Alloxan-treated Rats Research Articles

Fetal development in alloxan-treated rats

The effect of alloxan on embryo and fetal development in rats was evaluated. Alloxan was injected intraperitoneally (ip) in pregnant rats at doses of 80 to 150 mg/kg at Day 0 (day of fertilization), and 110 mg/kg at Day 4 of pregnancy. Hyperglycemia was rarely produced at alloxan doses from 80 to 100 mg/kg, and the frequency of malformations observed was low. Higher doses (110 to 150 mg/kg) caused severe hyperglycemia, and maternal or embryonic death. When 110 mg/kg was administered on Day 4 of gestation (the day before embryo implantation), all rats had resorption nodules and litters with embryos with delayed growth. We recommend the induction of diabetes mellitus on Day 4 of pregnancy for studies of diabetes–gestation interaction.

Early manifestations of nephropathy in alloxan-treated rats

An early stage of diabetic nephropathy was studied. Rat renal function was evaluated by clearance techniques, 7 or 15 days after alloxan administration (groups A7 and A15). Significant diminutions of glomerular filtration rate (inulin clearance) and p-aminohippurate clearance were observed in alloxan-treated rats. Diabetic animals presented glucosuria and enhanced water excretion. A natriuretic response was only observed in A15-rats. Arterial pressure increased along time, and enlarged lipid deposits in glomeruli and vessels of A7-kidney sections were observed. Thus, a vascular compromise at this time was suggested. To better characterize the set up of the renal dysfunction, other studies were performed in A7-group. Urinary protein excretion remained unchanged while a higher level of glycosylation of urinary proteins was observed in A7-rats. Histological studies revealed a normal general morphology in kidneys from diabetic rats. Immunohistochemical analysis in renal sections showed enlarged deposits of fibronectin in glomeruli and interstitium of alloxan-treated rats. Higher myeloperoxidase activity was observed in renal cortex from diabetic animals indicating leukocytes infiltration.These results indicated that 7 days after hyperglycemia induction, the animals presented a renal dysfunction characterized by hemodynamic alterations associated with vascular and glomerular structural impairments, without modifications in tubular function. The higher level of protein glycosylation and the inflammatory process at this early stage could be responsible for the beginning of diabetic nephropathy.

Effect ofAgarista mexicana andVerbesina persicifolia on Blood Glucose Level of Normoglycaemic and Alloxan-diabetic Mice and Rats

Blood glucose levels of normal and alloxan-treated diabetic mice and rats were determined after oral administration of various doses of the chloroform extracts of A. mexicana and V. persicifolia. From the data obtained, it is concluded that the oral administration of 100 and 150 mg/kg of chloroform extracts of these plants produced a significant hypoglycaemic effect in normal as well as in diabetic mice and rats. In addition the extracts altered glucose tolerance in alloxan induced diabetic rats, enhanced glucose uptake in skeletal muscle and significantly inhibited glycogenolysis in the liver. These results indicate that the hypoglycaemic effect may be similar to tolbutamide.

Alloxan diabetes reduces pleural mast cell numbers and the subsequent eosinophil influx induced by allergen in sensitized rats.

Alloxan damages insulin-producing cells and has been used as an inducer of experimental diabetes in several animal species. In this study, administration of alloxan (40 mg/kg, i.v.) to rats was followed by a selective and time-dependent reduction in the number of pleural mast cells (50 +/- 2.2%, p < 0.01; mean +/- SEM), while mononuclear cell and eosinophil counts were not altered. As compared to naive rats, the reduction in mast cell numbers was first noted 48 h following alloxan administration and remained unaltered for at least 60 days. It is noteworthy, that the depletion in the mast cell population was not accompanied by alterations in the total amount of histamine stored per cell. Sensitized rats turned diabetic by alloxan treatment performed 72 h before challenge showed a less pronounced antigen-induced mast cell degranulation compared to nondiabetic rats. Moreover, rats injected with alloxan 72 and 48 but not 24 h before challenge, reacted to allergenic challenge with 50% reduction in the number of eosinophils recruited to the pleural cavity within 24 h. We found that the less pronounced eosinophil accumulation did not relate to an intrinsic cell locomotor abnormality since eosinophils from diabetic rats presented similar chemotactic responses to LTB4 and PAF in vitro as compared to matching controls. Insulin (3 IU/rat) restored basal levels of mast cells and reversed the subsequent inhibition of allergen-induced pleural eosinophilia, suggesting a causative relationship between these phenomena. Treatment with insulin also significantly increased the number of mast cells in the pleural cavity of naive rats (from 637 +/- 57 to 978 +/- 79 x 10(3) cells/cavity, p < 0.001). Consistently, previous depletion of mast cells by means of local treatment with compound 48/80 significantly reduced the antigen-induced eosinophil recruitment in sensitized animals. We conclude that the reduction in the pleural mast cell population noted in alloxan-treated rats could be directly implicated in the diminished pleural eosinophil influx following allergen challenge. This hyporesponsiveness is independent of an intrinsic abnormality of cell chemotaxis, but can be imitated by local mast cell depletion.

