ILAR Journal Online, Volume 32(3) 1990: New Rat Models of Obesity and Type II Diabetes

Online Issues

<< All Back-issues

<< This Issue's Table of Contents

ILAR Journal V32(3) 1990
New Rat Models of Obesity and Type II Diabetes

Wistar Diabetic Fatty Rat
Ruth Kava, Richard G. Peterson, David B. West, and M. R. C. Greenwood

Ruth Kava is assistant director, Obesity Research Center Animal Model Laboratory, Department of Biology, Vassar College, Poughkeepsie, New York. Richard G. Peterson is professor, Department of Anatomy, Indiana University School of Medicine, Indianapolis. David B. West is assistant professor, Department of Physiology, Eastern Virginia Medical School, Norfolk. M. R. C. Greenwood is professor, Department of Nutrition, University of California, Davis.

Development of the Model

Wistar diabetic fatty (WDF/Ta-fa) rats were developed by Ikeda et al. (1981) to provide a rat model of non-insulin-dependent diabetes mellitus (NIDDM). Human NIDDM is typically characterized by adult onset and varying degrees of obesity, hyperglycemia, hyperinsulinemia, insulin resistance, glucose intolerance, and peripheral neuropathy. To produce a model demonstrating such characteristics, these investigators crossed the genetically obese Zucker (fa/fa) rat with the somewhat carbohydrate-intolerant lean Wistar Kyoto rat. H. Ikeda and T. Matsuo of the Takeda Chemical Industries have kindly provided the following detailed history of the resulting WDF/Ta-fa strain:

1971: Wistar Kyoto rats were brought to Takeda Chemical Industries.
1972: Inbreeding of Wistar Kyoto rats was started at Takeda.
1975:F8 Wistar Kyoto and lean heterozygote (+/ fa) Zucker rats (M13 stock; Zucker and Zucker, 1961) were bred to produce the new Wistar diabetic fatty strain (WDF/Ta-fa). Backcrossing was started with these hybrids and the Wistar Kyoto F8 rats to preserve the fa gene and eliminate other alleles of the Zucker background strain.
1975-1979: Backcrossing of the Wistar diabetic fatty rat with the Wistar Kyoto rats and inbreeding of the Wistar Kyoto rats continued; current generation inbred Wistar Kyoto rats were used in each backcross until F22 Wistar Kyoto rats were used in the N11 backcross.
1979-present: Inbreeding of the Wistar diabetic fatty strain began using N11 backcrossed stock. The data reported in the paper by Ikeda et al. (1981) were from the F1 generation of WDF/Ta-fa inbreeding.

Obese male rats of the new WDF/Ta-fa strain were hyperglycemic, hyperinsulinemic, and glucose intolerant and had decreased whole-body insulin sensitivity (Ikeda et al., 1981). They also exhibited hepatic insulin resistance (Sugiyama et al., 1989a) and abnormal pancreatic responses to arginine infusion (Seino et al., 1984) when compared to lean controls.

Expression of NIDDM in this model was sexually dimorphic, with only the obese WDF/Ta-fa males exhibiting the diabetic syndrome (Ikeda et al., 1981). However, when obese WDF/Ta-fa females were fed either a high-sucrose diet (Matsuo et al., 1984a) or given a 30 percent sucrose solution (Sugiyama et al., 1989b), they also developed the hyperglycemia, hyperinsulinemia, and decreased insulin sensitivity exhibited by obese male WDF/Ta-fa rats fed laboratory chow.

Although both WDF/Ta-fa and Zucker rats share the fa gene for obesity, their metabolic profiles differ in several respects. Obese male WDF/Ta-fa rats are more hyperglycemic, glucose intolerant, and insulin resistant, but they are less hyperlipidemic than obese male Zucker rats (Matsuo et al., 1984b).

