Laboratory animals exhibiting obesity and diabetes syndromes

Animal models of diabetes

Spontaneous diabetes is a common occurrence in many animal species. In addition, animals can be rendered diabetic by a wide variety of experimental procedures. Diabetic animals may be regarded as models of the disease in man. However, such animals display a wide diversity of pathophysiology, and, in fact, no animal syndrome corresponds precisely to any type of diabetes in human subjects. The most common diabetes syndromes in animals occur in the context of obesity, hyperinsulinemia and insulin resistance. Many such syndromes remit spontaneously. Dietary restriction and weight reduction effectively reverse some of these syndromes, but in other cases only partial correction of the syndrome occurs. Diabetes in lean animals is less common. The diabetes of lean animals is more frequently characterized by hypoinsulinemia, ketosis and insulin dependence than is the case with obese animals. Diabetes may be produced experimentally by means of surgery, viral infection or the administration of various hormones and chemical agents. Both the spontaneous and experimental animal models have been used effectively to study the etiologies, complications, treatments and prevention of diabetes.

Serum thymic hormone activity in genetically-obese mice

1. Serum thymic hormone was assayed in genetically-obese (C57B1/6J ob/ob) mice and lean controls (+/+, +/-) of the same strain. 2. The thymic hormone activity was higher in the majority of the obese animals compared with non-obese mice. 3. The number of antibody-forming cells in the spleen expressed as a proportion of the total mononuclear cells was increased in the obese mice. 4. It is suggested that obesity is associated with significant changes in the thymic hormone levels which may alter the relative proportion of lymphocyte subsets and cell-mediated immunity.

The genetics of the glucose intolerance disorders

Genetic heterogeneity, the concept that diabetes can have many different causes, was first suggested by the existence of rare genetic syndromes with diabetes, ethnic differences in clinical features and genetic heterogeneity of animal models. Genetic heterogeneity is now considered to be firmly established by family, twin, metabolic, immunologic and HLA disease association studies that separate idiopathic diabetes into insulin-dependent types (juvenile-onset type) and noninsulin-dependent types (maturity-onset type). Further heterogeneity is being demonstrated within each of these broad groups of disorders--within insulin-dependent diabetes using the HLA antigens and immunologic studies, and within noninsulin-dependent diabetes using such criteria as obesity, insulin response, age of onset and chlorpropamide-primed alcohol-induced flushing. This heterogeneity has major implications for the research and care of our diabetic patients since the precise etiology, risk of complications and genetic counseling are likely to vary among these different disorders that result in diabetes.

Peripheral neuropathy in mouse hereditary diabetes mellitus. II. Ultrastructural correlates of degenerative and regenerative changes

The fine structural changes in some peripheral nerves and sensory ganglia from mice (C57BL/KsJ, db/db) with an hereditary diabetic syndrome, similar to human maturity-onset diabetes mellitus, were studied during development of the mild peripheral neuropathy. The abnormalities observed included axonal degeneration, disruption of myelin, accumulation of electro-dense material in axons, satellite cells and Schwann cells, increased frequency of pi granules of Reich in Schwann cells, enlarged mitochondria, and proliferated and thickened Schwann cell basal laminae. Distal hind limb nerves were most affected. Sensory ganglion neurons were normal except for occasional chromatolytic cells, so that nerve cell loss was not present in this peripheral neuropathy. Morphological indications of Schwann cell hyperplasia, hypertrophy, and axonal sprouting supported the contention that a continuous cycle of axonal degeneration and regeneration was occurring. The ultrastructural changes and accumulation of electron-opaque, lipid material suggested that a defect in lipid metabolism, secondary to the diabetic condition, could be an important factor in the peripheral neuropathy in the diabetic mouse.