Prevention of diabetes by thymic hormone in alloxan-treated rats

We investigated the effects of facteur thymique sérique (FTS), a thymic peptide hormone, on alloxan- and streptozotocin-induced diabetes in rats. Pretreatment with intravenous injection of FTS significantly suppressed both alloxan- and streptozotocin-induced hyperglycemia. The effects of FTS were time dependent. FTS suppressed hyperglycemia in a dose range of 1–6600 μg/kg. Alloxan-induced hyperglycemia was completely prevented when FTS was injected in doses of 40–50 μg/kg 1 min before injection of alloxan. Histological examination of islet areas showed that alloxan-induced destruction of β-cells was inhibited by FTS. FTS had no significant effects on lymphocyte subsets and immunity-related cells or on plasma superoxide dismutase activity and total glutathione level. The blood half-life time of exogenously injected FTS was short (2–3 min), indicating acute internalization of FTS into pancreatic β-cells. Our results suggested that FTS acutely and directly blocks some initial effect of alloxan, preventing the destruction of β-cells.

Growth and development of bone mass in untreated alloxan diabetic rats. Effects of collagen glycosylation and parathyroid activity on bone turnover

Body and skeletal growth and development were studied in alloxan-treated and age-matched control rats, between 3 and 23 weeks of age. For both groups the growth of the skeletal and body weights were in phase, with a maximum at 7 weeks of age. The growth data was assessed according to Parks' theory of feeding and growth. Alloxan-treated rats showed an important reduction in body and bone mass, with a greater impact on soft tissues. As expected, the asymptotic body and skeletal weights were reduced respect to controls. The time needed to attain 63% of mature food intake (Brody's ‘time constant’) was also reduced, indicating that maturation occurred at an earlier age than controls. The diabetic state is characterized by a reduced food conversion efficiency. Despite hyperfagia, alloxan-treated rats showed circa one-half the body and skeletal weights of age-matched controls. The following adverse effects of alloxan diabetes on bone tissue were observed: (a) a decrease in trabecular bone volume (femoral metaphyses) and cortical width (femoral diaphyses), (b) increased bone collagen glycosylation as a function of extracellular glucose concentration, (c) increased resistance of bone collagen to collagenase hydrolysis, (d) decreased rate of bone resorption except under strongly stimulated parathyroid function, (d) significantly lower ashes/bone matrix ratio in diabetic rats with more than 10 weeks of diabetes, and (e) no histological evidence of osteomalacia.

A new diabetes model induced by neonatal alloxan treatment in rats

Rats treated with streptozotocin (STZ) during the neonatal period have been used as a model of non-insulin-dependent diabetes mellitus. The present study was designed to produce another diabetes model by substituting alloxan for STZ. Male Sprague-Dawley rats of 2, 4 or 6 days of age were injected intraperitoneally with 200 mg/kg of alloxan monohydrate after 16 h fast. Control rats received vehicle alone at 6 days of age. Non-fasting plasma glucose levels in alloxan-treated rats significantly increased after 8 weeks as compared with control, as the age of alloxan treatment advanced (6.6 ± 0.2 (S.E.M.) mM in control, 8.3 ± 0.3 mM in 2 days, P < 0.05, 9.8 ± 0.9 mM in 4 days, P < 0.05, 17.1 ± 3.5 mM in 6 days, P < 0.05). For the long-term observation, alloxan-treated rats were divided into mild and severe diabetes groups. Hyperglycemia persisted in both groups until 52 weeks (6.5 ± 0.1 mM in control, 10.3 ± 0.7 mM in mild diabetes group, 25.3 ± 3.6 mM in severe group), but significant albuminuria developed only in severe diabetes group. The diabetogenicity of alloxan rapidly increased during the neonatal period, and the neonatal alloxan diabetes model may be useful for studying chronic diabetic complications.

