d)).
The number of 훽-cells was reduced, although 훽-cells were
Journal of Diabetes Research5
Table 1: Incidence of glucosuria and proteinuria in LEA rats (%).
79 1011 12
푛 = 32 for males; 푛 = 35 for females.
male LEA rat.
0.103 ± 0.07∗
0.153 ± 0.04∗
0.608 ± 0.1910.583± 0.269
∗푃 < 0.05 compared to age matched Wistar rat.
0 15 30 6090120
Blood glucose (mg/dl)
after abdominal administration of insulin (0.75IU/Kg) to nonfast-
circle)at12monthsofage. Significantreduction(푃 < 0.01)inblood
ing male LEA (푛 = 4, open circle) and Wistar rats (푛 = 4, closed
glucose levels of LEA and Wistar rats was shown with measuring
SD.∗푃 < 0.05.∗∗푃 < 0.01.
times after insulin injection. Each value is expressed as the mean ±
present at 12 months of age (Figure 4(e)). A few tiny islets
without fibrosis, which appeared to be regenerative islets,
were intermingled in the affected pancreas in rats from 12
months of age (Figures 4(f) and 4(g)). The pancreatic islets
fibrosis and inflammatory reaction.
The volume of 훽-cells relative to the gross volume of
albeit not statistically significant, trend from 0.79 ± 0.05% at
age appears in LEA rats owing to severe fibrosis of the islets.
the pancreas was determined using the WinROOF software
to analyse sections that were immunostained for insulin
(Figure 4(h)). In male LEA rats, the volume of 훽-cells signifi-
To identify whether the diminished 훽-cell mass in LEA
at 6 months. The control Wistar rat strain showed a rising,
2 months to 0.96 ± 0.24% at 6 months. These results reveal
that the significant decrease in the insulin-positive area with
rats was caused by a reduction in cell number or atrophy of
the cells, we counted the number of nuclei in the insulin-
positive areas of 20 islets in five of each of 6-month-old
LEA and Wistar rats. The number of nuclei did not differ
versus 128.82 ± 13.35휇m2/nuclei for LEA versus Wistar
rats, resp.). These results indicate that a reduction in the
cell number (not atrophy of 훽-cells) is responsible for the
LEA rats, glucosuria and proteinuria were present in 100% at
8 months of age and in 66% of males at 12 months of age,
respectively. The histopathological analysis was performed
to examine the renal lesions in 12-month-old male LEA rats
(Figure 5). The large dilatation of tubular lumen was present,
mostly in superficial cortex regions (Figure 5(a)). Atrophy
of tubular epithelium and flattend/detached renal tubules
were also observed (Figure 5(b)). The intracytoplasmic hya-
line droplet accumulation and the disappearance of tubular
epithelial cell layer associated with thickening of basement
membrane were evident in proximal tubules (Figure 5(c)).
There were no obvious pathological changes in the glomeruli
at 12 months of age (Figure 5(d)).
reduction of 훽-cell volume in LEA rats.
Two inbred strains, Long-Evans Agouti (LEA) and Long-
Evans Cinnamon (LEC), which were selected for coat color,
were established from a closed colony of Long-Evans rats at
the Center for Experimental Plants and Animals, Hokkaido
University (Japan) . The LEA rat has been known as the
control strain for the LEC rat, an animal model of Wilson
disease . However, the large amount of urine and the
observed in LEA rats during long-term breeding. In 1996, we
found three male rats that were positive for glucosuria and
hyperglycaemia among littermates from an inbred colony of
LEA/Hkm. The LEA rats exhibit several distinctive diabetes-
phase insulin secretion is impaired at 2 months of age; (3)
the progressive fibrosis in islet in an age-dependent manner;
(4) a normal glycaemic response to exogenous insulin; (5)
a new rat model for nonobese type 2 diabetes mellitus.
Several rat model strains of spontaneous type 2 dia-
betes mellitus have been identified to date, and they are
6 Journal of Diabetes Research
Beta cell area/pancreas
antibody (b), and staining with anti-ED1 antibody (c). At 12 months of age, H&E staining (d and f) and staining with anti-insulin antibody
LEA and Wistar rats, respectively, at 2 months and 6 months of age. Each value is expressed as the mean ± SD.∗푃 < 0.05.∗∗푃 < 0.01.
classified into two types, obesity and nonobesity models.
