Characterization of diabetes in the Chinese hamster

Retinal changes in mice spontaneously developing diabetes by Th17-cell deviation

Elevated level of interleukin (IL)-17, predominantly produced by T helper (Th) 17 cells, has been implicated in diabetic retinopathy (DR), but it remains unclear whether IL-17 is involved in the pathogenesis of DR. Ins2^Akita (Akita) mice spontaneously develop diabetes, and show early pathophysiological changes in diabetic complications. On the other hand, interferon-γ knock out (GKO) mice exhibit high differentiation and activation of Th2 and Th17 cells as a result of Th1 cell inhibition. In this study, Ins2^Akita IFN-γ-deficient (Akita-GKO) mice were established by crossbreeding Akita mice with GKO mice, and Th17-mediated immune responses on DR were investigated. Blood glucose levels (BGL) of Akita mice and Akita-GKO mice were significantly higher than those of age-matched wild type (WT) or GKO mice, and there was no significant difference in BGL between Akita and Akita-GKO mice. Relative mRNA expression of ROR-γt that is a transcriptional factor of Th17 cells but not GATA-3 that is for Th2 cells was significantly upregulated only in Akita-GKO mice compared with WT mice, and the proportions of IL-17 and IL-22-producing splenic CD4⁺ cells were significantly higher in Akita-GKO mice than in wild type (WT), Akita, or GKO mice. In the retina, mRNA expression of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 (ICAM-1) were increased in Akita-GKO mice more than in Akita or GKO mice, and statistically significant differences were observed between Akita-GKO mice and WT mice. Leukostasis in retinal vessels and ocular level of VEGF protein increased significantly in Akita-GKO mice compared with the other groups. Edematous change in the retinal surface layer, retinal exudative lesions depicted as areas of hyperfluorescence in fluorescein angiography (FA), and vascular basement membrane thickening in all layers of the retina were also observed in Akita-GKO mice at 9-week-old but not in age-matched Akita or GKO mice. These results suggested that Th17 cell-mediated immune responses might be involved in promotion of functional and morphological changes in the retina of mice spontaneously developing diabetes.

The Chinese or Striped-Back Hamster

Chinese hamsters are small rodents with a grayish black coat and a black dorsal stripe. Adult animals weigh approximately 39–46 gm, and measure approximately 9 cm in length. This species has been shown to be susceptible to a number of experimentally induced viral, bacterial, and parasitic infections. In recent years, the Chinese hamster's contributions as a laboratory animal have been largely overshadowed by the focus on its cell lines and the role it plays in scientific research and biotechnology. The Chinese hamster used in biomedical research is traditionally classified as Cricetulus griseus. It has several biological features that have helped promote its use in biomedical research and these attributes include its small size, polyestrous cycle, short gestation period, and low chromosome number. The Chinese hamster has a low incidence of spontaneous and endogenous viral infections. This species has been shown to be susceptible to a number of experimentally induced viral, bacterial, and parasitic infections. Chinese hamster-derived cells have played a major role in cytogenetic toxicity assays and the production of glycosylated therapeutic proteins. The behavior, research uses, and general toxicology of the Chinese hamster are summarized in this chapter.

Characterization of a mouse model of hyperglycemia and retinal neovascularization

One of the limitations of research into diabetic retinopathy is the lack of suitable animal models. To study how the two important factors--hyperglycemia and vascular endothelial growth factor--interact in diabetic retinopathy, the Akimba mouse (Ins2AkitaVEGF+/-) was generated by crossing the Akita mouse (Ins2Akita) with the Kimba mouse (VEGF+/+). C57Bl/6 and the parental and Akimba mouse lines were characterized by biometric measurements, histology, immunohistochemistry, and Spectralis Heidelberg retinal angiography and optical coherence tomography. The Akimba line not only retained the characteristics of the parental strains, such as developing hyperglycemia and retinal neovascularization, but developed higher blood glucose levels at a younger age and had worse kidney-body weight ratios than the Akita line. With aging, the Akimba line demonstrated enhanced photoreceptor cell loss, thinning of the retina, and more severe retinal vascular pathology, including more severe capillary nonperfusion, vessel constriction, beading, neovascularization, fibroses, and edema, compared with the Kimba line. The vascular changes were associated with major histocompatibility complex class II+ cellular staining throughout the retina. Together, these observations suggest that hyperglycemia resulted in higher prevalences of edema and exacerbated the vascular endothelial growth factor-driven neovascular and retinal changes in the Akimba line. Thus, the Akimba line could become a useful model for studying the interplay between hyperglycemia and vascular endothelial growth factor and for testing treatment strategies for potentially blinding complications, such as edema.