Regulation of the anorectic drug recognition site during glucoprivic feeding

The acute effects of 2-deoxy-D-glucose (2-DG)-induced glucoprivic feeding on the anorectic drug recognition site and Na +K + -ATPase in the brain were examined in adult rats and in lean and genetically obese mice. The marked hyperglycemia and the induction of feeding caused by the administration of 2-DG to satiated rats and lean mice were associated with significant increases in Na +K +-ATPase activity, and in [ 3H]ouabain binding and [ 3H]mazindol binding to the anorectic drug recognition site in hypothalamic membranes. Basal and 2-DG-stimulated levels of blood glucose were significantly correlated to the levels of hypothalamic [ 3H]ouabain ( r = + .91, p<0.01) and [ 3H]mazindol ( r = + .87, p<0.01) binding. A significant correlation ( r = .74, p<0.05) was also observed between [ 3H]mazindol binding and [ 3H]ouabain binding supporting the hypothesis that these hypothalamic binding sites are functionally coupled in their response to circulating glucose. Following the intracerebroventricular (ICV) administration of the diabetogenic drug alloxan, 2-DG did not stimulate feeding or increase [ 3H]mazindol and [ 3H]ouabain binding sites in the hypothalamic paraventricular area. Since 2-DG still caused hyperglycemia in alloxan-treated rats, alloxan-induced inactivation of glucoreceptor mechanisms led to an uncoupling of the anorectic drug recognition site from a hypothalamic glucostat. In genetically obese mice (ob/ob), 2-DG also could not induce feeding or increase hypothalamic [ 3H]ouabain or [ 3H]mazindol binding, despite a significant hyperglycemic response. In contrast, 2-DG did increase feeding and the binding of [ 3H]ouabain and [ 3H]mazindol to the hypothalamus of lean littermates. The dissociation of the anorectic drug recognition site from blood glucose responses to 2-DG suggests that the glucoprivic feeding response in obese mice is impaired. In conclusion, the [ 3H]mazindol recognition site and the neuronal Na +K +-ATPase labelled by [ 3H]ouabain binding constitutes a glucoreceptive system which in response to changes in circulating glucose levels modulates feeding. Since the coupling of this anorectic ding recognition site to brain glucostats is defective in genetically obese mice, this system may have an important role in pathological hyperphagia and the development of obesity.

Urinary bladder innervation in experimental diabetes

Autonomic neuropathy is a key factor in many human diseases including sudden cardiac death, gastrointestinal and urinary bladder dysfunction, and sexual impotence. Among the causes of autonomic nerve dysfunction, diabetes [12,20,26] and Chagas disease [13,27,39] are the most frequent. In human diabetics, urinary bladder function is often abnormal [1,7,10], although patients may be unaware of specific symptoms. Clinical features and morphological analysis of bladder nerves support the hypothesis that damage to the afferent (sensory) pathway results in a defective perception of bladder filling, which leads to a decrease in the reflex activity of the detrusor muslce [1,8,25]. We studied the alterations in the autonomic nervous system in various experimental models of diabetes including the obese db/db mouse [40,41], alloxan-treated rats [28-30], and BB rats with spontaneous insulin-dependent diabetes [31,32]. We focused on the urinary bladder of diabetic rats, since the autonomic innervation of this organ is a key factor regulating its function. Bladder contraction is governed by a reflex arch initiated by mechanoreceptors in the bladder wall. When stimulated by the pressure of filling, these receptors relay a message towards the spinal cord. Here they contact efferent fibers which, in turn, stimulate the muscle fibers of the bladder wall causing