In 1984, 1985, and 1986, breeding pairs of the new WDF/Ta-fa strain were sent to the Obesity Research Center's Animal Model Core at Vassar College, Poughkeepsie, New York (ORC colony) and to the Diabetes Research Training Center at the Indiana School of Medicine, Indianapolis (DRTC colony). The backgrounds of each of these distributions from Japan are as follows:

1984: to the DRTC Animal Core (N11, F8)
1985: to the ORC Animal Core (N11, F8)
1986: to the DRTC Animal Core (N11, F11)

Because the animals supplied to these sites were at different stages of inbreeding, they cannot be presumed to be genetically identical. Therefore, in this review, we separately describe the maintenance and characteristics of rats from each colony and compare them to those from the parent colony and to other genetically obese rodent models.

DRTC Core Colony

The group of rats received in 1984 by the DRTC Animal Core was crossed with WKY/N stock. This closed breeding colony was subsequently maintained in contact with animals that were infected with mycoplasma and pinworms, and the colony had to be destroyed. The obese male rats from these WDF/Ta-fa x WKY/N crosses exhibited neuropathic complications similar to those seen in other animal diabetes models and in human diabetes. Motor nerve conduction velocity was significantly reduced in obese diabetic rats compared to lean control rats (Peterson et al., 1988b). As do other rodent diabetic models, these obese male rats also exhibited abnormalities in sciatic nerve carbohydrate content, phospholipid metabolism, and protein phosphorylation (Berti-Mattera et al., 1989).

The rats received in 1986 by the DRTC Animal Core have been maintained in microisolators and monitored regularly for disease. Inbreeding has continued. These rats are currently at generation Fl8 of inbreeding. Standard nomenclature for this inbred substrain of WDF/Ta-fa rats is WDF/TaDrt-fa (D. Greenhouse, Institute of Laboratory Animal Resources [ILAR], National Research Council, personal communication, 1989).

Obese male WDF/TaDrt-fa rats appear to be consistently diabetic (Peterson et al., 1988a), as was originally reported in WDF/Ta-fa rats by Ikeda et al. (1981). They are heavier than their lean littermates by seven weeks of age, a factor that increases with age (Figure 1A). Similarly, they are significantly hyperglycemic when compared to lean controls (Figure 1B). The lean rats show no changes in fed (nonfasted) blood glucose levels over time, while those of the obese rats increase between 7 and 10 weeks, plateauing at about 350-400 mg percent.

ORC Core Colony

The WDF/Ta-fa rats received by the ORC Animal Model Laboratory at Vassar College in 1985 have been maintained by outbreeding in a closed, conventionally housed colony. Specifically, mated rats have no parents or grandparents in common. Standard nomenclature for this outbred WDF/Ta-fa subline is Vc:WDF/Ta-fa (D. Greenhouse, ILAR, personal communication, 1989).

Male offspring of the animals received from Japan were monitored for obesity and levels of fed plasma glucose. As shown in Figure 2A, obese males were consistently heavier than their lean littermates. These rats did not exhibit overt hyperglycemia until fed a high-sucrose diet (68 percent of calories from sucrose) at 21 weeks of age (Figure 2B), at which time the plasma glucose of obese, but not of lean, males increased significantly. Thus, the obese male Vc:WDF/Ta-fa rats exhibited a diet-sensitive hyperglycemia.

Further research on these animals has focused on the sexual dimorphism of diabetes expression in the obese rats and its modification by dietary sucrose. Unlike animals from the original Japanese colony, obese female Vc:WDF/Ta-fa rats did not develop overt hyperglycemia, even when fed a high-sucrose diet from 5 to 22 weeks of age (Kava et al., 1987, 1989). Both obese males and females were, however, significantly hyperinsulinemic compared to lean rats fed the same diet. The plasma insulin response to an intragastric glucose load was attenuated in obese males compared to obese female rats, while the plasma glucose response of the males exceeded that of the females (Kava et al., 1989). In older rats (6 to 8 months of age), obese males are significantly more hyperglycemic than obese females, even when fed chow (Figure 3).

The sexual dimorphism in diet sensitivity was confirmed in older animals fed the same high-sucrose diet for two weeks (Figure 3). Interestingly, when sucrose was added to the rats' diet as a liquid supplement (20 percent sucrose, w/v), obese female Vc:WDF/Ta-fa rats had hyperglycemic and hyperinsulinemic responses similar to those of the obese males (Figures 4A and 4B). Thus, the extent of the diabetic pathology exhibited in these animals seems to be affected by the form of dietary sucrose as well as by diet composition.

