Effects of streptozotocin-induced diabetes on acetylcholine metabolism in rat brain

The main objective of this study was to determine whether uncontrolled hyperglycemia, as a consequence of diabetes, altered the metabolism of acetylcholine (ACh) in rat brain. To accomplish this, rats received injections of streptozotocin (STZ, 60 mg/kg, i.v.) or vehicle, and were maintained for up to 7 weeks after the injections. Various indices of ACh metabolism were determined in striatum and hippocampus, two brain regions densely innervated by cholinergic neurons. STZ induced diabetes in 96% of the rats injected, as evidenced by glucose spillage into the urine within 48 hours. Serum glucose levels increased to 326% of control values by 1 week and remained at this level for the duration of the study. The steady-state concentrations of ACh and choline, determined in brain tissue from animals killed by head-focused microwave irradiation, did not differ between the control and STZ-injected groups. However, the synthesis and release of neurotransmitter by striatal slices, measured in vitro, decreased in a time-dependent manner. Although the basal release of ACh was unaltered at 1 week, neurotransmitter release decreased significantly by 21% at 5 weeks and by 26% at 7 weeks. The release of ACh evoked by incubation with 35 mM KCl was inhibited significantly by 20% at all time points studied. ACh synthesis by slices incubated under basal conditions decreased by 13% and 27% at 5- and 7-weeks, respectively, the latter significantly less than controls. Synthesis by striatal slices incubated with 35 mM KCl was inhibited by 17% at 7 weeks. Although the synthesis and release of ACh by hippocampal slices from diabetic animals tended to be less than controls, these alterations were not statistically significant. Investigations into the mechanism(s) mediating the deficit in ACh synthesis exhibited by striatal slices indicated that it did not involve alterations in precursor choline availability, nor could it be attributed to alterations in the activities of the synthetic or hydrolytic enzymes choline acetyltransferase or acetylcholinesterase; rather, the decreased turnover of ACh may be secondary to other STZ-induced, hyperglycemia-mediated neurochemical alterations.     

Effects of short term experimental diabetes on brain serotonin metabolism

Serotonin metabolism was studied in several brain regions of control and Streptozotocin-treated male Wistar rats. After induction of diabetes, the animals were killed at 24 hours. Concentrations of brain tryptophan show a generalized increase in all brain regions, being only significant in medulla-pons. Serotonin levels do not change, while 5-HIAA concentrations, as well as the ratio 5-HIAA/5-HT, show significant increases in medulla-pons and mid-brain.     

Effects of clofibrate on plasma tryptophan, growth hormone, and prolactin and on brain tryptophan and serotonin in prepubertal rats

The effects of clofibrate administration (200 mg/kg, po) on somatic growth, plasma levels of lipids, tryptophan, growth hormone (GH), and prolactin (PRL), as well as on brain concentrations of tryptophan and 5-hydroxytryptamine (5-HT) were studied in prepubertal male rats. The drug did not significantly alter ponderal growth, but an appreciable reduction of tail length was observed in rats treated for 30 days. Triglyceride concentrations in plasma showed a 43% diminution after 30 days of treatment, whereas free fatty acid (FFA) levels were not modified. Clofibrate administration for 7, 15, or 30 days caused a fall in total tryptophan and a significant increase of the free fraction in plasma with no change in brain tryptophan levels. Brain 5-HT was generally unaffected but a marked elevation of this parameter was noted in rats treated for 15 days. Plasma GH and PRL concentrations remained unaltered. It may be concluded from these findings that the slight reduction of somatic growth, the diminution of triglycerides, and the increase of free tryptophan in plasma, induced by chronic clofibrate treatment, are not associated with variations in brain tryptophan and 5-HT levels or with modifications of plasma GH and PRL titers.     

Effects of gallic acid on brain lipid peroxide and lipid metabolism in streptozotocin-induced diabetic Wistar rats

This study evaluated the protective effects of gallic acid on brain lipid peroxidation products, antioxidant system, and lipids in streptozotocin-induced type II diabetes mellitus. Streptozotocin-induced diabetic rats showed a significant increase in the levels of blood glucose, brain lipid peroxidation products, and lipids and a significant decrease in the activities of brain enzymic antioxidants. Oral treatment with gallic acid (10 mg and 20 mg/kg) for 21 days significantly decreased the levels of blood glucose, brain lipid peroxidation products, and lipids and significantly increased the activities of brain enzymic antioxidants in diabetic rats. Histopathology of brain confirmed the protective effects of gallic acid. Furthermore, in vitro study revealed the free radical scavenging action of gallic acid. Thus, our study shows the beneficial effects of gallic acid on brain metabolism in streptozotocin-induced type II diabetic rats. A diet containing gallic acid may be beneficial to type II diabetic patients.     