Calcium metabolism of rats with varying degrees of insulinopenia

This paper reports an investigation designed to determine the influence of varying degrees of insulinopenia upon the calcium metabolism of actively growing, alloxan-treated rats fed diets with three levels of calcium. A significant reduction in the skeletal mass (in absolute terms) was observed one month after alloxan administration in rats fed diets with normal or high calcium contents. The impact of insulin deficiency was greater on bone collagen than on the mineral mass, as shown by the increased calcium/hydroxyproline ratio. Alloxan-treated rats showed rather increased levels of PTH which was at variance with respect to control animals and unrelated to the calcium content of the diet. In spite of the high PTH levels, diabetic rats showed significantly diminished rates of bone Ca accretion and resorption. In addition, the animals fed the diet with the normal Ca content, showed significantly reduced areas of osteocytes lacunae and hypocalcemia after 24 h of fasting. The overall information obtained indicates that, in the rat, insulin deficiency more pronouncedly affects organic matrix than mineral turnover. The diabetic state is characterized by an impaired reponse of bone tissue to physiological stimuli, which is attributed to defective cellular activity caused by insulin deficit. Diminished bone resorption is considered to be an adaptative response to preserve bone mass.

Enhanced apomorphine-induced hypothermia in alloxan-treated rats.

Previous studies have indicated that drug-induced experimental diabetes is associated with increased receptor binding in the rat brain. The purpose of this study was to determine whether the dopamine receptor agonist apomorphine (APO) might produce an accentuated hypothermic response in rats rendered diabetic by alloxan (ALX) treatment. In a previous study, however, the only controls used were ALX-treated rats that failed to develop glycosuria. Therefore, in this study, APO (0.5 mg/kg IP) was administered to ALX-diabetic and non-diabetic as well as saline-treated control rats to ascertain whether the APO responsiveness of ALX-non-diabetic rats was comparable to that of saline control animals. ALX-diabetic rats experienced significantly greater hypothermic response to APO than did the saline control animals. Although ALX-non-diabetic rats were similar to the saline control animals in body weight and blood glucose levels, they too were hyperresponsive to APO. These findings indicate that pancreatic injury from ALX, while not always sufficiently severe to produce overt diabetes, does appear to induce an hyperresponsiveness to APO-induced hypothermia in a manner similar to that observed in severely diabetic animals.

Some peroxisomal proliferators enhance membrane fluidity of liver peroxisomes.

The membrane fluidity of liver peroxisomes from normal and clofibrate-treated rats was investigated by using a fluorescence probe, 1-anilinonaphthalene-8-sulfonate (ANS). The excitation maximum of the probe was changed from 347 to 380 nm and the emission maximum from 493 to 463 nm in the presence of peroxisomes, and fluorescence intensity was enhanced more than 50 times. These results suggest that ANS was bound to the peroxisomal membrane. Fluorescence depolarization (P-value) was determined with such ANS-labeled peroxisomes. The P-values of peroxisomes from both normal and clofibrate-treated rats gradually decreased with increasing temperature, but that of clofibrate-treated peroxisomes was always smaller than that of normal peroxisomes. Pvalues were observed at 37°C for 60 min. The average P-value of normal peroxisomes was 0.270, while that of clofibrate-treated peroxisomes was 0.248. These results indicate that the membrane fluidity of liver peroxisomes in increased by the treatment with clofibrate. Treatment of rats with another inducer of liver peroxisome proliferation, di(2-ethylhexyl)phthalate, had an effect similar to that of clofibrate. However, alloxan-treated (diabetic) rats showed no change of peroxisomal membrane fluidity.

Glucagon satiety: Diurnal variation after hepatic branch vagotomy or intraportal alloxan

Hepatic vagotomized and hepatic portal alloxan-injected rats and their controls were tested for glucagon satiety at three time points during the circadian photoperiod: 6 hr into the light cycle with no food deprivation using a palatable liquid food; at the onset of the dark cycle after 6 hr food deprivation using pelleted rat chow; and 3 hr into the dark cycle after 9 hr food deprivation using pelleted chow. Glucagon failed to suppress intake in hepatic vagotomized and alloxan-treated rats when tests were conducted during the light cycle or at the onset of the dark cycle. In contrast, in tests conducted 3 hr into the dark cycle, glucagon suppressed food intake significantly in both hepatic vagotomized and alloxan-treated rats. Glucagon suppressed food intake significantly in controls in all tests. These results indicate that the hepatic vagus is not the sole mediator or glucagon satiety. Moreover, the fact that alloxan-treated rats and hepatic vagotomized rats responded in a similar manner to glucagon at all testing times suggests that hepatic portal alloxan treatment damages hepatic vagal fibers.

Amygdaloid kindling in alloxan-diabetic rats.