The development of obesity in genetically diabetic-obese (db/db) mice pair-fed with lean siblings. The importance of thermoregulatory thermogenesis

The importance of reduced thermoregulatory thermogenesis as a mechanism for the high metabolic efficiency of the diabetic-obese (db/db) mouse has been investigated. Young db/db mutants were pair-fed to the ad libitum food intake of lean siblings for two weeks at two different environmental temperatures, 23 and 33 degrees C. At 23 degrees C, a temperature at which there is a substantial demand for thermoregulatory thermogenesis, the diabetic-obese animals deposited 51% more total energy and 75% more fat than the lean mice. At 33 degrees C (thermoneutrality) where there is no requirement for thermoregulatory heat, the mutants deposited 25% more fat than lean animals, but there was no significant difference in the total energy gain of the two groups. Pair-feeding resulted in a reduced protein deposition at both temperatures in the diabetic-obese animals compared to the lean. It is concluded that the high metabolic efficiency of the diabetic-obese mutant, like that of the obese (ob/ob) mouse, is caused by a low energy expenditure on thermoregulatory thermogenesis.

Role of Ca2+ in impaired insulin release from islets of diabetic (C57BL/KsJ-db/db) mice

The involvement of Ca2+ in the impaired insulin release of diabetic C57BL/KsJ-db/db mice was studied. Twenty-week-old severely hyperglycemic mice were compared to nondiabetic C57BL/KsJ mice as controls. Collagenase-isolated islets were maintained for 46 h in tissue culture allowing for equilibration at the same glucose concentration (8.3) mM). The insulin content of both types of islets was similar. In control islets preloaded during culture with 45Ca2+ glucose-induced insulin release was associated with increased 45Ca2+ effux. Islets from diabetic mice showed markedly reduced insulin response to glucose and a smaller increase in 45Ca2+ efflux. Because insulin release was strikingly potentiated by 3-isobutyl-1-methylxanthine (IBMX), even more than in control islets, there was no generalized release defect. In both types of islets, IBMX potentiation was accompanied by a further enhanced 45Ca2+ efflux, possibly suggesting that cAMP effects are associated with increased cytosol Ca2+% concentrations. As Ca2+ uptake was stimulated by glucose in both types of islets, a defect may lie in the mechanism by which glucose uses cellulr calcium to raise cytosol Ca2+ in the beta-cell of these diabetic mice.

Increased ATP inhibition of liver phosphofructokinase from genetically diabetic mice

Phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) was partially purified from the livers of genetically diabetic mice (C57BL/KsJ-db) and their lean littermates (C57BL/KsJ). These genetically diabetic mice have been shown to be hyperglucagonemic and to exhibit symptoms resembling those of maturity-onset diabetes in humans. Two isoenzymes of phosphofructokinase were obtained after DEAE-Sephadex chromatography of extracts of livers from either normal or diabetic animals. One of these isozymes, peak II, from the genetically diabetic mice was shown to be more sensitive to ATP inhibition at physiological pH than the peak II isozyme from the normal animals. In addition, the peak II isozyme from the diabetic mice exhibited decreased affinity for fructose 6-phosphate. The altered kinetic properties of phosphofructokinase from diabetic animals are markedly similar to those recently reported for liver phosphofructokinase isolated from normal animals after glucagon treatment. Our results suggest that increased glucagon levels in diabetes may lead to altered regulation of phosphofructokinase in this disease.

Glucose metabolism and recycling of radioactively labelled glucose in the Zucker genetically obese rat (fa/fa)

1. The glucose metabolism of conscious lean and obese rats of the Zucker strain was studied by using doubly labelled glucose ([6-3H,U-14C]glucose) given by intravenous injection as a single dose. Fed animals were used, allowing the study to be made in conditions favouring active lipogenesis. 2. At any given prior food intake (consumption during preceding 24 h), the irreversible glucose replacement rate, R0, was considerably higher in the growing obese rat (4-6 months old) when both of these variables were scaled in terms of the total body water of the animals. 3. When scaled in a similar way, the minimal mass of glucose (Mmin.) was also larger in the obese rats. The mean transit time, t, through the pool did not differ significantly between the two groups, but there was a tendency for this to be shorter in obese rats. 4. There was no difference in the proportion of 14C (derived from metabolized labelled glucose) that recycled as [14C]-glucose after passing through the pyruvate pool in the two groups of rats if the rate of recycling of radioactivity (Rc) was expressed as a percentage of R0.