Influence of streptozotocin-induced diabetes and insulin on the functional capacity of rats

Male Sprague-Dawley rats were assigned to three groups designated as diabetic, diabetic-plus-insulin, and control and tested for maximum oxygen consumption (VO2max) and maximum heart rate on three different occasions during the 6- to 8-wk experimental period. Compared with the prediabetic values and the means of the other two groups, diabetic animals had significantly higher submaximum and lower maximum VO2 values. These relationships prevailed when the groups were evaluated in terms of ml.kg-1.min-1 or ml.(kg0.79-1).min-1. In addition, the diabetic animals had significantly lower submaximum and maximum heart rates and shorter run times. Daily injections of insulin (2 U.day-1.rat-1) restored VO2max to within the limits of the control animals but did not normalize heart rates or run-time values. The linear relationship between heart rates and VO2 was repeatedly demonstrated with normal animals. However, this relationship progressively declined with the time course of diabetes. These results indicate that, in untreated diabetes, functional capacity is markedly reduced with the progression of the disease and suggest that alterations in the autonomic nervous system, tissue metabolic capacity, and decreases in lean body mass are responsible for the changes noted.     

Effects of dietary pyrazinamide, an antituberculosis agent, on the metabolism of tryptophan to niacin and of tryptophan to serotonin in rats

The effects of pyrazinamide on the metabolism of tryptophan to niacin and of tryptophan to serotonin were investigated to elucidate the mechanism for pyrazinamide action against tuberculosis. Weanling rats were fed with a diet with or without 0.25% pyrazinamide for 61 days. Urine samples were periodically collected for measuring the tryptophan metabolites. The administration of pyrazinamide significantly increased the metabolites, 3-hydroxyanthranilic acid and beyond, especially quinolinic acid, nicotinamide, N'-methylnicotinamide, and N1-methyl-4-pyridone-3-carboxamide, and therefore significantly increased the conversion ratio of tryptophan to niacin and the blood NAD level . However, no difference in the upper metabolites of the tryptophan to niacin pathway such as anthranilic acid, kynurenic acid and xanthurenic acid was apparent between the two groups. No difference in the concentrations of trytptophan and serotonin in the blood were apparent either. It is suggested from these results that the action of pyrazinamide against tuberculosis is linked to the increase in turnover of NAD and to the increased content of NAD in the host cells.     

Effects of streptozotocin-induced diabetes mellitus on hypothalamic-pituitary-thyroid axis in rats

The effects of streptozotocin-induced diabetes mellitus on the hypothalamic-pituitary-thyroid axis in rats were studied. Streptozotocin (60 mg/kg) was injected ip. Rats were decapitated at two and four weeks after the streptozotocin treatment. Thyrotropin releasing hormone (TRH), thyrotropin (TSH), thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2) and 3',5'-diiodothyronine (3',5'-T2) were measured by means of the specific radioimmunoassay for each. Immunoreactive TRH (ir-TRH) contents in the hypothalamus significantly decreased at four weeks (p less than 0.02). Basal TSH levels in plasma significantly decreased (p less than 0.005, p less than 0.001), and plasma ir-TRH and TSH responses to cold were significantly inhibited after the streptozotocin treatment (p less than 0.001). The plasma TSH response to TRH was decreased, but not significantly. The plasma T4 and T3 levels fell significantly. RT3 did not change throughout the experiment. 3,3'-T2 levels in plasma fell significantly, whereas 3',5'-T2 increased. Blood glucose levels rose significantly after streptozotocin treatment, but insulin treatment led to partial restoration. The findings suggest that streptozotocin-induced diabetes mellitus affects various sites of the hypothalamic-pituitary-thyroid axis in rats.     