Natural course of diabetic peripheral neuropathy in spontaneous-onset diabetic Chinese hamsters

We investigated metabolic and pathological changes in the peripheral nerve of the spontaneous-onset diabetic Chinese hamster. Electrophysiological examination revealed that the motor nerve conduction velocity was significantly decreased at 10 months and afterwards, however, the F-wave latency was significantly increased at 5 months and afterwards. Concerning sciatic nerve contents of sorbitol, myo- and scyllo-inositol, the content of sorbitol was not significantly increased at 5 months, but, myo- and scyllo-inositol were significantly decreased at 5 months and thereafter. At 10 and 15 months, however, sciatic nerve content of sorbitol was significantly increased. On morphological examination, loss of large myelinated fiber and reciprocal increase in degenerative fiber were also seen in sciatic nerve, but not in tibial nerve, at 5 months. At 15 months, these morphological changes were also found in the tibial as well as the sciatic nerve. Thus, we may hypothesize that F-wave latency is useful in the detection of initial diabetic neuropathy, and that the initial pathological changes in diabetic neuropathy of diabetic Chinese hamsters are predominantly found in the proximal site of peripheral nerves.

Diabetes mellitus: stress, neurochemistry and behavior

Neurochemical alterations in several rodent models of insulin-dependent diabetes are compared and their relevance to behavioral and physiological pathology in the clinical disorder is discussed. In the majority of rodent models, reductions in metabolism of norepinephrine (NE), dopamine (DA) and serotonin (5HT) in the central nervous system (CNS) have been reported. While there are two reports of increased 5HT turnover in CSF or post-mortem brains of diabetic humans experiencing severe ketoacidosis, these patients were receiving insulin therapy. Insulin appears to have effects on monoamines opposite to that of chronic hyperglycemia. Both in rodent models and in clinical populations, there is widespread evidence of enhanced hormonal and behavioral responsiveness to stress. There are findings in rodent models indicating that hormonal responses to stress are related to CNS monoamine activity. The mechanisms responsible for both hormonal and CNS alterations in diabetes, as well as their involvement in behavioral pathology, can best be investigated further using animal models.

Increase in liver protein phosphatase-1 in spontaneously diabetic Chinese hamsters

Two broad-specifically protein phosphatases, termed protein phosphatase-1 (PrP-1) and protein phosphatase-2A (PrP-2A), accounting for all the hepatic activity regulating glycogen phosphorylase, were measured in spontaneously diabetic Chinese hamsters exhibiting persistent glycosuria. When compared with genetically related inbred sublines free of glycosuria, diabetic animals demonstrated approximately 25% increase in PrP-1 activity measured either in crude tissue extracts or in cytosols fractionated by ion-exchange chromatography. No significant alteration in total PrP-2A activity was observed in the diabetic animals. These findings indicate that a specific change in hepatic PrP-1 is associated with genetically acquired diabetes in Chinese hamsters. In contrast to reported data using animals with experimentally induced diabetes mellitus, hepatic PrP-1 was increased in the spontaneously diabetic Chinese hamsters. The data suggests that distinct alterations in PrP-1 and associated metabolic consequences are exhibited by different types of diabetes.

The influence of plasma insulin concentrations on tissue insulin levels in rodents: a study of the diabetic Chinese hamster and the ob/ob mouse

Immunoreactive insulin was measured in acid-ethanol extracts of kidney, brain, liver, and heart from genetically diabetic Chinese hamsters and their nondiabetic controls and from obese (ob/ob) mice and their thin littermates. Selected samples were filtered on Sephadex G-50 columns and the insulin concentration determined. There was a good correlation between the insulin level measured in the acid-ethanol extracts of tissues and the insulin level after gel filtration, suggesting that the concentration measured in the whole extract is representative of the true insulin content. The present data demonstrate that different extrapancreatic organs contain characteristic amounts of insulin that are often (sometimes several-fold) higher than the insulin level of plasma. The tissue insulin concentrations also exhibit a wide range of values, with occasional high values. The data also show a direct correlation between plasma and kidney insulins but no relationship between plasma and brain insulins and a mixed correlation among plasma and liver and heart insulins.