Wistar rats, made diabetic by intravenous administration of alloxan, 40 mg/kg, were submitted to amygdala kindling. The EEG and behavioral responses elicited by stimulating the amygdala nuclei in these animals were compared with those observed in control rats. Alloxan-treated rats required more stimulation to kindle, had increased duration of afterdischarges (AD), presented intense interictal spiking, and exhibited greater number of wet-dog shakes than controls. Although the AD threshold was not different between control and experimental rats, the above results seem to indicate an increase in the local epileptic susceptibility represented by longer ADs. On the other hand, this increased local discharge seems to be unable to access the generalization mechanism, which can be verified by the increased kindling rate. Hyperosmolarity, pH alterations, or other generalized metabolic changes frequently associated with diabetes could be implicated in these results.

Hypercalcemic effect of insulin in thyroparathyroidectomized alloxan-treated rats.

The acute effect of a hypoglycaemic dose of 0.5 U/100 g BW insulin administered intramuscularly on calcium metabolism was investigated in fasted alloxan-treated rats. It was found that the hypercalcaemic effect of insulin was evident only in thyroparathyroidectomized (TPTX) and not in parathyroidectomized (PTX) rats. A subcutaneous administration of 180 MRC mU/100 g BW calcitonin abolished the calcium raising effect of insulin in TPTX rats suggesting a protective role of calcitonin against insulin action in intact rats. In an attempt to elucidate the mechanism of the calcium raising effect of insulin 45Ca administered intravenously was used to indicate the movement of calcium from the plasma pool. Insulin administration delayed the plasma 45Ca disappearance rate but had no effect on bone 45Ca uptake within 120 min. In contrast, insulin administration resulted in a 31% reduction of urinary 45Ca excretion while the urine volume remained unchanged. However, the insulin-induced reduction of urinary calcium excretion could not totally account for the calcium raising effect of insulin in TPTX animals.

Influence of streptozotocin- and alloxan-induced diabetes on the metabolism of glycosaminoglycans

GAG metabolism was investigated in rats with experimentally induced diabetes. In comparison to control animals, the uptake of 35S-sulfate was diminished in tissues of diabetic animals. Streptozotocin-induced diabetes showed a significant decrease in the content of GAG fractions except that of non-sulfated GAG in liver and kidney which was unchanged as compared to the control group. In rats rendered diabetic by alloxan, non-sulfated GAG increased appreciably in liver and kidney whereas highly sulfated GAG remained unchanged. In the skins of alloxan-diabetic rats both total and sulfated GAG decreased significantly. The activities of liver beta-glucuronidase, beta-N-acetyl glucosaminidase and cathepsin D were significantly increased in rats treated with streptozotocin and alloxan. In streptozotocin-diabetic rats, renal beta-glucuronidase and beta-N-acetyl glucosaminidase activities were reduced while cathepsin D activity was similar to that of controls. The renal beta-N-acetyl glucosaminidase and cathepsin D activities of alloxan-treated rats were not significantly different from normal but their beta-glucuronidase was significantly increased. In the spleen of streptozotocin-diabetic rats all the enzymes were increased except beta-N-acetyl glucosaminidase which remained unaltered. Increased excretion of uronic acid was observed in diabetic groups. These results collectively indicate that both streptozotocin- and alloxan-induced diabetes altered the synthesis and catabolism of GAG.

The effect of alloxan, and alloxan-induced diabetes on the kidney.

Alloxan is known to induce diabetic renal changes as well as causing nephrotoxic alterations. However, no ultrastructural study has been performed to differentiate diabetic verses toxic affects of alloxan to the tubule and/or glomerulus. Therefore the present study used the "protected" kidney model to prevent one kidney from being exposed to the alloxan while allowing the other to receive the drug immediately. In all experimental animals the right renal hilum was gently occluded for 5 minutes and then released. This was performed prior to the injection of alloxan. Subsequently, the left renal hilum was occluded at the time of, and for 5 minutes after, alloxan administration (40 mg/kg i.v.). The experimental rats were divided into three groups: untreated diabetics, diabetics treated with protamine-zinc-insulin, and alloxan-treated rats that failed to become diabetic. Three groups of controls were included: one group received an equal volume of saline diluent as the experimental rats but no clamping of either renal hilum; another group received the saline and had the left renal hilum occluded for 5 minutes; and a third group had both the right and left renal hila occluded. All animals were followed and sacrificed after 9 weeks. Endogenous creatinine clearance did not change among groups. Alloxan-treated nondiabetic rats displayed marked interstitial nephritis in unprotected kidneys, while protected kidneys were normal. The diabetic state resulted in mesangial proliferation and focal glomerular basement membrane thickening as well as glomerular capillary endothelial abnormalities and visceral epithelial foot-process fusion. The endothelial changes consisted of focal areas showing a reduction in the size of endothelial fenestrae. All glomerular changes were ameliorated by insulin treatment. We conclude: 1) alloxan per se is distinctly nephrotoxic; and 2) the glomerular endothelium and epithelium are involved early in the course of experimental diabetes.

