Regulation of hepatic glutaminase in the streptozotocin-induced diabetic rat

The liver of diabetic animals removes increased quantities of glutamine. We therefore examined factors that affect hepatic glutaminase activity in hepatocytes and mitochondria. Glutamine use, through glutaminase, was measured in isolated rat hepatocytes by monitoring the production of 14CO2 from [1-(14)C]glutamine. Hepatocytes from streptozotocin-induced diabetic rats use glutamine more rapidly than do hepatocytes from normal or insulin-maintained diabetic rats. Glutamine use in all of these hepatocytes was stimulated by glucagon and epinephrine. Glutaminase activity, assayed in broken mitochondrial membranes, was increased approximately 2.5-fold in diabetic rats. The sensitivity of glutaminase, measured in intact liver mitochondria, to phosphate was markedly left-shifted in mitochondria from diabetic rats compared with those from controls. In fact, glutaminase was increased 10-fold at 2.5 mmol/l phosphate compared with controls. This increased sensitivity of glutaminase to physiological concentrations of phosphate is characteristic of its hormonal activation. Therefore, activation of glutaminase plays a major role in diabetes and is as important as increases in its total enzyme amount in determining the increased glutamine uptake in diabetes.     

Enhanced hemodynamic response to [D-ALA2,D-MET5]-methionine enkephalin (DAME) in streptozotocin-induced diabetic rats is reversed by insulin replacement

The present study examined the alterations of hemodynamic responses to [D-ala2,D-Met5]-methionine enkephalin (DAME) in diabetic animals. Male Sprague-Dawley rats (12 weeks old) were used for this study. Diabetes was induced by a single injection of streptozotocin (65 mg/kg, i.v.). After 7 days, blood glucose levels were determined to confirm the diabetic state. Animals were anesthetized and instrumented to monitor mean arterial pressure, hindlimb bloodflow and hindlimb vascular resistance. Administration of DAME produced a significantly greater reduction in blood pressure, increase in hindlimb bloodflow and decrease in hindlimb vascular resistance in diabetic vs. control rats. These effects were blocked by naloxone. All hemodynamic changes were attenuated after pretreatment with the ganglionic blocker, hexamethonium, indicating that the responses were mediated either within the central nervous system or at the ganglia. Insulin reversed the exaggerated depressor effect of DAME on streptozotocin-treated rats. Collectively, these results suggest that diabetic rats have altered opioidergic hemodynamic responses to DAME due to mu receptor alterations in the CNS or in autonomic ganglia. These effects were reversed by replacement of insulin.     

Energy metabolism after ischemic preconditioning in streptozotocin-induced diabetic rat hearts

OBJECTIVES: The aim of this study was to compare the cardioprotective effects of preconditioning in hearts from streptozotocin-induced diabetic rats with its effects in normal rat hearts. BACKGROUND: The protective effect of ischemic preconditioning against myocardial ischemia may come from improved energy balance. However, it is not known whether preconditioning can also afford protection to diabetic hearts. METHODS: Isolated perfused rat hearts were either subjected (preconditioned group) or not subjected (control group) to preconditioning before 30 min of sustained ischemia and 30 min of reperfusion. Preconditioning was achieved with two cycles of 5 min of ischemia followed by 5 min of reperfusion. RESULTS: In the preconditioned groups of both normal and diabetic rats, left ventricular developed pressure, high energy phosphates, mitochondrial adenosine triphosphatase and adenine nucleotide translocase activities were significantly preserved after ischemia-reperfusion; cumulative creatine kinase release was smaller during reperfusion; and myocardial lactate content was significantly lower after sustained ischemia. However, cumulative creatine kinase release was less in the preconditioned group of diabetic rats than in the preconditioned group of normal rats. Under ischemic conditions, more glycolytic metabolites were produced in the diabetic rats (control group) than in the normal rats, and preconditioning inhibited these metabolic changes to a similar extent in both groups. CONCLUSIONS: The present study demonstrates that in both normal and diabetic rats, preservation of mitochondrial oxidative phosphorylation and inhibition of glycolysis during ischemia can contribute to preconditioning-induced cardioprotection. Furthermore, our data suggest that diabetic myocardium may benefit more from preconditioning than normal myocardium, possibly as a result of the reduced production of glycolytic metabolites during sustained ischemia and the concomitant attenuation of intracellular acidosis.     