Diabetic Chinese hamsters: metabolic effects of long term guar gum consumption

The effect of 13 weeks of guar gum or cellulose diet consumption upon metabolic parameters was examined in diabetic and control adult Chinese hamsters. Diabetic hamsters displayed typical diabetic metabolic profiles. Both 8% guar gum and 8% cellulose diets maintained body weights in all 4 groups during the study. Diabetic and control hamsters fed guar gum drank less water as the study progressed. At weeks 9 and 13, diabetic hamsters fed guar gum excreted less urine compared to those fed cellulose. Diabetic hamsters fed guar gum had reduced urinary glucose excretion at weeks 1, 9 and 13 compared to those fed cellulose. Control hamsters fed either diet had normal urine volumes with only traces of glucose. Similar fasting plasma glucose levels were measured initially for all diabetic hamsters; all 3 subsequent measurements revealed lower levels for the group fed guar gum. Control hamsters had normal fasting plasma glucose levels. Comparable fasting plasma insulin levels were measured for all diabetic hamsters; these levels increased during the study. Control hamster fasting plasma insulin levels were 3 times higher and did not change. Throughout the study, diabetic hamsters fed guar gum consistently had healthier metabolic profiles than those fed cellulose.

Insulin, glucagon, and somatostatin release from the prediabetic Chinese hamster

Diabetes mellitus in the adult Chinese hamster is characterized by subnormal pancreatic insulin release in vitro, decreased insulin content, and lack of obesity. The cause of the islet B-cell failure is not clear. We measured insulin, glucagon, and somatostatin release from in vitro perfused pancreases of young (mean age 10 and 20 weeks), genetically diabetic animals (subline AC, mean plasma glucose 8.0 and 16.6 mmol/l, respectively). Compared to age- and sex-matched normal hamsters (subline M, mean plasma glucose 5.3 mmol/l), the younger diabetic animals had a significantly elevated mean plasma glucose level, but net in vitro pancreatic release of insulin, glucagon, and somatostatin was normal. Pancreatic content of insulin and glucagon was also not significantly different from normal. At age 20 weeks, when the plasma glucose of the diabetic animals was even more elevated, pancreatic content and release of insulin were significantly subnormal, whereas glucagon and somatostatin release were normal, and pancreatic content of glucagon was normal. In a similar group of young (mean age 10 weeks) diabetic animals, non-fasting plasma insulin levels were within the normal range, but the corresponding glucose levels were excessive in most of the animals (13 out of 19). In conclusion, 10-week-old diabetic hamsters show mild hyperglycaemia which cannot be accounted for directly by decreased pancreatic release in response to a glucose plus arginine stimulus in vitro. Decreased ability of the B cell to respond in vivo to hyperglycaemia or peripheral resistance to insulin may contribute to later B-cell failure in the older diabetic hamster.

Peripheral neurology of the diabetic Chinese hamster

Genetically diabetic Chinese hamsters were examined anatomically and physiologically for evidence of peripheral neuropathy. Control animals were from non-diabetic strains. Conduction velocities in both motor and sensory components of the hind limb nerves were reduced 16-22% in diabetic compared with control hamsters. However, there was no reduction in nerve fibre diameters or other signs of abnormal morphology that could be correlated with these physiological effects. It is concluded that the diabetic hamster is useful as a model of human diabetic peripheral neuropathy, but the analogy is not precise. The neuropathy of moderately diabetic hamsters is generally less severe than human diabetic neuropathy in its clinical stages.

Morphometric evaluation of the hypothalamic-ovarian axis of the ketonuric, diabetic Chinese hamster: relationship to the reproductive cycle

The relationship between diabetes and the morphological alterations which occur in hypothalamic and ovarian tissue was examined in the long-term, ketonuric-diabetic Chinese hamster. Matched diabetic and non-diabetic control hamsters were inspected daily for changes in the reproductive cycle by vaginal lavage. On dioestrus, animals were perfused, the hypothalamus and ovaries collected, prepared for microscopy and morphometrically analyzed. The nuclei in the medial basal hypothalamus of diabetic hamsters exhibited a decreased area (p less than 0.01) and neuronal population (p less than 0.05-0.01) compared with controls. The ovaries of the diabetic animals had a reduced follicular population (p less than or equal to 0.05) and an increased atresia rate (p less than or equal to 0.05) compared with controls. In addition, all diabetic hamsters were acyclic. In diabetic animals, the corpora luteal cells contained a reduced lipid content (p less than or equal to 0.001) which was possibly functionally related to a significant decline in serum progesterone levels (p less than or equal to 0.01). Based on these results it is suggested that the hypothalamic-ovarian axis is both morphologically and functionally impaired in the diabetic hamster.