The obesity models of type 2 diabetes, such as Sand ,
Wistar fatty , and OLETF rats , are characterised by
hyperglycaemia, hyperinsulinemia, and insulin resistance. In
contrast, the nonobesity models, such as GK , WBN/Kob
, and Spontaneously Diabetic Torii (SDT) rats [11, 19],
are characterised by hyperglycaemia, hypoinsulinemia, and
model because BMI of LEA rats is not different from that of
control rats. However, there are several differences between
the GK and LEA rats. In GK rats, there is no sex difference
with respect to the occurrence of diabetes and no age-
dependent deterioration of impaired glucose tolerance; in
SDT rat is a new model of nonobese, severe type 2 diabetes
mellitus with hyperglycaemia, hemorrhage in and around
(e and g). Sections (b), (e), and (g) correspond to sections of (a), (b), and (f). Scale bar = 100휇m. (h) Changes in the proportions of 훽-cells in
the pancreas with age. The areas of the 훽-cells and pancreas were calculated by computer-aided imaging. Open and closed bars indicate male
the islets, and hyposecretion of insulin (hypoinsulinemia)
resulting from a significantly decreased number and size of
islets . Although LEA rats displayed no hemorrhage in
and around the islets, macrophage infiltration was present
around the islets, leading to the progressive fibrosis of islet
The glucose intolerance in correspondence with the
impairment of the insulin secretion was observed in male
LEA (Figure 2 and Table 2), suggesting that the main cause
of diabetes in LEA rats is hypoinsulinemia attributable to
phase insulin secretion is caused by the hypofunction of 훽-
a decreased number of 훽-cells in the islets (Figure 4). It
cells. Although there was inflammatory reaction in fraction
of the pancreatic islet in male LEA rats at 2 months of
is also likely that significant decreased capability of early-
age, the volume of 훽-cells in LEA rats was comparable to
Journal of Diabetes Research7
Figure 5: Histopathological appearance of renal tissues from male LEA rats at 12 months of age. Stained with Masson’s Trichrome (a–d).
Epithelial layer effacement (asterisk), Glomeruli (arrow). Scale bars = 200휇m (a), 100휇m (b and d) and 50휇m (c).
that of control rats (Figure 4(h)), suggesting that LEA rats
have congenital defect of insulin secretion in addition to
reflects the first phase of insulin secretion from pancreatic 훽-
to suppress the increasing blood glucose concentration that
occurs after feeding because of a decreased ability to secrete
insulin in the early phase, which eventually leads to the
in the number of 훽-cells is thought to be the main cause
rat models of type 2 diabetes mellitus [22–26].
Both congenital and acquired factors are involved in
the progressive reduction of 훽-cell mass in age-dependent
the liver . Therefore, we suggest that the LEA rat is unable
manner. The ability to secrete insulin in the early phase
of type 2 diabetes in LEA rats, and this is supported by
previous observations in human type 2 diabetes patients and
the mechanism of 훽-cell reduction. In regard to congenital
Butler et al.  have revealed that apoptosis reduces 훽-
factors, mutations in transcription factor genes, such as
factor-1훼 (HNF-1훼) , have been verified. Hyperglycaemia
cells in human diabetes and that it progresses by amyloid
deposition and hyperglycaemia. Zhu et al.  have reported
and hyperlipidaemia have been reported as acquired factors.
that the impairment of 훽-cell proliferation causes a decrease
in 훽-cells under hyperglycaemic conditions in OLETF rats,
and Movassat et al.  have observed that glucose toxi-
city leads to a reduction in 훽-cells in GK rats. Free-fatty-
Diabetic Fatty (ZDF) rats. Although it is speculated that the
by macrophages cause the reduction in 훽-cells in LEA rats,
The systemic complications associated with diabetes are
major causes of morbidity and mortality. The abnormality of
rats with glycosuria and proteinuria (Figure 5 and Table 1).
Onset of diabetes as determined by OGTT was observed in
only male LEA rats (Figure 1(a)), and its incidence increased
However, glucosuria appeared at 5 months of age before the
onset of diabetes in male rats, and was present in 100% of the
(Figure 1(a)). Based on these findings, it is unlikely that the
onset of diabetes and impairment of glucose intolerance are
not associated with glucosuria and proteinuria. Although the
LEA rat is used as the control strain of the LEC rat since they
do not harbor Atp7b mutation , the several phenotypes
such as hypersensitivity to X-rays  and the lack of D-
amino acid oxidase (DAO) activity , which is involved in
acid- (FFA-) induced 훽-cell apoptosis has been proposed by
Shimabukuro et al.  as the underlying cause in Zucker
impairment of 훽-cell proliferation, progression of apoptosis
further analyses are required to clarify the pathogenesis of
diabetes in LEA rats.
by hyperglycaemia, and impairment by cytokines produced
8 Journal of Diabetes Research
the degradation of D-serine, a key coagonist for N-methyl-
d-aspartate (NMDA) receptor, have been reported. We are
now performing quantitative trait locus (QTL) analyses for
impaired glucose tolerance and urinary glucose to lead us to
identification of genes for glucose intolerance, renal glucose
excretion, and the development of diabetes in LEA rat.
