Protective role of D-saccharic acid-1,4-lactone in alloxan induced oxidative stress in the spleen tissue of diabetic rats is mediated by suppressing mitochondria dependent apoptotic pathway

The present study investigated the role of D-saccharic acid 1,4-lactone (DSL) in the spleen tissue of alloxan (ALX) induced diabetic rats. Diabetes was induced in rats by injecting ALX (at a dose of 120 mg/kg body weight) intraperitoneally in sterile normal saline. Elevated levels of blood glucose, glycosylated Hb and TNFα decreased levels of plasma insulin and disturbed intra-cellular antioxidant machineries were detected in ALX exposed animals. Oral administration of DSL at a dose of 80 mg/kg body weight, however, restored these alterations in diabetic rats. Studies on the mechanism of ALX-induced diabetes showed that hyperglycemia caused disruption of mitochondrial membrane potential in the spleen, released cytochrome C in the cytosol, activated caspase 3 and ultimately led to apoptotic cell death. Results suggest that DSL possesses the ability of protecting the spleen tissue from ALX-induced hyperglycemia and thus could act as an anti-diabetic agent in lessening diabetes associated spleen dysfunction.     

Protective role of D-saccharic acid-1,4-lactone in alloxan induced oxidative stress in the spleen tissue of diabetic rats is mediated by suppressing mitochondria dependent apoptotic pathway

The present study investigated the role of D-saccharic acid 1,4-lactone (DSL) in the spleen tissue of alloxan (ALX) induced diabetic rats. Diabetes was induced in rats by injecting ALX (at a dose of 120 mg/kg body weight) intraperitoneally in sterile normal saline. Elevated levels of blood glucose, glycosylated Hb and TNFα decreased levels of plasma insulin and disturbed intra-cellular antioxidant machineries were detected in ALX exposed animals. Oral administration of DSL at a dose of 80 mg/kg body weight, however, restored these alterations in diabetic rats. Studies on the mechanism of ALX-induced diabetes showed that hyperglycemia caused disruption of mitochondrial membrane potential in the spleen, released cytochrome C in the cytosol, activated caspase 3 and ultimately led to apoptotic cell death. Results suggest that DSL possesses the ability of protecting the spleen tissue from ALX-induced hyperglycemia and thus could act as an anti-diabetic agent in lessening diabetes associated spleen dysfunction.     

Hyperglycemia does not increase basal hypothalamo-pituitary-adrenal activity in diabetes but it does impair the HPA response to insulin-induced hypoglycemia

Recently, we established that hypothalamo-pituitary-adrenal (HPA) and counterregulatory responses to insulin-induced hypoglycemia were impaired in uncontrolled streptozotocin (STZ)-diabetic (65 mg/kg) rats and insulin treatment restored most of these responses. In the current study, we used phloridzin to determine whether the restoration of blood glucose alone was sufficient to normalize HPA function in diabetes. Normal, diabetic, insulin-treated, and phloridzin-treated diabetic rats were either killed after 8 days or subjected to a hypoglycemic (40 mg/dl) glucose clamp. Basal: Elevated basal ACTH and corticosterone in STZ rats were normalized with insulin but not phloridzin. Increases in hypothalamic corticotrophin-releasing hormone (CRH) and inhibitory hippocampal mineralocorticoid receptor (MR) mRNA with STZ diabetes were not restored with either insulin or phloridzin treatments. Hypoglycemia: In response to hypoglycemia, rises in plasma ACTH and corticosterone were significantly lower in diabetic rats compared with controls. Insulin and phloridzin restored both ACTH and corticosterone responses in diabetic animals. Hypothalamic CRH mRNA and pituitary pro-opiomelanocortin mRNA expression increased following 2 h of hypoglycemia in normal, insulin-treated, and phloridzin-treated diabetic rats but not in untreated diabetic rats. Arginine vasopressin mRNA was unaltered by hypoglycemia in all groups. Interestingly, hypoglycemia decreased hippocampal MR mRNA in control, insulin-, and phloridzin-treated diabetic rats but not uncontrolled diabetic rats, whereas glucocorticoid receptor mRNA was not altered by hypoglycemia. In conclusion, despite elevated basal HPA activity, HPA responses to hypoglycemia were markedly reduced in uncontrolled diabetes. We speculate that defects in the CRH response may be related to a defective MR response. It is intriguing that phloridzin did not restore basal HPA activity but it restored the HPA response to hypoglycemia, suggesting that defects in basal HPA function in diabetes are due to insulin deficiency, but impaired responsiveness to hypoglycemia appears to stem from chronic hyperglycemia.     