Insulin and glucagon release in the diabetic Chinese hamster: differences among inbred sublines

Release of insulin and glucagon from perfused pancreases in vitro of 40 normal male and female Chinese hamsters (from one inbred subline) and 110 male and female diabetic hamsters (from three inbred sublines) was measured in response to glucose plus arginine, theophylline alone, or potassium alone, in order to determine if differences in hormone secretion exist among different diabetic sublines. Glucose plus arginine and potassium produced subnormal insulin responses in all three diabetic sublines, whereas theophylline induced 'normal' or above normal insulin responses. Excessive glucagon release was consistently seen in only one diabetic subline. The female normal animals showed greater insulin release than the male normal hamsters in response to glucose plus arginine. This sex difference was not seen in the diabetic animals.

Wound healing in normal and diabetic Chinese hamsters

Wound healing was examined in normal and diabetic, non ketotic Chinese hamsters by morphological and morphometric methods. Dermal, perforating wounds were made in the ears of the hamsters and the response to injury was evaluated in tissue biopsies. The response in normal hamsters was characterized by vascular and cellular migration and pronounced infiltration of polymorphonuclear leukocytes into the area closest to the wound (zone 1). The transition region (zone 2) between wounded and non-wounded tissue was infiltrated primarily by fibroblasts and capillaries. In wounds from diabetic hamsters, 8 h after injury, there was less cellular infiltration (fibroblasts 49%, polymorphonuclear leukocytes 48% of control) and vascular proliferation (47% of control). In the late phase of healing (16 h after injury) the vascular (87% of control) and polymorphonuclear leukocyte (103%) responses in diabetic wounds were not significantly different from control in zones 1 and 2. Wounds from diabetic hamsters also showed considerable oedema (143% of control) in zones 1 and 2, which was accompanied by vascular degeneration and necrosis. At 16 h the collagen content of diabetic wounds was also decreased (54% of control). Increased oedema with reduced vascular proliferation and cellular infiltration in the early healing period characterises the response to injury in the diabetic Chinese hamster.

Prevention of diabetes in rats by bone marrow transplantation

Hyperglycemia, hypoinsulinemia and ketonemia often develop abruptly in previously normal young "BB" rats. The syndrome mimics human juvenile diabetes closely and is, thus, appropriate for assessing pancreatic transplantation. Transplantation of islet cells from closely histocompatible Wistar Furth (WF) donor resulted in permanent normoglycemia when immunosuppression with ALS was given. However, when islet cells from nondiabetic "BB" donors were transplanted to nonimmunosuppressed diabetic "BB" recipients, only transient normoglycemia followed. Transplantation of WF islets cells also failed in diabetic "BB" rats which were tolerant of WF antigens, again suggesting destruction of transplanted islet cells by the original disease process-possibly autoimmunity. Evidence for autoimmunity was strengthened by the finding that newly diabetic "BB" rats could be rendered normoglycemic by immunosuppression. Since genetic susceptibility to spontaneous autoimmune diabetes is unique to some members of the "BB" stock, an attempt was made to alter their vulnerability by modifying their cellular immune system. Accordingly, 50 million bone marrow cells from WF donors were inoculated into half the newborn members of "BB" litters, leaving the littermates as unmodified controls. Most bone marrow recipients were protected, only four of 37 (10.8%) ever becoming diabetic, while the incidence of diabetes in noninoculated littermates was 22 of 39 (56.4%). The ultimate goal in human diabetes, which also seems very likely to be an autoimmune disease, may not be replacement of destroyed islet cells but identification of potentially susceptible children and prevention of islet destruction by immunologic manipulation.