In conclusion, the LEA rat has distinctive characteristics
that are different from the previously described model rats.
The LEA rats develop late onset diabetes in correspondence
with the impairmentof the insulin secretion, which is caused
by progressive fibrosis in pancreatic islets in age-dependent
manner. In Japan, the prevalence of type 2 diabetes mellitus
is increasing rapidly, and more than 10% of individuals over
in Japan are obese, and impairment of insulin secretion
often develops before onset of diabetes . The unique
characteristics of LEA rat are a great advantage to analyze
the progression of diabetes mellitus with age. The additional
studies are expected to disclose the genes involved in type 2
The authors thank Ms. Chieko Suto for technical assistance.
This work was supported by Grant-in-Aid for Scientific
Research of Japan Society from the Promotion of Science
(to N. Kasai and T. Okamura), and from Ministry of Health,
Labour and Welfare (to T. Okamura).
implications of the diabetes epidemic,” Nature, vol. 414, no.
6865, pp. 782–787, 2001.
 K. G. Alberti and P. Z. Zimmet, “Definition, diagnosis and
classification of diabetes mellitus and its complications. Part
1: diagnosis and classification of diabetes mellitus provisional
reportofaWHOconsultation,” Diabetic Medicine,vol.15,no.7,
pp. 539–553, 1998.
 H. King, R. E. Aubert, and W. H. Herman, “Global burden
of diabetes, 1995–2025: prevalence, numerical estimates, and
projections,” Diabetes Care, vol. 21, no. 9, pp. 1414–1431, 1998.
 P. Zimmet, “Globalization, coca-colonization and the chronic
disease epidemic: can the doomsday scenario be averted?”
Journal of Internal Medicine, vol. 247, no. 3, pp. 301–310, 2000.
Horton, and T. D. Kinney, “The sand rat (psammomys obesus)
as an experimental animal in studies of diabetes mellitus,”
Diabetologia, vol. 3, no. 2, pp. 130–134, 1967.
 H. Ikeda, A. Shino, T. Matsuo, H. Iwatsuka, and Z. Suzuoki,
“A new genetically obese-hyperglycemic rat (Wistar fatty),”
Diabetes, vol. 30, no. 12, pp. 1045–1050, 1981.
 K. Kawano, T. Hirashima, S. Mori, Y. Saitoh, M. Kurosumi,
and T. Natori, “Spontaneous long-term hyperglycemic rat with
diabetic complications: Otsuka Long-Evans Tokushima Fatty
(OLETF) strain,” Diabetes, vol. 41, no. 11, pp. 1422–1428, 1992.
 Y. Goto, M. Kakizaki, and N. Masaki, “Spontaneous diabetes
produced by selective breeding of normal Wistar rats,” Proceed-
ings of the Japan Academy, vol. 51, pp. 80–85, 1975.
 K. Nakama, K. Shichinohe, K. Kobayashi et al., “Spontaneous
diabetes-like syndrome in WBN/Kob rats,” Acta Diabetologica
Latina, vol. 22, no. 4, pp. 335–342, 1985.
 M. Shinohara, T. Masuyama, T. Shoda et al., “A new sponta-
neously diabetic non-obese torii rat strain with severe ocular
complications,” International Journal of Experimental Diabetes
Research, vol. 1, no. 2, pp. 89–100, 2000.
 D. Gauguier, P. Froguel, V. Parent et al., “Chromosomal map-
ping of genetic loci associated with non-insulin dependent
diabetes in the GK rat,” Nature Genetics, vol. 12, no. 1, pp. 38–
 S. Wei, K. Wei, D. H. Moralejo et al., “Mapping and charac-
terization of quantitative trait loci for non-insulin- dependent
diabetes mellitus with an improved genetic map in the Otsuka
no. 3, pp. 249–258, 1999.
 T. Masuyama, M. Fuse, N. Yokoi et al., “Genetic analysis for
diabetes in a new rat model of nonobese type 2 diabetes,
Spontaneously Diabetic Torii rat,” Biochemical and Biophysical
Research Communications, vol. 304, no. 1, pp. 196–206, 2003.
 M. Sasaki, M. C. Yoshida, and K. Kagami, “Spontaneous
hepatitis in an inbred strain of Long-Evans rats,” Rat News
Letter, vol. 14, pp. 4–6, 1985.