Altered tail-skin temperature responsiveness in streptozotocin-induced diabetic rats

We evaluated the tail-skin temperature response to administration of several doses of isoproterenol in streptozotocin-induced diabetic rats after 48 h and after 4 weeks of diabetes. Blood glucose concentrations were significantly increased over controls 48 hours after administration of streptozotocin (65 mg/kg, i.v.) and remained elevated to a similar degree in the 4-week group. Basal rectal temperature and tail-skin temperature (TST) were not different between controls and the diabetic groups and were not affected by administration of saline. However, administration of isoproterenol (25 micrograms/kg, s.c.) caused a significant rise in TST in the control group, but not in the rats diabetic for 4 weeks. A similar but exaggerated response was observed in the controls after subcutaneous administration of 40 micrograms/kg and 100 micrograms/kg of isoproterenol. The TST response in the 4-week diabetic rats still remained negligible with the two higher doses of isoproterenol. When the data were summarized as area under the TST curve, a dose-dependent increase was observed in the control groups and a significant absence of response was observed in the 4-week group. The rats studied 48 h after streptozotocin injection had a similar TST response to the control group after administration of 40 micrograms/kg of isoproterenol. Colonic temperatures did not significantly change between the two groups in any of the studies, although the colonic temperatures tended to rise in the control groups following administration of isoproterenol. We conclude from this study that the absence of a tail-skin temperature response in rats diabetic for 4 weeks results from either a reduced beta-adrenergic receptor mediated response or an altered neural thermoregulatory reflex response, or both. These changes are probably not due to streptozotocin treatment or increases in blood glucose.     

Chronotropic function in spontaneously diabetic BB rats

In the present study, isolated atrial function in spontaneously diabetic BB Wistar rats maintained for 12 weeks on a low (BB-LI) and a high (BB-HI) dosage of insulin was examined. Basal atrial rates were unchanged in the diabetic animals, relative to nondiabetic littermates (ND-BB) or Wistar controls. The BB-HI animals were euglycemic and responded to isoproterenol in a similar manner to the ND-BB and Wistar control animals. In contrast, BB-LI animals remained hyperglycemic and exhibited lower responses to the maximum chronotropic effects of isoproterenol. Plasma thyroid hormone levels were unaltered in the BB-diabetic animals. These results therefore reveal an absence of bradycardia and hypothyroidism in spontaneously diabetic BB rats, in contrast to previous observations in streptozotocin diabetic rats. However, a decrease in chronotropic response to isoproterenol was still noted in the BB-LI animals. These findings suggest that decreased positive chronotropic effect of isoproterenol in diabetes may not be a direct consequence of altered thyroid status.     

Diabetes induces pulmonary artery endothelial dysfunction by NADPH oxidase induction

Recent data suggest that diabetes is a risk factor for pulmonary hypertension. The aim of the present study was to analyze whether diabetes induces endothelial dysfunction in pulmonary arteries and the mechanisms involved. Male Sprague-Dawley rats were randomly divided into a control (saline) and a diabetic group (70 mg/kg(-1) streptozotocin). After 6 wk, intrapulmonary arteries were mounted for isometric tension recording, and endothelial function was tested by the relaxant response to acetylcholine. Protein expression and localization were measured by Western blot and immunohistochemistry and superoxide production by dihydroethidium staining. Pulmonary arteries from diabetic rats showed impaired relaxant response to acetylcholine and reduced vasoconstrictor response to the nitric oxide (NO) synthase inhibitor L-NAME, whereas the response to nitroprusside and the expression of endothelial NO synthase remained unchanged. Endothelial dysfunction was reversed by addition of superoxide dismutase or the NADPH oxidase inhibitor apocynin. An increase in superoxide production and increased expression of the NADPH oxidase regulatory subunit p47(phox) were also found in pulmonary arteries from diabetic rats. In conclusion, the pulmonary circulation is a target for diabetes-induced endothelial dysfunction via enhanced NADPH oxidase-derived superoxide production.     