Upregulation of osteopontin expression in renal cortex of streptozotocin-induced diabetic rats is mediated by bradykinin

The model of streptozotocin (STZ)-induced diabetes in Wistar rats was used to study the expression of osteopontin during development of diabetic nephropathy. Diabetes was confirmed by serum glucose levels exceeding 16 mmol/l during the experimental period of 12 weeks. During this period of time, diabetic nephropathy developed, as characterized by a reduced glomerular filtration rate (2.7 +/- 0.3 ml/min in controls vs. 1.7 +/- 0.1 ml/min in diabetic rats) and proteinuria (8.3 +/- 1.7 mg/24 h in controls vs. 22.0 +/- 4 mg/24 h in diabetic rats). Northern blot analysis revealed a time-dependent upregulation of renal cortical osteopontin expression reaching 138 +/- 6% of control levels after 2 weeks and 290 +/- 30% (mean +/- SE, n = 6-9) after 12 weeks. By immunostaining, the increased osteopontin expression could be located to the tubular epithelium of the renal cortex. Chronic treatment of animals with ramipril (3 mg/kg) during the 12-week experimental period led to a further increase in osteopontin mRNA expression in diabetic animals, amounting to 570 +/- 73% (mean +/- SE, n = 6) of controls. Increased levels of osteopontin were not associated with accumulation of monocyte/macrophages that were identified by the cell type specific monoclonal antibody ED-1. The increased osteopontin expression in ramipril-pretreated rats was abolished by application of the bradykinin B2-receptor antagonist, icatibant (0.5 mg/kg). In addition, increased osteopontin expression in diabetic rats, which did not receive any treatment after STZ injection, could as well be reduced by icatibant given for the final 2 weeks of the experimental period. These data suggest that a strong bradykinin B2-receptor-mediated upregulation of osteopontin occurs during the pathogenesis of experimental diabetic nephropathy in rats.     

Tolerance to IDDM induced by CD4 antibodies in nonobese diabetic mice is reversed by cyclophosphamide

IDDM can be induced in nonobese diabetic (NOD) mice in several ways, including high doses of cyclophosphamide and transfer of diabetic spleen cells to sublethally irradiated recipients. It has previously been established that transferred diabetes can be prevented by treatment with a nondepleting CD4 monoclonal antibody; however, we report herein that cyclophosphamide-induced diabetes also can be prevented using this antibody. The protection induced by CD4 monoclonal antibody to transferred diabetes is maintained for a long period after cessation of antibody treatment. However, cyclophosphamide can abrogate this induced tolerance and we report that this abrogation does not require new T-cells. During the course of the experimental work described, we observed that the thymus had a suppressive effect on the expression of transferred disease. Mice that were depleted of their peripheral T-cells showed a doubling of the time for disease expression if they were euthymic, compared with thymectomized mice.     

The effect of the sulfonylurea glyburide on nitric oxide in streptozotocin-induced diabetic rat

1. The interaction between nitric oxide (NO) and superoxide anions has received a great deal of attention. Because NO is rapidly inactivated by superoxide anions, it has been suggested that an enhanced formation of this radical may be involved in the accelerated breakdown of NO. 2. In the present study, we administrated glyburide (glibenclamide) to Streptozotocin-induced diabetic rats and determined the effect of such treatment on serum nitrite+nitrate levels. Serum nitrite+nitrate levels were reduced in diabetic animals (P<0.001). Administration of glyburide to diabetic rats reversed the diabetes-induced changes, suggesting that glyburide may directly increase serum nitrite+nitrate levels.     

Elevated plasma endothelin-1 level in streptozotocin-induced diabetic rats and responsiveness of the mesenteric arterial bed to endothelin-1

Acute swimming stress destroyed the circadian rhythm of motility in rats. Bilateral electrolytic lesion of the dorsal hippocampus increased the night activity and resistance of animals to stress. Pinealectomy did not affect the circadian locomotion but increased rats' sensitivity to dysrhythmic stress effect.     