Ganglioside treatment of genetic and alloxan-induced diabetic neuropathy.

Peripheral neuropathy is a common complication of diabetes. Using the mutant diabetic mouse C57BL/ks (db/db) and alloxan-treated rats, 30 days after intoxication, we investigated development and treatment with gangliosides of such a disease. The db/db mouse develops a neuropathy characterized by a loss in conduction velocity shown as early as 80-90 days after birth and maintained throughout life. At later stages (5-6 months of age) there is a drop in slow transport and myelin particle density. These changes are correlated by a lack of response to insulin treatment, which, prior to this stage, is capable of improving nerve conduction velocity (NCV). On the other hand gangliosides became effective, improving NCV, myelin particle density and sensory perception (auditory deficit) at 5 months of age in the db/db mouse. We presume that this differential neuronal response to insulin and gangliosides indicates a change of the neuropathy from a metabolic stage to neuronal. Alloxan induced diabetic neuropathy is treatable with gangliosides even 30 days after intoxication.

Fasting portal vein plasma levels of gastric inhibitory polypeptide (GIP) and extractable fasting GIP in the duodenal wall in rats treated with methylprednisolone or alloxan compared with normal controls.

Ten rats were treated with methylprednisolone, another 10 rats with alloxan, and a final 10 control rats with saline. Compared with the controls, the methyl-prednisolone-treated rats had increased fasting levels of serum insulin, blood glucose, and plasma GIP; the alloxan-treated rats had decreased fasting levels of insulin and increased levels of fasting blood glucose and plasma GIP. After removal of the duodenum in the fasting state, the amount of GIP was measured in duodenal tissue specimens after extraction with ice-cold acetic acid, pH 3.0, and with neutralized acetic acid at 95 C. The duodenal content of GIP was 765.5 +/- 60.2 ng/g in the methylprednisolone-treated rats, 897.6 +/-37.3 ng/g in the alloxan-treated rats, and 923.1 +/- 72.9 ng/g in the saline-treated control rats. There were no significant differences in duodenal GIP content between the various groups, nor did the fasting plasma GIP and the amount of duodenal GIP in the individual rats correlate significantly (r=0.147, p less than 0.1). The elevated levels of fasting plasma GIP in the diabetic rats treated with methylprednisolone or alloxan may be due to factors regulating the secretion of GIP rather than to changes in the duodenal content of GIP.

Augmented release of gastric inhibitory polypeptide into the portal vein in response to intraduodenal glucose and amino acids in anesthetized rats treated with methylprednisolone or alloxan.

Thirty rats were treated with methylprednisolone, 30 rats were treated with alloxan, and 30 control rats were treated with saline alone. The levels of fasting serum insulin and blood glucose and of plasma GIP before and after duodenal instillation of glucose or amino acids were measured using an acute rat preparation that enabled multiple blood samplings from the portal vein. Treatment of the rats with methylprednisolone was followed by increased fasting levels of serum insulin, blood glucose, and plasma GIP and by an augmented GIP release in response to duodenal glucose and amino acids as compared with normal controls. Similarly, treatment with alloxan was followed by decreased fasting levels of serum insulin, by increased fasting levels of blood glucose and plasma GIP, and by an increased GIP release in response to duodenal glucose and amino acids. The augmented GIP release in response to duodenal instillation of glucose and amino acids both in methylprednisolone-treated rats and in alloxan-treated rats may be explained by an increased absorption of these nutrients owing to an increased Na+ K+ ATPase activity in the intestinal mucosa of corticosteroid- and alloxan-treated rats. The elevated fasting GIP levels, on the other hand, are difficult to explain.