Cytochemical correlates of structural sexual dimorphism in glandular tissues of the mouse

Circulating androgens are known to effect a sexual dimorphism of the submandibular gland and kidney of the mouse. Enzyme histocytochemical differences that correlate with these structural changes have been the subject of much study, especially in the kidney. In the present study, emphasis was placed on the hypogonadic effects of diabetes mellitus on the submandibular gland and kidney of C57Bl/KsJ db/db inbred mice with an autosomal recessive disease resembling maturity onset human diabetes mellitus. These glands of adult diabetic mice of both sexes were compared with those of unafflicted heterozygous littermates. The mitochondrial cytochrome oxidase and peroxisomal and cytoplasmic catalase were studied in their submandibular glands and kidneys. The parasympathetic innervation of the submandibular glands was studied by a histochemical method for acetylcholinesterase. The extensive differentiation of striated ducts of the submandibular gland into granular tubules in the postpubertal male mouse was readily evident with the cytochrome oxidase procedure. This differentiation resulted in ductal staining patterns characteristic of the sexes. Alteration of these patterns suggested that demasculinization or feminization was occuring in the male diabetic mice and that masculinization or virilization (defeminization) was occurring in the female diabetics. Similarly, in kidney, study of the parietal epithelium of Bowman's capsule revealed feminization in the male diabetics and masculinization in the female diabetics. With the catalase procedure, a dramatic sexual dimorphism was observed in the kidneys of the heterozygous unafflicted mice. Peroxisomal staining of epithelial cells of the proximal convoluted tubules was much more intense in the outer medulla of the male than of the female. In kidneys of the diabetics, the staining patterns again suggested that feminization of the male and masculinization of the female kidneys had occurred. On the other hand, neither a sexual dichotomy nor effects due to diabetes could be observed in the characteristic catalase staining observed in the luminal epithelial cells of submandibular gland distal ducts. The parasympathetic innervation of the submandibular gland, as revealed by the acetylcholinesterase method, was also markedly sexually dimorphic in the unafflicted mice. This was due to the more extensive innervation of the larger granular ducts characteristic of male than of the smaller striated ducts of the female. As a result of diabetes, the innervation and duct size decreased in the submandibular gland of the male, suggesting feminization, whereas they increased in the female suggesting masculinization. These changes were consistent with those observed in sumandibular gland with the cytochrome oxidase procedure. Attempts were made to interrelate all of the enzyme histochemical changes observed in submandibular gland and kidney with the weights of these glands, sex, gonadal weights, diabetic status and urinary protein excretion...

Analysis of genetic control of chylous ascites in ragged mice

Chylous ascites is a disorder visible as a white fluid in the peritoneal cavity of suckling mice. It is due to inadequate lymphatic drainage from the small intestine. An initial genetic study showed it to be a pleiotropic effect of ragged, Ra. There were four main studies. These involved seven major mutants segregating with ragged. Four of the mutants had no effect on chylous ascites, but two mutants linked with ragged, and one unlinked, showed a complex situation involving enhancement, inhibition, epistacy and other interactions. The overall phenotypic effects which these mutants are known to have do not explain how they produce their interaction with ragged in terms of chylous ascites. The studies also indicate the existence of a single major modifier controlling penetrance and expression, and there is evidence for cumulatively acting minor modifiers. In neonates the male sex is more liable to chylous ascites, and in adults this condition affects fertility and fecundity.

Thermoregulation in the diabetic-obese (db/db) mouse. The role of non-shivering thermogenesis in energy balance

1. Thermoregulation and non-shivering thermogenesis have been studied in the genetically diabetic obese (db/db) mouse. 2. At all environmental temperatures between 33 and 10 degrees C the body temperature of the diabetic mice was lower than that of the normal littermates, the difference varying from 1.1 degrees C at 33 degrees C to 4.5 degrees C at 10 degrees C. 3. At 4 degrees C the diabetic mice rapidly died (3.2h) of hypothermia while the normal mice maintained their body temperature within the normal range. 4. At 23 degrees C the diabetic animals exhibited a diurnal rhythm in body temperature which was similar in both phase and amplitude to the controls, but at every point throughout the 24h cycle the temperature of the mutants was lower by 1--2 degrees C. 5. The resting metabolic rate at thermoneutrality (33 degrees C) was higher per whole animal for the diabetics than for the normals. However, at temperatures below thermoneutrality the converse was observed; between 30 and 4 degrees C the RMR of the mutants was lower than the controls by approximately 25%. 6. The capacity for non-shivering thermogenesis in diabetic mice was only one-half that found in normal animals. 7. The diabetic mouse has abnormalities in thermoregulation and non-shivering thermogenesis which are similar to those found in the genetically obese (ob/ob) mouse. It is concluded that the high metabolic efficiency of the diabetic mouse, like that of the ob/ob mouse, can be explained by a reduced energy expenditure on thermoregulatory thermogenesis; this may represent a primary mechanism for the operation of the "thirfty genotype" associated with obesity and diabetes.