Modulation of renal kallikrein production by dietary protein in streptozotocin-induced diabetic rats

Renal kallikrein levels and excretion rates are increased in insulin-treated diabetic rats with hyperfiltration, and inhibition of kallikrein or blockade of kinin receptors reduces GFR and RPF. In contrast, insulin-deprived severely (SD) diabetic rats that display renal vasoconstriction show reduced levels and excretion rates of renal kallikrein. In these two models, dietary protein manipulation was utilized to study further the relationships between renal kallikrein and renal hemodynamic regulation. Insulin-deprived SD and insulin-treated moderately diabetic (MD) rats were fed a low (9%), normal (25%), and a high (50%) protein diet. In SD rats fed the 50% protein diet, GFR, RPF, and kallikrein excretion rate were increased compared with SD rats fed the 25% protein diet (GFR, 2.66 +/- 0.16 versus 1.74 +/- 0.30 mL/min; RPF, 7.78 +/- 0.58 versus 5.14 +/- 1.03 mL/min; total kallikrein, 248 +/- 24 versus 120 +/- 30 micrograms/24 h, SD 50% versus SD 25%, respectively; P < 0.005). In MD rats fed the 9% protein diet, GFR, RPF, and kallikrein excretion rate were significantly reduced compared with MD 25% protein-fed rats (GFR, 1.54 +/- 0.07 versus 1.95 +/- 0.09 mL/min; RPF, 5.58 +/- 0.35 versus 7.81 +/- 0.35 mL/min; total kallikrein, 119 +/- 8.3 versus 219 +/- 15 micrograms/24 h, MD 9% versus MD 25%, respectively; P < 0.005). Protein restriction in normal nondiabetic rats resulted in a twofold decrease in kallikrein mRNA levels. These findings suggest that the renal hemodynamic response to dietary protein manipulation in diabetic rats could be mediated via changes in renal kallikrein-kinin system activity.     

Endothelial dysfunction and metabolic control in streptozotocin-induced diabetic rats

1. The aim of this work was to study the influence of the metabolic control, estimated by the levels of glycosylated haemoglobin in total blood samples (HbA1c), in developing vascular endothelial dysfunction in streptozotocin-induced diabetic rats. Four groups of animals with different levels of insulin treatment were established, by determining HbA1c values in 5.5 to 7.4%, 7.5 to 9.4%, 9.5 to 12% and > 12%, respectively. 2. The parameters analysed were: (1) the endothelium-dependent relaxations to acetylcholine (ACh) in isolated aorta and mesenteric microvessels; (2) the vasodilator responses to exogenous nitric oxide (NO) in aorta: and (3) the existence of oxidative stress by studying the influence of the free radical scavenger superoxide dismutase (SOD) on the vasodilator responses to both ACh and NO. 3. In both isolated aortic segments and mesenteric microvessels, the endothelium-mediated concentration-dependent relaxant responses elicited by ACh were significantly decreased when the vessels were obtained from diabetic animals but only with HbA1c values higher than 7.5%. There was a high correlation between HbA1c levels and the impairment of ACh-induced relaxations, measured by pD2 values. 4. The concentration-dependent vasorelaxant responses to NO in endothelium-denuded aortic segments were significantly reduced only in vessels from diabetic animals with HbA1c values higher than 7.5%. Again, a very high correlation was found between the HbA1c values and pD2 for NO-evoked responses. 5. In the presence of SOD, the responses to ACh or NO were only increased in the segments from diabetic rats with HbA1c levels higher than 7.5%, but not in those from non-diabetic or diabetic rats with a good metabolic control (HbA1c levels <7.5%). 6. These results suggest the existence of: (1) a close relation between the degree of endothelial dysfunction and the metabolic control of diabetes, estimated by the levels of HbA1c; and (2) an increased production of superoxide anions in the vascular wall of the diabetic rats, which is also related to the metabolic control of the disease.     