Rates and tissue sites of noninsulin- and insulin-mediated glucose uptake in diabetic rats.

The purpose of the present study was to determine whether streptozotocin-induced diabetes alters the rates and tissue distribution of insulin-mediated glucose uptake (IMGU) and noninsulin-mediated glucose uptake (NIMGU). In vivo glucose disposal was assessed using the tracer [U-14C]-2-deoxyglucose technique in chronically catheterized conscious rats. For nondiabetic animals, rates of NIMGU were determined during severe insulinopenia (less than 5 microU/ml), induced by the infusion of somatostatin, under both euglycemic (6 mM) and hyperglycemic (17 mM) conditions. In diabetic rats, in which a severe insulin deficiency already existed, NIMGU was determined under basal hyperglycemic conditions and during euglycemic conditions produced by inhibiting hepatic glucose output. IMGU was determined in both groups using the euglycemichyperinsulinemic clamp technique. Glucose uptake was consistently higher (50-280%) in all tissues removed from diabetic rats under basal conditions, compared with tissues from control animals in the basal state. When control animals were rendered insulinopenic, glucose uptake by the skeletal muscle, heart, and diaphragm was reduced 30-60%, indicating that the uptake by these tissues occurred by both insulin- and noninsulin-mediated mechanisms. Glucose disposal by the other tissues sampled was entirely due to NIMGU under basal conditions. When blood glucose levels were elevated from 6 to 17 mM in control animals, NIMGU increased in all tissues (60-280%) except the brain. Rates of NIMGU were essentially identical between control and diabetic animals, under either euglycemic or hyperglycemic conditions, when glucose uptake was determined under the same steady-state plasma glucose levels. In contrast to the normal rate of NIMGU by muscle, IMGU by the skeletal muscle and heart from diabetic rats were reduced under mild hyperinsulinemic conditions (100 microU/ml), compared with control animals. Furthermore, in response to a maximal, stimulating dose of insulin (500 microU/ml), IMGU was impaired in the diaphragm, liver, lung, spleen, skin, and kidney removed from diabetic animals. These results indicate that the majority of glucose disposal under basal postabsorptive conditions occurs by NIMGU in both control and diabetic rats. Furthermore, while IMGU was selectively impaired in this model of insulin-dependent diabetes, the rates and tissue distribution of NIMGU were unaltered when glucose uptake was determined under similar plasma glucose levels.     

Ovarian dysfunction in streptozotocin-induced diabetic rats

The effect of streptozotocin diabetes on some ovarian functions in adult rats was examined. Diabetic diestrus animals showed reduced ovary weight and lower circulating levels of progesterone. Scatchard plots of binding data derived from ovarian particulate fractions of normal and streptozotocin diabetic rats revealed the presence of one class of binding sites with high affinity for 125I-hCG. The apparent association constant of the hCG receptors of diabetic ovaries was comparable to that of normal gonads. However, a marked decrease (42%) in the number of hCG binding sites was found in diabetic animals. With isolated luteal cells similar results were obtained, and the administration of insulin to streptozotocin diabetic rats restored to normality the number of hCG binding sites. The maximal response of progesterone production by luteal cells from control ovaries was obtained with 10(-10) M hCG. A 100-fold higher concentration of hCG was required for the maximum stimulation of cAMP synthesis. The cAMP response of cells from diabetic rats was significantly higher than that of control cells. However, luteal cells from diabetic rats showed some loss of sensitivity in the synthesis of progesterone during incubation with hCG. Most of the alterations seen in diabetic female rats could be restored with insulin therapy, indicating that insulin plays an important role in the regulation and maintenance of normal reproductive functions. It is suggested that the diminution of the LH receptor population causes the disruption of normal luteal cell function. This fact could be responsible for some of the reproductive alterations in the diabetic female rat.     