Effects of streptozotocin-induced diabetes on lung mechanics and biochemistry in rats

Young and adult rats were given a single intraperitoneal injection of 75 mg/kg streptozotocin in citrate buffer and were compared with age- and weight-matched controls that received an equal volume of buffer alone. Studies done 8 wk after the injections showed that final body weight, lung dry weight, lung DNA content, and air and saline lung volumes were significantly lower in both young and adult diabetic rats compared with the controls. In young diabetic rats, volume-pressure (V-P) curves expressed as percent maximal lung volume (%MLV) were shifted downward and to the right of those in young control rats at 5 cmH2O transpulmonary pressure (PL) for air and at 4, 6, and 8 cmH2O PL for saline-filled lungs; specific lung compliance (CL) values obtained from both air and saline V-P curves were significantly reduced, and concentration of hydroxyproline relative to DNA was significantly increased. In adult diabetic rats, V-P curves expressed in %MLV, CL values, and concentrations of protein and hydroxyproline were similar to those in adult control rats. We conclude that in both young and adult rats, diabetic state leads to somatic and lung growth retardation. In addition in young diabetic rats lung distensibility is decreased. An increase in the concentration of some connective tissue proteins may be responsible for the latter observation.     

Dose-response decrease in plasma tryptophan and in brain tryptophan and serotonin after tryptophan-free amino acid mixtures in rats

Rats fasted 15 hours were treated p.o. with increasing amounts (660 and 1320 mg/kg body weight) of a mixture containing a fixed proportion of seven essential amino acids (L-phenylalanine 13.6%, L-leucine 6.0%, L-isoleucine 12.1%, L-methionine 12.1%, L-lysine 30.3%, L-threonine 10.6%, L-valine 15.2%) and lacking tryptophan. The mixtures produced a dose-response decrease of free (by 34% after the lower dose and by 58% after the higher dose of the mixture) and total (by 10 and 31%) plasma tryptophan and of brain tryptophan (by 38 and 65%), serotonin (by 17 and 41%) and 5-hydroxyindole acetic acid (by 21 and 49%). The mechanisms of these changes are discussed.     

The effect of streptozotocin-induced diabetes and of insulin supplementation on glycogen metabolism in rat liver.

The effects of streptozotocin-induced diabetes and of insulin supplementation to diabetic rats on glycogen-metabolizing enzymes in liver were determined. The results were compared with those from control animals. The activities of glycogenolytic enzymes, i.e. phosphorylase (both a and b), phosphorylase kinase and protein kinase (in the presence or in the absence of cyclic AMP), were significantly decreased in the diabetic animals. The enzyme activities were restored to control values by insulin therapy. Glycogen synthase (I-form) activity, similarly decreased in the diabetic animals, was also restored to control values after the administration of insulin. The increase in glycogen synthase(I-form) activity after insulin treatment was associated with a concomitant increase in phosphoprotein phosphatase activity. The increase in phosphatase activity was due to (i) a change in the activity of the enzyme itself and (ii) a decrease in a heat stable protein inhibitor of the phosphatase activity.     

The effect of agmatine on L-arginine metabolism in erythrocytes under streptozotocin-induced diabetes in rats

The effects of agmatine on oxidative and nonoxidative metabolic pathways of L-arginine were investigated both in plasma and erythrocytes under experimental diabetes mellitus. It was indicated, that agmatine prevents the development of oxidative-nitrosative stress in diabetic rats. After treatment of animals by agmatine NO-synthase methabolic pathway of L-arginine is depressed whereas arginase one increases in erythrocytes of rats with experimental diabetes mellitus.     

Effects of streptozotocin-induced diabetes on neuronal sigma receptors in the rat brain

To study the effect of diabetes mellitus on the density of sigma receptors, in vitro binding experiments were conducted in whole brain homogenate membranes of 5-week and 10-week control rats and streptozotocin (STZ)-induced diabetic rats. sigma-1 Receptors were labelled with [3H](+)-pentazocine while sigma-2 receptors were labelled with [3H] 1,3-di-o-tolylguanidine (DTG) in the presence of 0.5 microM (+)-pentazocine to mask sigma-1 sites. Non-specific binding was determined in the presence of 20 microM haloperidol. Scatchard analysis revealed a 27% (p<0.01) decreased in sigma-1 receptor density and a 33% (p<0.01) decreased in sigma-2 receptor density in whole brain of 10-week STZ-diabetic rats. No statistically significant difference was found in the sigma receptor content of 5-week STZ-diabetic rats. These results provide evidence that neuronal sigma receptors are reduced in 10-week STZ-diabetic rats and suggest that changes in sigma receptors may play a role in diabetes related abnormalities. Further evaluation is required to determine whether changes observed in the brain are homogeneous for either or both sigma receptor subtypes as well as potential links between other CNS receptor changes previously observed in STZ-induced diabetic rats.     