Captopril ameliorates the decreased Na+,K(+)-ATPase activity in the retina of streptozotocin-induced diabetic rats

PURPOSE: To examine the effect of captopril, an angiotensin-converting enzyme (ACE) inhibitor, on the activity of retinal sodium-potassium ATPase (Na,K-ATPase) and the activity of ACE in the serum and retina of streptozotocin (STZ)-induced diabetic rats. METHODS: Experimental diabetes was induced in male Long-Evans rats by a single intraperitoneal injection of STZ (55 mg/kg body weight). Some groups of normal and diabetic animals were treated with captopril (10 mg/kg per day) added to the drinking water for either a week or a month. After 2 and 4 months of diabetes, the specific activity of retinal total Na,K-ATPase was determined. The components of the activity of Na,K-ATPase caused by the alpha 1 and alpha 3 isoforms were pharmacologically separated by their different sensitivity to ouabain. The activity of ACE in the serum and retina was measured by radioassay using benzoyl-gly-gly-gly as substrate (10(5) cpm, 5 mM). RESULTS: The total Na,K-ATPase activity was decreased significantly after 2 (16%, P < 0.02) and 4 months (15%, P < 0.02) of diabetes. At both time points examined, the activities of the alpha 1-low-ouabain-affinity isoform and the alpha 3-high-ouabain-affinity isoform of retinal Na,K-ATPase were significantly reduced compared to those of age-matched controls (alpha 1, 9% to 14%, P < 0.05; alpha 3, 14% to 19%, P < 0.05 and P < 0.02 respectively). After 1 month of captopril administration, the activities of both Na,K-ATPase isoforms were at control level in 2-month diabetic rats, whereas they were restored only partially in 4-month diabetic rats. In age-matched normal animals, 1 month of captopril treatment did not alter the specific activities of either Na,K-ATPase isoform. One week or 1 month of captopril administration to diabetic rats did not change the activities of retinal Na,K-ATPase isoforms. Serum ACE activity was elevated significantly in both groups of untreated STZ rats (55% and 40%, respectively). One month of captopril administration further increased the ACE levels in 2- and 4-month diabetic rats (101% and 94%, respectively) and also enhanced significantly the serum ACE activity in normal animals (131%) versus the basal values. In contrast, retinal ACE activity was decreased significantly in both groups of untreated STZ rats (approximately 37%). Captopril exerted a significant inhibitory effect on the retinal ACE activity in 2- and 4-month diabetic rats (37% and 31%, respectively) compared to untreated diabetic animals as well as in normal rats (29%). CONCLUSIONS: These data suggest that stimulation of retinal Na,K-ATPase activity in diabetes is most likely one of the mechanisms through which captopril can improve retinal complications. The effect of captopril seems to be related to local effects in the retina. Whether the inhibition of retinal ACE is part of the mechanism of action of captopril requires further study.     

Salt appetite is enhanced by one prior episode of sodium depletion in the rat.

A single sodium depletion enhances the salt appetite that is expressed after a second and subsequent sodium depletions. The enhanced salt intake, as measured by a decrease in latency to drink and an increase in volume of 3% NaCl ingested, is not accounted for by an increased sodium loss. The enhanced salt intake occurs even when the interval between first and second depletion is as long as 4 months. The enhanced salt appetite does not depend on the drinking of salt after the animal's first sodium depletion and is specific for strong 0.52 M NaCl but not for 0.52 M KCl. Moreover, it can be produced without sodium depletion by the actions of the hormones aldosterone and angiotensin on the brain. These results suggest that angiotensin and aldosterone, which are released in response to sodium depletion, (a) increase renal sodium conservation, (b) evoke a salt appetite to restore the lost sodium, and (c) produce enduring changes in the brain that prepare it for more rapid and more vigorous expression of salt appetite in response to future sodium depletions. Thus the neural mechanisms that govern salt appetite are not only activated by the hormones of sodium conservation but appear also to be organized by them for a lifelong increase in avidity for salty substances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Improvement of impaired glucose tolerance by oral administration of vanadyl sulfate by gavage in streptozotocin-induced diabetic rats