Sexual dimorphism of NIDDM in Vc:WDF/Ta-fa rats is not extinguished by neonatal castration, nor does ovariectomy at 3 days of age exacerbate glucose intolerance in obese females (Greenwood et al., 1988; Lukasik et al., 1987). Similarly, early castration did not improve the glucose homeostasis of obese male Vc:WDF/Ta-fa rats, but did significantly improve insulin sensitivity of obese male Zucker rats (Kava et al., 1990).

Adrenalectomy had a greater impact on glucose homeostasis in obese male Zucker rats than it did in obese male Vc:WDF/Ta-fa rats (Kava et al., in press).

Obese Zucker rats have elevated hepatic glucose production (HGP) and hepatic and peripheral insulin resistance compared to lean controls (Terrettaz and Jeanrenaud, 1983). Obese female Vc:WDF/Ta-fa rats, when given a 20 percent sucrose supplement, also exhibit extreme hepatic insulin resistance as measured by the euglycemic clamp technique. Unlike the obese Zucker rats studied by Terrettaz and Jeanrenaud (1983), the obese Vc:WDF/Ta-fa animals also have significantly elevated basal HGP compared to lean controls (West et al., in press). This excessive HGP by Vc:WDF/Ta-fa rats is linked, as in the WDF/Ta-fa animals (Matsuo et al., 1984b; Sugiyama et al., 1989a) to abnormalities of hepatic gluconeogenic enzymes. I. J. Turkenkopf and colleagues (Vassar College, Poughkeepsie, N.Y., unpublished data) found 30 percent more phosphoenolpyruvate-carboxy kinase (PEP-CK) mRNA in livers of obese male Vc:WDF/Ta-fa rats than in livers of lean controls.

Discussion

Human NIDDM is a heterogeneous disorder with unclear pathogenesis (Sussman, 1985). The degree of obesity, glucose intolerance, insulin response to glucose, target tissue insulin sensitivity, and susceptibility to vascular disease may vary (Fajans, 1984). Susceptibility to NIDDM is greater in obese men than equally obese women (Krotkiewski et al., 1983). In the related genetically obese animal models described in this review, we may well have a reflection of the diversity of the human condition. For example, obese males of the WDF/Ta-fa and WDF/ TaDrt-fa strains exhibit high levels of nonfasted hyperglycemia by 8 to 10 weeks of age, while those of the Vc:WDF/Ta-fa subline do so at a much older age or when challenged with a high-sucrose diet. In this respect, this subline is similar to the SHR/N-cp rat, which is also sucrose sensitive (Michaelis et al., 1984). Both WDF/Ta-fa and Vc:WDF/Ta-fa rats exhibit sexual dimorphism in the expression of the diabetic syndrome; however, the sex difference seems more robust in the latter group of animals. The existence and stability of sex differences in the WDF/TaDrt-fa substrain have not yet been investigated.

Subtle differences in genetic background may well account for these variations in susceptibility to gender-and diet-linked hyperglycemia. In the genetically obese db/db mouse, for example, susceptibility to hyperglycemia and its modulation by sex steroids are profoundly affected by the genetic background on which the mutant gene is placed (Coleman, 1982; Leiter et al., 1987, 1989). Interestingly, glucose intolerance seems to be ameliorated by the removal of steroid hormones to a greater extent in the related Zucker rat than in the obese Vc:WDF/Ta-fa rat (Kava et al., in press).

In summary then, the relatively new WDF/Ta-fa, Vc:WDF/ Ta-fa, and WDF/TaDrt-fa rats have a number of characteristics that should make them extremely useful models of human NIDDM. To the extent that they have been characterized, these animals exhibit, to varying degrees:

hyperglycemia and hyperinsulinemia;
peripheral and hepatic insulin resistance linked to abnormalities in enzyme levels and activities;
diet- and sex-susceptible diabetes; and
possible diabetes-linked peripheral neuropathy.