Low-carbohydrate diet and oxidative stress in diabetic and nondiabetic rats

Hyperglycemia of diabetes has been implicated in increased tissue oxidative stress, with consequent development of secondary complications. Thus, stabilizing glucose levels near normal levels is of utmost importance. Because diet influences glycemic control, this study investigated whether a low-carbohydrate (5.5%) diet confers beneficial effects on the oxidative status of the heart, kidney, and liver in diabetes. Male and female normal and diabetic rats were fed standard chow (63% carbohydrates) or low-carbohydrate diet for 30 days. Elevated glucose, HbA(1c), and alanine and aspartate aminotransferases in diabetic animals were reduced or normalized by the low-carbohydrate diet. While diabetes increased cardiac activities of glutathione peroxidase and catalase, low-carbohydrate diet normalized cardiac glutathione peroxidase activity in diabetic animals, and reduced catalase activity in females. Diabetic rats fed low-carbohydrate diet had altered activities of renal glutathione reductase and superoxide dismutase, but increased renal glutathione peroxidase activity in diabetic animals was not corrected by the test diet. In the liver, diabetes was associated with a decrease in catalase activity and glutathione levels and an increase in glutathione peroxidase and gamma-glutamyltranspeptidase activities. Decreased hepatic glutathione peroxidase activity and lipid peroxidation were noted in diet-treated diabetic rats. Overall, the low-carbohydrate diet helped stabilize hyperglycemia and did not produce overtly negative effects in tissues of normal or diabetic rats.     

Antioxidant enzyme alterations in experimental and clinical diabetes

Previous studies from our laboratory have demonstrated the presence of complex alterations in the activities of antioxidant enzymes in various tissues of rats with streptozotocin (STZ)-induced diabetes. In the present investigation, it is shown that rats made diabetic with alloxan (ALX), an agent differing from STZ both chemically and in its mechanism of diabetogenesis, show virtually identical tissue antioxidant enzyme changes which, as is the case with STZ, are preventable by insulin treatment. The finding that the patterns of antioxidant enzyme alterations in chemically-induced diabetes are independent of the diabetogenic agent used and the presence of similar abnormalities in tissues of spontaneously diabetic (BB) Wistar rats (particularly when diabetic control is less than optimal) suggest that the changes observed are a characteristic feature of the uncontrolled diabetic state and that these may be responsible for (or predispose to) the development of secondary complications in clinical diabetes. Comparative studies involving red cells of diabetic rats and human diabetics revealed a number of common changes, namely an increase in glutathione reductase activity, a decreased susceptibility to oxidative glutathione depletion (which was related to the presence of hyperglycemia) and an increased production of malondialdehyde (an indirect index of lipid peroxidation) in response to in vitro challenge with hydrogen peroxide. In the diabetic patients, the extent of this increase in susceptibility of red cell lipids to oxidation paralleled the severity of diabetic complications. Our results suggest that increased (or uncontrolled) oxidative activity may play an important role in the pathogenesis of complications associated with the chronic diabetic state.This work was supported by grants from the British Columbia Health Care Research Foundation and the Canadian Diabetes Association.     