We examined the effect of oral administration of vanadyl sulfate by gavage on the levels of blood glucose and plasma insulin during oral glucose tolerance test (OGTT) in diabetic rats. Diabetes was induced by intravenous injection of streptozotocin at the dose of 32 mg/kg. Nondiabetic control animals were injected with an equal volume of saline. Vanadyl sulfate at a dose of 25, 50, or 75 mg/kg was given orally by gavage for 2 weeks, starting 12 hours after streptozotocin injection. When vanadyl sulfate was given twice a day, half of the one-day-dosage was given in the morning and the remaining half in the evening. Glucose tolerance test with 5 g/kg of glucose was carried out 2 weeks after administration of vanadyl sulfate. The fasting the blood glucose level in the diabetic rats was higher than that in the non-diabetic rats, whereas the plasma insulin level in the diabetic rats was lower. An increase in blood glucose seen in the glucose tolerance test was significantly greater in the diabetic rats than in the non-diabetic rats. The level of plasma insulin was increased by glucose tolerance test in the non-diabetic rats, while it was not changed in diabetic rats. Oral administration of vanadyl sulfate by gavage significantly improved the impaired glucose tolerance in the the diabetic rats in a dose-dependent manner without any change in plasma insulin level. In conclusion, oral administration of vanadyl sulfate by gavage is effective on impaired glucose tolerance in streptozotocin-induced diabetic rats.     

Elevated interleukin-12 in progressive multiple sclerosis correlates with disease activity and is normalized by pulse cyclophosphamide therapy

The technique of pulse radiolysis has been used to investigate the possibility of intramolecular charge transfer in the dipeptide histidyltyrosine, following one-electron oxidation of one of its amino acid residues. The radical anion, Br2.- was found to react with the dipeptide at pH 6.0 with a bimolecular rate constant of 2.3+/-0.2 x 10(7) dm3 mol(-1)s(-1) suggesting that it reacts very selectively with the histidine moiety. Spectral observations at, or close to the end of this reaction show only the presence of a tyrosinyl free radical (TyrO.), however, indicating that fast (>10(6) s(-1) intramolecular charge transfer has taken place between histidine radicals (His+.) and tyrosine (TyrOH). This finding was supported by the direct observation of the rate of formation of TyrO. in experiments with the free amino acids, histidine and tyrosine, under conditions where Br2.- reacted selectively with histidine. The bimolecular rate constant for the reaction between His+. and TyrOH was found to be 2.4+/-0.5 x 10(6) dm3 mol(-1)s(-1). Taken together, the results of the study indicate that His+. is a relatively strong oxidising agent where (E (His+./His) > 770 mV at pH 6.0.     

Impairment of forearm vasodilatation to acetylcholine in hypercholesterolemia is reversed by aspirin

To study the intracellular apoptotic signaling pathways, we have established a cell-free system, in which DNA fragmentation of the isolated mouse liver nuclei was induced with lysates from the Fas-activated cells. We have found that the inactive nuclease present in the intact cell cytosol is activated by a caspase-3-like protease and the activated nuclease induces the nucleosomal DNA fragmentation. We attempted the purification of the inactive nuclease from bovine liver cytosol. The partially purified nuclease was activated by recombinant caspase-3, and to a lesser extent by caspase-6. The activated nuclease was able to digest plasmid DNA in addition to induce the DNA fragmentation of nuclei. DFF-45, which is a subunit of heterodimeric protein leading to DNA fragmentation upon its digestion by caspase-3, is found to inhibit the activity of the activated nuclease. These results suggest that the inactive nuclease in cytoplasm is converted to the active form by caspases, and the activated nuclease enters into nucleus to induce the DNA fragmentation. It is suggested that DFF-45 may function as an inhibitory factor of the caspase-sensitive nuclease in vivo.     

Impairment of nitric oxide-mediated relaxations in anaesthetized autoperfused streptozotocin-induced diabetic rats