Hepatic carbohydrate metabolism in the spontaneously diabetic Bio-Breeding Worcester rat

The effects of diabetes on hepatic carbohydrate metabolism were investigated in spontaneously diabetic Bio-Breeding Worcester (BB/W) rats. The juvenile-onset-type syndrome displayed by these animals is characterized by beta-cell destruction with subsequent ketosis-prone insulinopenia. Livers from diabetic animals demonstrated increased adenosine 3',5'-cyclic monophosphate levels but subnormal total protein and glycogen content. Isolated perfused livers of diabetic BB/W rats demonstrated an increased rate of glucose production from [14C]lactate and an impaired rate of glycogen synthesis. These data were consonant with hepatic enzyme studies demonstrating markedly increased activities of component gluconeogenic (glucose-6-phosphatase, fructose-1,6-diphosphatase, phosphoenolpyruvate carboxykinase) and glycogenolytic (glycogen phosphorylase) enzymes with decreased activities of glycolytic (hexokinase, pyruvate kinase) and glycogenic (glycogen synthase) enzymes. These findings agree with previous studies using alloxan- and streptozotocin-induced diabetic animals and suggest that accelerated hepatic gluconeogenesis and impaired glucose utilization are pathognomonic of all insulin-deficient diabetic 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.

Renal glucosyltransferase activity in highly-inbred spontaneously diabetic Chinese hamsters

A modified glucosyltransferase assay using degraded gelatin as acceptors was found to be enzyme concentration- and time-dependent in the Chinese hamster kidney extracts. In 54 Chinese hamsters selected from 7 highly inbred sublines with or without spontaneous glycosuria, the glucosyltransferase activity (0.78-3.25 unit/g) in the kidney was found to be significantly correlated (P = 0.0002) to blood sugar concentrations (60-475 mg/dl). However, subline-dependent variation in glycosyltransferase activity was also evident and, in animals from 2 of the 5 diabetic sublines, similar activity of glucosyltransferase was found in their kidneys as in those of nondiabetic animals. It was concluded that renal glucosyltransferase activity was affected by blood sugar level as well as by genetically determined factor(s).

Ultrastructural study of the mitochondria in the skeletal muscle fibers in the diabetic Chinese hamster

An ultrastructural study of skeletal muscle fiber biopsies from the tongue and soleus muscle of diabetic Chinese hamsters revealed the presence of lipid droplets within the muscle fibers. These droplets often were found in the cyptoplasm near mitochondira, sometimes inside or surrounded by one or more mitochondria. Glycogen granules were found in great quantities in the cytoplasm of the tongue and soleus muscle. Granules which appeared to be glycogen were also found within the mitochondria of the tongue muscle.

Decreased cyclic AMP and insulin responses to glucose in pancreatic islets of diabetic Chinese hamsters

The dose as well as the time kinetics of insulin and adenosine-3',5'-monophosphate (cyclic AMP) responses to glucose were compared in pancreatic islets isolated from normal and diabetic Chinese hamsters. The insulin content in diabetic islets was about one-half that in normal islets. Insulin release in diabetic islets incubated for 10 min with glucose 60-1000 mg/100 ml was from one-third to one-half that in normal islets. Glucose 1000 mg/100 ml stimulated three-fold increases in insulin release without increasing the accumulation of [3H] cyclic AMP in either normal or diabetic islets prelabelled with [3H] adenine. However, in the presence of 1.0 mM of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), glucose 150 mg/100 ml elicited significant increases of insulin release (+ 134%) and [3H] cyclic AMP accumulation in islets (+ 44%) and incubation medium (+ 48%) of islets of normal but not diabetic hamsters. Also, in perifusion experiments with 0.1 mM IBMX, glucose 500 mg/100 ml produced threefold greater increases in insulin release and two-fold greater increases in efflux of cyclic AMP in normal than diabetic islets. By contrast with the lesser effects of glucose in diabetic islets, 1.0 mM IBMX increased islet and medium cyclic AMP, as well as insulin release, similarly in normal and diabetic islets. It is suggested that the impairment of glucose-induced insulin release in islets of the diabetic Chinese hamster may be due to a defective interaction of glucose with the adenylate cyclase-cyclic AMP system in the pancreatic B cell.

A study of the morphological changes in the small intestine of the spontaneously diabetic Chinese hamster

Several morphological changes were observed microscopically in the small intestine of some diabetic Chinese hamsters. Although some alterations lacked statistical significance due to variation, most diabetics displayed a greater incidence and severity compared with nondiabetic controls. The following structural deviations were seen in the small intestines of some diabetics: increased surface area, elevated number of goblet cells per villus, decreased muscle thickness with connective tissue infiltration, reduced number of Auerbach's plexuses, lymphocyte aggregations accompanied by blunted villi, blood vascular lesions and deformed villi due to excessive loss of epithelial cells.