 L. Bouwens, R. N. Wang, E. de Blay, D. G. Pipeleers, and G.
Kloppel, “Cytokeratins as markers of ductal cell differentiation
and islet neogenesis in the neonatal rat pancreas,” Diabetes, vol.
43, no. 11, pp. 1279–1283, 1994.
 N. Kasai, T. Osanai, I. Miyoshi, E. Kamimura, M. C. Yoshida,
and K. Dempo, “Clinico-pathological studies of LEC rats
with hereditary hepatitis and hepatoma in the acute phase of
hepatitis,” Laboratory Animal Science, vol. 40, no. 5, pp. 502–
 Y. Li, Y. Togashi, S. Sato et al., “Spontaneous hepatic copper
accumulation in Long-Evans cinnamon rats with hereditary
hepatitis: a model of Wilson’s disease,” Journal of Clinical
Investigation, vol. 87, no. 5, pp. 1858–1861, 1991.
 T. Masuyama, K. Komeda, A. Hara et al., “Chronological char-
acterization of diabetes development in male Spontaneously
Diabetic Torii rats,” Biochemical and Biophysical Research Com-
munications, vol. 314, no. 3, pp. 870–877, 2004.
 S. Yagihashi, Y. Goto, M. Kakizaki, and N. Kaseda, “Thickening
of glomerular basement membrane in spontaneously diabetic
rats,” Diabetologia, vol. 15, no. 4, pp. 309–312, 1978.
 G. Williams and J. C. Pickup, Handbook of Diabetes, Blackwell
Science, Oxford, UK, 3rd edition, 2004.
 K. Saito, N. Yaginuma, and T. Takahashi, “Differential volume-
try of A, B and D cells in the pancreatic islets of diabetic and
vol. 129, no. 3, pp. 273–283, 1979.
 J. Movassat, C. Saulnier, and B. Portha, “훽-cell mass depletion
Metabolisme, vol. 21, no. 5, pp. 365–370, 1995.
 A. Pick, J. Clark, C. Kubstrup et al., “Role of apoptosis in failure
precedes the onset of hyperglycaemia in the GK rat, a genetic
model of non-insulin-dependent diabetes mellitus,” Diabete et
of 훽-cell mass compensation for insulin resistance and 훽-cell
Journal of Diabetes Research9 Download full-text
defects in the male Zucker diabetic fatty rat,” Diabetes, vol. 47,
no. 3, pp. 358–364, 1998.
 M. Zhu, Y. Noma, A. Mizuno, T. Sano, and K. Shima, “Poor
capacity for proliferation of pancreatic 훽-cells in Otsuka-Long-
 A. E. Butler, J. Janson, S. Bonner-Weir, R. Ritzel, R. A. Rizza,
Evan-Tokushima fatty rat: a model of spontaneous NIDDM,”
Diabetes, vol. 45, no. 7, pp. 941–946, 1996.
andP.C.Butler,“훽-celldeficit andincreased 훽-cellapoptosis in
secretion and increased insulin sensitivity in familial maturity-
onset diabetes of the young 4 (insulin promoter factor 1 gene),”
Diabetes, vol. 49, no. 11, pp. 1856–1864, 2000.
humans with type 2 diabetes,” Diabetes, vol. 52, no. 1, pp. 102–
tion in hepatocyte nuclear factor 1훼-deficient mice,” Journal of
 J. Movassat, C. Saulnier, P. Serradas, and B. Portha, “Impaired
development of pancreatic beta-cell mass is a primary event
during the progression to diabetes in the GK rat,” Diabetologia,
vol. 40, no. 8, pp. 916–925, 1997.
 M. Shimabukuro, Y. T. Zhou, M. Levi, and R. H. Unger, “Fatty
Clinical Investigation, vol. 101, no. 10, pp. 2215–2222, 1998.
acid-induced 훽 cell apoptosis: a link between obesity and
a deletion in the copper transporting ATPase gene homologous
to the Wilson disease gene,” Nature Genetics, vol. 7, no. 4, pp.
 K. Masuda, T. Miyamoto, A. R. Cho, and T. Agui, “Analysis of
the cell cycle of fibroblasts derived from the LEC rat after X-
irradiation,” Japanese Journal of Veterinary Research,vol.53,no.
3-4, pp. 141–148, 2006.
 R. Konno, T. Okamura, N. Kasai, K. H. Summer, and A. Niwa,
vol. 37, no. 2, pp. 367–375, 2009.
 M. Fukushima, H. Suzuki, and Y. Seino, “Insulin secretion
capacity in the development from normal glucose tolerance to
supplement 1, pp. S37–S43, 2004.
diabetes,” Proceedings of the National Academy of Sciences of the
United States of America, vol. 95, no. 5, pp. 2498–2502, 1998.