This work was designed to determine in vivo the influence of the metabolic control of streptozotocin-induced diabetic rats, measured by the levels of haemoglobin glycosylation in blood (HbA1c), on developing vascular endothelial dysfunction. For this, the vasoactive responses to basal and stimulated endothelial nitric oxide (NO) were studied using the technique of the anaesthetized autoperfused rat, analyzing the responses to acetylcholine (ACh) and N(G)-nitro-L-arginine methyl ester (L-NAME) in non-diabetic and diabetic rats with different degrees of metabolic control (four groups with HbA1c levels of 5.5-7.4%, 7.5-9.4%, 9.5-12%, and >12%, respectively). When administered over a noradrenaline-induced vasopressor tone, ACh (0.25, 0.75, 2.5, 7.5 and 25 microg kg(-1)) induced dose-dependent vasodilatatory responses in all rat groups, reducing both mean arterial pressure and perfusion pressure of the left hindlimb. These responses were similar in non-diabetic and in diabetic rats with good metabolic control (HbA1c 5.5-7.4%), while diabetic rats with levels of HbA1c higher than 7.5% showed significantly lower vasodilatatory responses to ACh. In untreated diabetic rats, the relaxant responses evoked by the NO donor sodium nitroprusside were also impaired. On the other hand, increasing doses of L-NAME (0.1 to 10 mg kg(-1)) enhanced both mean arterial pressure and left hindlimb perfusion pressure in diabetic and non-diabetic rats. As with ACh, the responses to L-NAME were significantly reduced in diabetic rats with HbA1c levels higher than 7.5%. To determine the mechanism underlying the NO-mediated endothelial dysfunction, the responses to ACh in untreated diabetic rats (HbA1c >12%) were studied in the presence of the NO substrate L-arginine, in the presence of the oxygen-derived free radical scavenger superoxide dismutase (SOD), or in the presence of both compounds. Both L-arginine and SOD produced a partial improvement of the ACh-induced vasodilatatory responses, but the effects of these agents were not additive. In this group of animals, SOD also induced a partial recovery of the L-NAME-evoked vasoconstrictions. In non-diabetic and untreated diabetic rats, the plasma levels of NO derivatives and arginine were measured. No significant differences were obtained in the amount of nitrites plus nitrates, while plasma levels of arginine were markedly reduced in the untreated diabetic animals. The results indicate that the endothelial dysfunction associated to diabetes is closely related to the level of metabolic control of the disease. Therefore, it is possible to establish a threshold for developing endothelium impairment from percentages of HbA1c higher than 7.5%. As the responses to the NO synthase blocker L-NAME were analogously impaired, it is reasonable to suggest that diabetic endothelial dysfunction is related to the interference with mechanisms linked both to stimulated and basal production of NO. We suggest that this interference is partially due to a deficit in the substrate availability for NO and to an increased generation of superoxide anions.     

Glutathione transferase isoenzyme patterns in the rat ovary

It is well known that disturbance of calcium homeostasis has a significant role in the development of neurodegenerative disorders, such as Alzheimer's disease (AD). Our recent data suggest that acute treatment with the calcium antagonist verapamil can improve some behavioral deficits in an experimental model of AD. Therefore, the present study was done to establish the effect of chronically administered verapamil on cognitive and noncognitive behavior of rats with bilateral electrolitical lesions of nucleus basalis manocellularis (NBM)--an animal model of AD. The NBM lesions produce a deficit in performance of diverse behavior tests: active avoidance (AA), low level of fear (the open field test) as well as aggressive (the test of foot-shock induced aggression) and depressive (the learned helplessness test) behavior. Verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg i.p.) or saline solution (1 ml/kg i.p.) were injected 24 hr after the lesion of NBM and then repeatedly administered during the next 8 days (twice a day). Performance of the two-way active avoidance test, the open field test, the foot shock-induced aggression test and the learned helplessness test were done on day 4 after the last verapamil or saline treatment (day 13 after the lesion). Verapamil in doses of 2.5 and 5.0 mg/kg significantly ameliorated the deficit in the performance of AA, the open field behavior, and the depression, but not the aggressive behavior. The obtained beneficial effect of chronic administered verapamil suggests that the regulation of calcium homeostasis during the early period after NBM lesions might be a reasonable way to prevent the behavioral deficits in an experimental model of AD.     

Alterations in urinary bladder synaptosomal neurotransmitter concentrations in two-week streptozotocin-induced diabetic rats