Investigators should be careful to select the best substrain for any particular investigation. With that caveat in mind, however, the Wistar diabetic fatty rat should prove an extremely useful tool in increasing our understanding of the etiology and pathologies of human NIDDM.

Address correspondence to Ruth Kava, Assistant Director, ORC Animal Model Lab, Biology Department, Vassar College, Poughkeepsie, NY 12601 (914/437-7310).

References

Berti-Mattera, L. M., J. Lowery, R. G. Peterson, and J. Eichberg. 1989. Alteration of phosphoinositide metabolism, protein phosphorylation and carbohydrate levels in sciatic nerve from Wistar fatty diabetic rats. Diabetes 38:373-378.

Coleman, D. L. 1982. Diabetes-obesity syndromes in mice. Diabetes 3 l(suppl. 1):1-6.

Fajans, S. S. 1984. Heterogeneity within type II and MODY diabetes. Pp. 65-87 in Comparison of Type I and Type II Diabetes. Advances in Experimental Medicine and Biology, vol. 189, M. Vranic, C. H. Hollenberg, and G. Steiner, eds. New York: Plenum.

Greenwood, M. R. C., R. Kava, D. B. West, and V. A. Lukasik. 1988. Wistar fatty rat: A sexually dimorphic model of human noninsulin-dependent diabetes. Pp. 316-319 in Frontiers in Diabetes Research. Lessons from Animal Diabetes II, E. Shafrir and A. E. RenoId, eds. London: John Libbey.

Ikeda, H., A. Shino, and T. Matsuo. 1981. A new genetically obese-hyperglycemic rat (Wistar fatty). Diabetes 30:1045-1050.

Kava, R., D. B. West, V. A. Lukasik, and M. R. C. Greenwood. 1987. Adipose tissue distribution and the sexual dimorphism of NIDDM in the Wistar fatty rat. Fed. Proc. 46(3):881.

Kava, R., D. B. West, V. A. Lukasik, and M. R. C. Greenwood. 1989. Sexual dimorphism of hyperglycemia and glucose tolerance in the Wistar fatty rat. Diabetes 38:159-163.

Kava, R., D. B. West, C. Wypijewski, Z. Wojnar, and M. R. C. Greenwood. 1990. Neonatal castration improves insulin sensitivity more in obese Zucker than in obese Wistar diabetic fatty rats. FASEB J. 4(4):A918.

Kava, R., C. Horowitz, Z. Wojnar, I. Turkenkopf, P. R. Johnson, and M.R. C. Greenwood. In press. Adrenalectomy alters glucose homeostasis in a strain-dependent manner in Zucker and Wistar fatty rats. Int. J. Obesity (abstr.).

Krotkiewski, M., P. Bjorntorp, L. Sjostrom, and U. Smith. 1983. Impact of obesity on metabolism in men and women. J. Clin. Invest. 72:1150-1162.

Leiter, E. H., P. H. Le, and D. L. Coleman. 1987. Susceptibility to db gene and streptozotocin-induced diabetes in C57BL mice: Control by gender-associated, MHC-unlinked traits. Immunogenetics 26:6-13.

Leiter, E. H., H. D. Chapman, and D. L. Coleman. 1989. The influence of genetic background on the expression of mutations at the diabetes locus in the mouse. V. Interactions between the db gene and hepatic sex steroid sulfotransferases correlates with gender-dependent susceptibility to hyperglycemia. Endocrinology 124:912-922.

Lukasik, V. A., R. Kava, D. B. West, and M. R. C. Greenwood. 1987. Early effects of obesity and neonatal ovariectomy on growth and glycemia in the Wistar Kyoto fatty rat. Fed. Proc. 46(3):881.

Matsuo, T., H. Ikeda, H. Iwatsuka, and Z. Suzuoki. 1984a. Role of sucrose diet in the development of hyperglycemia in female Wistar fatty rats. Pp. 261-263 in Lessons from Animal Diabetes, E. Shafrir and A. E. Renold, eds. London: John Libbey.