Co-administration of dopamine D1 and D2 agonists additively decreases daily food intake, body weight and hypothalamic neuropeptide Y level in rats

This study investigated whether co-administration of dopamine D1 and D2 agonists might additively inhibit the feeding effect and whether this effect was mediated by the action on hypothalamic neuropeptide Y (NPY). The D1 agonist SKF 38393 (SKF) and D2 agonists apomorphine (APO) or quinpirole (QNP) were administered, alone or in combination, to examine this possibility. In single administration, decreases of daily food intake were observed only in rats treated twice a day with a higher dose of SKF, APO or QNP. However, combined administration of D1 and D2 agonists, with each agent at a dose that alone did not induce anorexia in one daily treatment, exerted a significant effect. These results reveal that co-activation of D1 and D2 receptors can additively reduce daily food intake and body weight. The same treatment also decreased the level of hypothalamic NPY 24 h post-treatment. These results suggest an additive effect during combined activation of D1 and D2 receptor subtypes to decrease food intake and body weight that are mediated by the action of hypothalamic NPY. Similar to the effects seen in healthy rats, combined D1/D2 administration was also effective in the reduction of food intake in diabetic rats, revealing the efficiency of D1/D2 agonist in the improvement of hyperphasia in diabetic animals.     

Does estradiol treatment normalize the hypothalamic-pituitary-adrenal axis in streptozotocin-induced ovariectomized diabetic female rats?

We recently found circulating corticosterone (CS) levels to be significantly lower in diabetic female rats as compared with proestrous control animals. This reduction in CS was correlated with the hypoestrogenic state of the diabetic female. It was the purpose of this study to evaluate basal and corticotropin releasing hormone (CRH)-stimulated CS secretion in ovariectomized (OVX) control (C) and streptozotocin-induced diabetic (D) rats given blank, 5 mcg and 20 mcg estradiol (E2) implants to determine if adrenal CS secretion in the diabetic is normalized by E2 treatment. After 3 weeks of diabetes, pituitary-adrenal function was assessed in rats from each group with a CRH stimulation test. The remaining rats were sacrificed for determination of CS, E2, testosterone and fructosamine in serum. Suppressed CS secretion in OVX female diabetic rats was partially restored with E2 therapy. Basal CS levels were significantly higher in 20 mcg E2 treated C and D rats compared with OVX rats. However, C rats had significantly higher basal CS compared with D rats in similarly E2 treated groups. The CS response to CRH stimulation was not different between OVX female diabetic and control rats. Estrogen enhanced the CS response to CRH stimulation in control animals but not in diabetic animals suggesting altered estrogen action at the pituitary level in diabetic animals.     

Effects of a selective endothelin a receptor antagonist on the expressions of iNOS and eNOS in the heart of early streptozotocin-induced diabetic rats

Vascular tone is regulated through the actions of locally produced agents. Among the vasoconstrictors, the most potent agent is endothelin (ET), which exerts its vasoconstrictor actions principally through ET type A (ET(A)) receptors. Of the vasodilators, nitric oxide (NO) seems to be the most important contributor to the acute regulation of vascular tone. Vasculopathy is an important feature of diabetes mellitus (DM). Endogenous ET-mediated vasoconstrictor tone is augmented in diabetic states, and conflicting results persist concerning the NO system in diabetes. The present study investigated the expressions of inducible NO synthases (iNOS) and endothelial NOS (eNOS) in the heart of diabetic animals and the effects of a selective ET(A) receptor antagonist on these alterations. Type I diabetes was induced by intraperitoneal injection of streptozotocin (65 mg/kg) in Sprague-Dawley rats, while control (Con) rats received only citrate buffer. After 1 week, the streptozotocin-administered rats were randomly divided into two groups: the selective ET(A) receptor antagonist-administered group (DM+TA-0201, 1 mg/kg/day, by osmotic minipump for 2 weeks) and the DM+vehicle group (comprising the diabetic rats that received saline). The random blood glucose level was 405 +/- 103 mg/dl in DM animals, and this level was unchanged by ET antagonism. Body weight was more greatly decreased in DM rats than in Con rats, but the left ventricle to body weight ratio was increased in the DM group and was unaffected by ET antagonism. Protein expressions of eNOS and iNOS were assessed in the left ventricular tissues. eNOS expression was significantly increased in DM heart and was greatly inhibited by the treatment with ET antagonist. The expression of iNOS was also increased in early DM heart but was reversed by the ET antagonist. Thus, endothelin antagonism might be beneficial for DM heart by reversing the upregulated eNOS and iNOS expressions.     