Diabetogenic effects of N-nitrosomethylurea with special regard to species variations

The effect of N-nitrosomethylurea on the blood-glucose and the pancreatic islet light microscopic picture was studied in the Chinese hamsters, golden hamsters, guinea pigs, mice, rats and sand rats. The Chinese hamsters were most susceptible. Only in this species did a dose of 50 mg/kg body weight cause blood-glucose elevations and pancreatic islet damage. At a dose of 100 mg/kg body weight of N-nitrosomethylurea, blood-glucose elevations were recorded in the golden hamster together with damage to the islets and the exocrine pancreatic parenchyma. A toxic dose of 200 mg/kg body weight resulted in hyperglycemia and islet cell destruction in the rat and in slight alterations in the islets of mice. N-nitrosomethylurea was non-diabetogenic to guinea pigs and sand rats. The ethyl derivate of nitrosourea was less toxic and diabetogenic to the Chinese hamsters in comparison with the methyl derivate.

Influence of the mutation "diabetes" on insulin release and islet morphology in mice of different genetic backgrounds

Mice, 7-8-mo old, of the C57BL/KsJ-db strain and homozygotic for the mutant gene db, exhibited marked hyperglycemia and moderately elevated serum insulin levels. Light and electron microscopy provided evidence of a slightly decreased proportion of beta cells in the pancreatic islets, irregular islet architecture with intraislet ducts, and degenerative as well as hypertrophic changes in the individual beta cells. As a rule, islets microdissected from these mice did not release insulin in response to glucose, theophylline, iodoacetamide, or chloromercuribenzene-p-sulphonic acid. The absence of secretory responses was not simply due to lack of insulin. Although the islet content of insulin was decreased in C57BL/KsJ-db/db mice, the remaining amount was severalfold larger than that released from stimulated islets of normal controls. Another mutation, db(2J), an allele of db with identical phenotypic expressions in the C57BL/KsJ strain, was studied on the genetic background C57BL/6J. In contrast to the severely diabetic C57BL/KsJ-db/db animals, the C57BL/6J-db(2J)/db(2J) mice were characterized by highly elevated serum insulin levels and only moderate hyperglycemia. Their endocrine pancreas was enlarged and showed an increased proportion of beta cells. Like the islets of normal mice, those of C57BL/6J-db(2J)/db(2J) mice responded to glucose and chloromercuribenzene-p-sulphonic acid, the glucose-induced responses being potentiated by theophylline or iodoacetamide. C57BL/KsJ-db/db mice should provide a valuable model for studying defects in insulin secretion in relation to diabetes mellitus. Mice of the C57BL/6J strain offer a control material that may help to elucidate the dependence of the insulin secretory defect on the background genome.

Abnormal secretion of insulin and glucagon by the in vitro perfused pancreas of the genetically diabetic Chinese hamster

Hereditary insulin-deficient diabetes mellitus occurs in certain sublines of nonobese Chinese hamsters. Several characteristics of this syndrome are similar to those seen in insulin-deficient human diabetics. Therefore, to characterize pancreatic islet function, dynamic insulin and glucagon release from normal and nonketotic diabetic hamster pancreases in response to glucose (300 mg/100 ml) and theophylline (10 mM), infused singly and together, was studied in vitro.20-min glucose infusions of normal hamster pancreases caused biphasic insulin release, consisting of a rapid first peak and a gradually rising second phase, similar to that reported for man in vivo. Both phases were significantly reduced in the diabetic pancreases. Theophylline alone stimulated similar nonphasic insulin release in both the normal and the diabetic pancreases. Glucose and theophylline together caused greater insulin release than either stimulant alone in both normals and diabetics; however, the diabetic response was still subnormal. Glucose suppressed glucagon release from normal pancreases; suppression was significantly impaired in diabetics. Theophylline stimulated nonphasic glucagon release in both the normals and diabetics. Glucose partially suppressed the theophylline-stimulated release in both groups.Insulin/glucagon molar ratios of the diabetics were consistently subnormal, although individual hormone levels often overlapped into the normal range. IN SUMMARY, THE PANCREASES OF GENETICALLY DIABETIC CHINESE HAMSTERS PERFUSED IN VITRO SHOWED: (a) decreased first and second phase insulin release in response to glucose-containing stimuli-only partially ameliorated by theophylline-, and (b) impaired suppression of glucagon in response to glucose, resulting in (c) a decreased insulin/glucagon molar ratio. These data support the suggestion that both alpha and beta cells of diabetic pancreases may be insensitive to glucose.