Obesity genes: beneficial effects in heterozygous mice

The mouse mutant genes obese (ob) and diabetes (db) cause similar obesity-diabetes states in homozygotes. These obesity syndromes are characterized by a more efficient conversion of food to lipid and, once stored, a slower rate of catabolism on fasting. Heterozygous mice, either ob/+ or db/+, survived a prolonged fast significantly longer than normal homozygotes (+/+); this suggests that the heterozygotes exhibited increased metabolic efficiency, a feature normally associated with both homozygous mutants. The existence of this thriftiness trait, if manifested by heterozygous carriers in wild populations, would lend credence to the thrifty gene concept of diabetes. Beneficial effects of normally deleterious genes may have played a role in the development of diabetes-susceptible human populations, as well as having provided the survival advantage that has allowed both the development and successful establishment of species in desert and other less affluent regions.

Carbohydrate metabolism in lean and obese Zucker rats

Carbohydrate metabolism was evaluated in lean and obese Zucker rats. Plasma glucose concentration, renal and hepatic gluconeogenesis, and hepatic glycogen content and rates of synthesis were investigated in 2-mo and 8-mo-old animals. Mild hyperglycemia was observed in obese Zucker rats compared to lean rats and was more pronounced in males than in females. Rates of glucose disappearance were normal in both female and male rats, although there was a trend toward decreased clearance in the male. Total organ hepatic and kidney PEPCK activity and kidney glucose production were elevated in obese compared to lean rats. Total organ hepatic glycogen levels and rates of glycogen synthesis were increased significantly in obese compared to lean, the increase being greater in males than females. The mild hyperglycemia present in obese Zucker rats is not associated with delayed disappearance of intravenously administered glucose, but may be due to the increased production of glucose by whole kidney and liver.

Studies on the body composition, fat distribution and fat cell size and number of 'Ad', a new obese mutant mouse

1. Studies have been performed on the body composition, the fat distribution, the fat cell size, and the 'observable' fat cell number of a new obese mutant, the Adipose (Ad) mouse. The serum glucose and insulin concentrations have also been investigated. All studies were undertaken with animals aged 6 months. 2. The obese animals weighed over 50% more than the lean, but there was no difference in the body or tail lengths. 3. The obese animals had an increase in the weight of the liver, but the increase was only proportional to the increase in the total body-weight. 4. The carcasses of the obese mice contained more water as well as more fat than those of the lean. In the males the fat content was 3.9 times greater, while in the females it was increased by 5.5 times. 5. The nitrogen content of the defatted dry carcass was the same in both lean and obese animals but the total body protein was higher in the obese. 6. Fat was dissected from four major depots, gonadal, abdominal, hind subcutaneous and interscapular subcutaneous (including brown adipose tissue), and each was substantially larger in the obese animals. This indicated that the additional fat of the Ad mouse was not localized to any particular site. 7. In Ad males there was no over-all increase in the observed number of adipocytes, all the extra fat being accommodated by an increase in fat cell size (3.8 times). However, in Ad females there was a 3.3 fold increase in the number of observable fat cells as well as a 2.2-fold increase in fat cell size. 8. Non-fasted obese animals were not hyperglycaemic, but there was a 5.3-fold increase in the concentration of serum insulin. Hyperinsulinemia in the presence of normoglycaemia suggested that the obese animals were insulin resistant.

Obesity: do fat cells from genetically obese mice (C57BL/6J ob/ob) have an innate capacity for increased fat storage?

Fat tissue from the genetically obese mouse (C57BL/6J ob/ob) and its lean littermate (+/?) was transplanted into lean hosts(+/+). Chemical induced obesity in the host mice caused no greater increase in the size of 'obese' fat cells than it did in the size of 'lean' fat cells. 'Obese' fat cells, therefore, have no innate capacity for increased fat storage.