Influence of exercise on dilatation of the basilar artery during diabetes mellitus.

Our goal was to examine whether exercise training alleviates impaired nitric oxide synthase (NOS)-dependent dilatation of the basilar artery in Type 1 diabetic rats. To test this hypothesis, we measured in vivo diameter of the basilar artery in sedentary and exercised nondiabetic and diabetic rats in response to NOS-dependent (acetylcholine) and -independent (nitroglycerin) agonists. To determine the potential role for nitric oxide in vasodilatation in sedentary and exercised nondiabetic and diabetic rats, we examined responses after NG-monomethyl-l-arginine (l-NMMA). We found that acetylcholine produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic rats. Acetylcholine produced only minimal vasodilatation in sedentary diabetic rats. However, exercise alleviated impaired acetylcholine-induced vasodilatation in diabetic rats. Nitroglycerin produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic and diabetic rats. l-NMMA produced similar inhibition of acetylcholine-induced dilatation of the basilar artery in sedentary and exercised nondiabetic and diabetic rats. Finally, we found that endothelial NOS (eNOS) protein in the basilar artery was higher in diabetic compared with nondiabetic rats and that exercise increased eNOS protein in the basilar artery of nondiabetic and diabetic rats. We conclude that 1) exercise can alleviate impaired NOS-dependent dilatation of the basilar artery during diabetes mellitus, 2) the synthesis and release of nitric oxide accounts for dilatation of the basilar artery to acetylcholine in sedentary and exercised nondiabetic and diabetic rats, and 3) exercise may exert its affect on cerebrovascular reactivity during diabetes by altering levels of eNOS protein in the basilar artery.     

Cold-acclimation improves cold-tolerance of diabetic rats

1. The aim of these experiments was to study the extent to which previous cold-acclimation improves the cold-tolerance of diabetic rats. 2. Alloxan diabetic rats (fasting blood glucose higher than 200 mg/dl) were used in the experiments. 3. In Expt. 1, non-cold-acclimated control and diabetic rats were exposed to cold environment (7-9 degrees C), and the percentage of survival calculated during a 12-day experimental period. In Expt. 2, the rats were previously cold-acclimated before alloxan or saline injection (diabetic and control cold-acclimated rats) and the survival rate was also assessed during a 12-day period in the cold. 4. The percentage of survival of the non-cold-acclimated diabetic rats (Expt.1) was 19% compared with 79% of the diabetic cold-acclimated animals (Expt. 2). There were no deaths in the control groups. 5. Cold-acclimated diabetic rats maintained a near-normal thermogenic response after noradrenaline injection. This response was impaired in non-cold-acclimated diabetic rats. 6. The results of these experiments suggest that the enhanced cold-tolerance of diabetic cold-acclimated rats could be related to the increased sympathetic activity and enhanced insulin sensitivity in thermogenic tissues, such as brown fat.     

Enalapril treatment corrects the reduced response to bradykinin in diabetes increasing the B2 protein expression

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the effect of enalapril on the reduced response of bradykinin and on the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems, in an insulin-resistance model of diabetes. For the above purpose, the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. In n-STZ diabetic rats, enalapril treatment restored the reduced response to BK but not the potentiation of BK by Ang-(1-7) present in non-diabetic rats. The restorative effect of enalapril was observed at a dose that did not correct the altered parameters induced by diabetes such as hyperglycemia, glicosuria, insulin resistance but did reduce the high blood pressure levels of n-SZT diabetic rats. There was no difference in mRNA and protein expressions of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Enalapril treatment increased the B2 kinin receptor expression. From our data, we conclude that in diabetes enalapril corrects the impaired BK response probably by increasing the expression of B2 receptors. The lack of potentiation of BK by Ang-(1-7) is not corrected by this agent.     