Enzymes of myo-inositol and inositol lipid metabolism in rats with streptozotocin-induced diabetes.

Diabetes, with only mild ketosis, was induced in male rats by a single injection of streptozotocin. After 12 weeks the specific activities of enzymes concerned with the metabolism of inositol and of inositol lipids were measured in various tissues. Inositol 1-phosphate synthase (EC 5.5.1.4) was most active in testis and the activity was significantly less in diabetic rats than in controls on a similar diet. Inositol oxygenase (EC 1.13.99.1), which converts myo-inositol into glucuronic acid, was also less active in kidney from diabetic animals. CDP-diacylglycerol-inositol phosphatidyltransferase (EC 2.7.8.11) and phosphatidylinositol 4-phosphate kinase (EC 2.7.1.68) showed decreased specific activities in brain and sciatic nerve of diabetic rats. By contrast the diabetic state did not affect the specific activities of phosphatidylinositol kinase (EC 2.7.1.67) or phosphatidylinositol 4,5-bisphosphate phosphatase (EC 3.1.3.36) in these tissues. The results are discussed in relation to diabetic neuropathy.     

Sevoflurane reduces ischemic brain injury in rats with diet and streptozotocin-induced diabetes

Abstract

To investigate the role of S100B, oxidative stress and the apoptosis signaling pathways in the sevoflurane induced neuroprotective effect on stroke. The brain injury, molecular and cellular damage, and functional recovery were investigated upon ischemic brain injury followed by sevoflurane treatment. Longa rodent stroke scales was used to quantify neurological deficits. TTC staining was used to measure infarct volume of brain tissue. Absolute brain water content was measured by wet/dry weight method. The neuronal morphological change was assessed by H and E staining. The spatial learning and memory ability were measured by water maze test. Serum proteins including S100B, GSH-PX, SOD, Bcl-2, Bax, Caspase-3 were measured by ELISA. The level of NOS and NO in serum was determined by colorimetric method. Compared with control, the serum proteins including S100B, Bax, NO, Caspase-3, and NOS activity in cerebral infarction rats increased significantly while SOD, GSH-PX, and Bcl-2 decreased significantly. Diabetic mellitus complicated with cerebral infarction rats showed more dramatic increase for S100B, Bax, NO, Caspase-3, and NOS activity and dramatic decrease for SOD, GSH-PX, and Bcl-2. Interestingly, sevoflurane reduced the changes significantly. The S100B level positively correlated with brain damage, NO, Bax, caspase-3, and NOS activity but negatively correlated with SOD, Bax, and GSH-PX. Brain damage in sevoflurane groups decreased while behavior outcomes including Longa neurologic score, learning, and memory increased significantly. The neuroprotective effect of sevoflurane is associated with defense mechanisms against free radical-induced oxidative stress and inhibition of apoptosis. S100B protein correlated with oxidative stress and the apoptosis signaling pathways.     

Effects of streptozotocin-induced long-term diabetes on parietal cell function and morphology in rats

Gastric pathology is a common complication in diabetes mellitus. The aim of the study was to evaluate the functions and morphological changes of the parietal cells of the rat stomach after streptozotocin-induced diabetes. Diabetes mellitus was induced in Wistar rats by a single intraperitoneal injection of streptozotocin (60 mg/kg body weight). The rats were weighed weekly and sacrificed after 6 months. The glandular portion of the stomach was removed and processed for H⁺-K⁺-ATPase immunohistochemistry and light and electron microscopy studies. Acid secretion was measured in vivo. After 6 months of diabetes, the mean weight of the rats was significantly lower (P < 0.001) compared to control. The mean weight of the stomach to body weight percentage increased significantly (P < 0.001) compared to control. The blood glucose level in diabetic rats was significantly higher (P < 0.001) than in normal control. Diabetic rats showed significant (P < 0.001) decrease in basal and stimulated acid secretion when compared to control. Electron micrographs of the parietal cells of glandular stomach of diabetic rats revealed significant (P < 0.0002) reduction in the number of mitochondria and a small though not significant increase in the number of canaliculi in the parietal cells compared with normal. Immunohistochemistry showed reduced H⁺-K⁺-ATPase (P < 0.00001) compared to control. Long-term diabetes induces morphological as well as functional changes in gastric parietal cells. The decrease in the number of mitochondria accompanied by reduced in H⁺-K⁺-ATPase in parietal cells may explain the reduced acid secretion observed in diabetics.