Matsuo, T., Y. Sugiyama, H. Ikeda, T. Fujita, H. Iwatsuka, and Z. Suzuoki. 1984b. Predisposition to hyperglycemia and hypertriglyceridemia in two genetically obese rats Wistar and Zucker fatty rats. Pp. 257-260 in Lessons from Animal Diabetes, E. Shafrir and A. E. Renold, eds. London: John Libbey.

Michaelis IV, O. E., K. C. Ellwood, J. M. Judge, N. W. Schoene, and C. T. Hansen. 1984. Effect of dietary sucrose on the SHR/N-corpulent rat: A new model for insulin-independent diabetes. Am. J. Clin. Nutr. 39:612-618.

Peterson, R. G., M.-A. Neel, and L. A. Little. 1988a. Comparison of metabolic data from the WKY/N and Wistar fatty (WDF) rat. Pp. 113-119 in New Models of Genetically Obese Rats for Studies in Diabetes, Heart Disease, and Complications of Obesity, C. T. Hansen and O. E. Michaelis IV, eds. Bethesda, Md.: National Institutes of Health.

Peterson, R. G., A. K. Sharma, L. A. Little, M. Neel, C. G. Potter, and J. Eichberg. 1988b. Peripheral nerve abnormalities in Wistar fatty diabetic rats. Pp. 488-491 in Frontiers in Diabetes Research. Lessons from Animal Diabetes II, E. Shafrir and A. E. Renold, eds. London: John Libbey.

Seino, Y., S. Seino, M. Usami, K. Tsuda, J. Takemura, S. Nishi, H. Ishida, and H. Imura. 1984. Somatostatin, glucagon, and insulin secretion from isolated perfused pancreas of new genetically obese hyperglycemic rats. Metabolism 33(5):429-431.

Sugiyama, Y., Y. Shimura, and H. Ikeda. 1989a. Pathogenesis of hyperglycemia in genetically obese-hyperglycemic rats, Wistar fatty: Presence of hepatic insulin resistance. Endocrinol. Japon. 36(1):65-73.

Sugiyama, Y., Y. Shimura, and H. Ikeda. 1989b. Derangement in hepatic enzymes caused by sucrose-drinking and its implication for the development of hyperglycemia in female Wistar fatty rats. Endocrinol. Japon. 36(2):245-251.

Sussman, K. 1985. Spectrum of defects in non-insulin-dependent diabetes mellitus. Am. J. Med. 79 (suppl. 79):1-5.

Terrettaz, J., and B. Jeanrenaud. 1983. In vivo hepatic and peripheral insulin resistance in genetically obese (fa/fa) rats. Endocrinology 112:1346-1351.

West, D. B., R. Rohlfing, R. Kava, and M. R. C. Greenwood. In press. Hepatic glucose production (HGP) is elevated in obese diabetic Wistar fatty (Wf) rats. Int. J. Obesity (abstr.).

Zucker, L. M., and T. F. Zucker. 1961. Fatty, a new mutation in the rat. J. Hered. 52:275-278.

Figure 1 Characteristics of WDF/TaDrt-fa obese (N = 7) and lean (N = 12) male rats. All were fed Purina formulation 5744C-1 ad libitum. Data are presented as mean + SE. A, Weight gain with age. B, Fed plasma glucose levels.

Figure 2 Characteristics of obese (N = 5) and lean (N = 5) male Vc:WDF/Ta-fa rats. Animals were fed Agway chow ad libitum until 21 weeks of age, then given a high-sucrose diet. Data are presented as mean + SE. A, Body weight curves. B, Fed plasma glucose levels.

Figure 3 Glycemic and insulinemic response to a two-week exposure to a powdered high-sucrose diet (68 percent of calories as sucrose) by obese male (N = 7) and female (N = 11) Vc:WDF/Ta-fa rats. Rats were 24-32 weeks old at the beginning of diet treatment. Data are presented as mean + SE.

Figure 4 A, Glycemic response to two-week supplementation with a 20 percent (w/v) sucrose solution by obese male (N = 7) and female (N = 6) Vc:WDF/Ta-fa rats. Rats were 23-31 weeks of age at the beginning of supplementation. B, Insulinemic response to the 20 percent sucrose supplementation. Data are presented as mean + SE.