Antithrombotic effect of onion in streptozotocin-induced diabetic rat

In the present study, we investigated whether onion has antithrombotic effect in streptozotocin (STZ)-induced diabetic rats. In diabetic rats, serum thromboxane B(2) (TXB(2)) level was elevated compared to that in normal, and this elevation in diabetes was significantly inhibited by treatment with onion (0.5 g/ml/kg/day, i.p.) for 4 weeks. In normal rats, the serum TXB(2) level remained unaltered after the treatment with onion. To investigate in vitro effect of onion, we examined its effect on TXB(2) formation, platelet aggregation and arachidonic acid (AA)-release in platelets from diabetic and normal rats. Onion showed a significant inhibitory effect on collagen- or AA-induced TXB(2) formation with greater potency in diabetic platelets than in normal. Similarly, more potent inhibitory effects of onion in diabetes were observed in collagen- or AA-induced platelet aggregation and collagen-induced AA release response. In conclusion, these results suggest that onion can produce more beneficial antithrombotic effect in diabetes.     

Molecular target structures in alloxan-induced diabetes in mice

Type 1 diabetes results from irreversible damage of insulin-producing beta-cells. In laboratory animals, diabetes can be induced with alloxan (ALX), a 2,4,5,6-tetraoxopyrimidine. ALX is a potent generator of reactive oxygen species (ROS), which can mediate beta-cell toxicity. However, the initial lesions on essential beta-cell structures are not known. In this study, we report that the glucose transporter 2 (GLUT2) and glucokinase (GK) are target molecules for ALX. Ex vivo, a gradual decrement of both GLUT2 and GK mRNA expression was found in islets isolated from ALX-treated C57BL/6 mice. This reduction was more pronounced for GLUT2 than for GK. The mRNA expression of beta-actin was also slightly affected with time after ALX exposure, the proinsulin mRNA, however, remained unaffected as well as the pancreatic total insulin content. Pretreatment with D-glucose (D-G) protected the mRNA expression of GLUT2 and GK against ALX toxicity and prevented diabetes. Yet, in these euglycemic mice, an impaired oral glucose tolerance persisted. Pretreatment with 5-thio-D-glucose (5-T-G) failed to prevent ALX diabetes, administration of zinc sulfate (Zn(2+))-enriched drinking water, however, reduced ALX-induced hyperglycemia. In conclusion, ALX exerted differential toxicity on beta-cell structures similar to in vitro results reported from this laboratory. Furthermore, the present results differ from those reported for the diabetogen streptozotocin (STZ). Injections of multiple low doses (MLD) of STZ reduced GLUT2 expression only, but failed to affect expression of GK and proinsulin as well as beta-actin as internal control. MLD-STZ diabetes was prevented by pretreatment with both D-G and 5-T-G and administration of Zn(2+)-enriched drinking water. Apparently, ALX and MLD-STZ exert diabetogenicity by different pathways requiring different interventional schedules for prevention.     

Alterations in vascular endothelial function in the aorta and mesenteric artery in type II diabetic rats

We used the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create an experimental diabetic syndrome in adult rats that appears closer to type II diabetes mellitus than other available animal models. The dosage of 230 mg/kg of nicotinamide given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded animals with hyperglycemia (187.8 +/- 17.8 vs. 103.8 +/- 2.8 mg/dL in controls; P < 0.001) and preservation of plasma insulin levels. This study assessed the relationship between endothelial dysfunction and agonist-induced contractile responses in such rats. In the thoracic aorta, the acetylcholine (ACh) induced relaxation was significantly reduced and the noradrenaline (NA) induced contractile response was significantly increased in diabetic rats compared with age-matched control rats. In the superior mesenteric artery, the ACh-induced relaxation was similar in magnitude between diabetic and age-matched control rats; however, the ACh-induced endothelium-derived hyperpolarizing factor (EDHF) type relaxation was significantly weaker in diabetic rats than in the controls. The phenylephrine (PE) induced contractile response was not different between the two groups. The plasma concentration of NOx (NO2- + NO3-) was significantly lower in diabetic rats than in control rats. We conclude that vasomotor activities in conduit arteries are impaired in this type II diabetes model.