Three-month-old male Wistar rats were rendered diabetic with a single intravenous injection of streptozotocin (60 mg/kg body weight). Two weeks after induction of diabetes, synaptosome-rich fractions were prepared from urinary bladder tissue homogenate of the diabetic rats and control rats by differential centrifugation (1000 x g, 17,000 x g and 100,000 x g) with discontinuous sucrose gradient. Synaptosomal acetylcholine, norepinephrine, epinephrine and dopamine were measured by the method of high-performance liquid chromatography. The respective neurotransmitter concentrations for the diabetic rats were 1537.8 +/- 65.3, 4757.7 +/- 361.9, 3720.7 +/- 276.1, and 2447.8 +/- 196.8 pmol/mg synaptosomal protein, respectively; those for the control rats were 338.1 +/- 25.0, 1009.0 +/- 54.6, 645.3 +/- 52.2, and 1426.1 +/- 123.9 pmol/mg protein, respectively. Thus, the synaptosomal concentrations for all the measured neurotransmitters were significantly higher in the diabetic rats (P < 0.05 for each comparison). In conclusion, it has been demonstrated that the vesicle-bound acetylcholine and catecholamines in the synaptosome-rich fraction of the urinary bladder were significantly increased in 2-week diabetic rats. This finding would suggest impaired neurotransmitter release from both the bladder sympathetic and parasympathetic efferent nerve endings in early streptozotocin-induced diabetes.     

Sodium, potassium-activated adenosine triphosphatase activity is impaired in the guinea pig pancreatic duct system in streptozotocin-induced diabetes

In patients with type I diabetes mellitus, clinical studies have demonstrated decreased secretion of pancreatic juice by the pancreatic excretory duct system. The cause of this decrease is unknown, but could involve changes in initial signal transduction pathways or one or more of the electrolyte transport components that subserve regulated fluid secretion. We have compared responsiveness to secretin in pancreatic ducts isolated from healthy and diabetic Hartley guinea pigs and also have compared the expression of CFTR and Na+, K(+)-ATPase in these two groups, as the activities of these two proteins are essential for secretion of pancreatic juice. The increases in cyclic AMP levels evoked by exposure to either 0.1 nM or 0.1 microM secretin were not significantly different in pancreatic ducts isolated from healthy and diabetic guinea pigs nor were levels of CFTR or Na+, K(+)-ATPase expression. By contrast, Na+, K(+)-ATPase activity in pancreatic ducts isolated from diabetic guinea pigs was decreased by 70%, suggesting a change in the enzyme's catalytic properties in the diabetic tissues. The observed decrease would be expected to seriously compromise the production of pancreatic juice.     

Effects of thyroid hormone on the sorbitol pathway in streptozotocin-induced diabetic rats

Sorbitol accumulation plays an important role in diabetic complications involving the kidney, nerves, retina, lens and cardiac muscle. To investigate the influence of thyroid hormone on the sorbitol pathway, we studied the effects of thyroid hormone on polyol metabolism in normal and diabetic rats. Rats were divided into three groups: controls, streptozotocin (STZ)-induced diabetic euthyroid rats (DM) and STZ-induced diabetic hyperthyroid (thyroxine-injected) rats (DM+HT). The sorbitol (Sor) concentrations in the kidney, liver and sciatic nerve (2.53+/-0.74, 0.97+/-0.16 and 24.0+/-5.1 nmol/mg protein, respectively) of the DM rats were significantly higher than those (1.48+/-0.31, 0.58+/-0.13 and 3. 1+/-0.6 nmol/mg protein) of the control rats. The Sor concentrations in the kidney and sciatic nerve of the DM+HT rats (1.26+/-0.29 and 9. 40+/-1.2 nmol/mg protein) were significantly lower than those in the DM rats. These values were reduced in the liver, unchanged in the kidney, and increased in the sciatic nerve from the hyperthyroid rats without diabetes. Thyroid hormone reduced the aldose reductase (AR) activities in the kidney, liver and sciatic nerve of the DM rats, and similarly reduced AR in the kidney and liver, but not in the sciatic nerve, of the non-diabetic rats. The sorbitol dehydrogenase (SDH) activities were decreased by thyroid hormone in the kidney and liver but not the sciatic nerve of DM rats. In the non-diabetic rats, this enzyme activity was decreased in liver, but not in kidney or sciatic nerve. A positive correlation between the Sor concentration and AR activity was observed in the kidney and liver but not in the sciatic nerve from control, DM and DM+HT rats. A negative correlation was observed between the Sor concentration and SDH activities in the same organs. These data suggest that thyroid hormone affects the sorbitol pathway, but the detailed mechanism whereby this hormone reduces the sorbitol content (especially in diabetic rats) remains to be clarified.