Quercetin, a flavonoid antioxidant, modulates endothelium-derived nitric oxide bioavailability in diabetic rat aortas

The present work examined the effect of chronic oral administration of quercetin, a flavonoid antioxidant, on blood glucose, vascular function and oxidative stress in STZ-induced diabetic rats. Male Wistar-Kyoto (WKY) rats were randomized into euglycemic, untreated diabetic, vehicle (1% w/v methylcellulose)-treated diabetic, which served as control, or quercetin (10mgkg(-1) body weight)-treated diabetic groups and treated orally for 6 weeks. Quercetin treatment reduced blood glucose level in diabetic rats. Impaired relaxations to endothelium-dependent vasodilator acetylcholine (ACh) and enhanced vasoconstriction responses to alpha(1)-adrenoceptor agonist phenylephrine (PE) in diabetic rat aortic rings were restored to euglycemic levels by quercetin treatment. Pretreatment with N(omega)-nitro-l-arginine methyl ester (l-NAME, 10microM) or methylene blue (10microM) completely blocked but indomethacin (10microM) did not affect relaxations to ACh in aortic rings from vehicle- or quercetin-treated diabetic rats. PE-induced vasoconstriction with an essentially similar magnitude in vehicle- or quercetin-treated diabetic rat aortic rings pretreated with l-NAME (10microM) plus indomethacin (10microM). Quercetin treatment reduced plasma malonaldehyde (MDA) plus 4-hydroxyalkenals (4-HNE) content as well as increased superoxide dismutase activity and total antioxidant capacity in diabetic rats. From the present study, it can be concluded that quercetin administration to diabetic rats restores vascular function, probably through enhancement in the bioavailability of endothelium-derived nitric oxide coupled to reduced blood glucose level and oxidative stress.     

Tissue specific expression and immunohistochemical localization of glutathione S-transferase in streptozotocin induced diabetic rats: modulation by Momordica charantia (karela) extract

In streptozotocin (STZ)-induced diabetes, destruction of pancreatic beta-cell causes an acute shortage of insulin. Increased oxidative stress is believed to be one of the main factors in the etiology and complications of diabetes. In this study we have reported hyperglycemia and glutathione-associated oxidative stress in rats one week after treatment with STZ. In our previous studies, we have reported oxidative stress-related changes in xenobiotic metabolism in tissues from STZ-induced chronic diabetic rats. Here, we demonstrate by immunohistochemistry, that glutathione S-transferase (GST) isoenzymes are differentially expressed in the liver, kidney and testis of diabetic rats. The distribution of GST isoenzymes was found to be tissue- and regio-specific. In addition, we have also shown that treatment with an extract of Momordica charantia (karela), an antidiabetic herb, modulates GST expression in diabetic rats and reverts them to the normal distribution as seen in the tissues of control rats. These results suggest that glutathione metabolism and GST distribution in the tissues of diabetic rats may play an important role in the etiology, pathology and prevention of diabetes.     

Differences in the nitric oxide metabolism in streptozotocin-treated rats and children suffering from Type 1 diabetes

The relationship between diabetes mellitus Type 1 and nitric oxide (NO) synthesis was studied in multiple low-dose streptozotocin (STZ)-treated rats and diabetic children. The aim of our experimental work was to test the effect of hyperglycemic state on the level of urinary stable NO end products and on the expression of inducible nitric oxide synthase (NOS II) in white blood cells (WBC). It was also studied whether the measurements of these parameters were suitable to predict the presence of early diabetes before its onset. The occurrence of insulitis in streptozotocin-treated rats could not be clearly demonstrated. Urinary nitrite plus nitrate level significantly increased both in diabetic rats and in children compared to controls. However, the increase of the activity and the expression of inducible NOS II were only observed in rat white blood cells and this effect was prevented by insulin treatment. In human samples, less than 25% of children showed elevated NOS II expression in white blood cells without any correlation to the level of urinary NO end products and glycated hemoglobin in blood. Correlation was found only between the activity and expression of NOS II in white blood cells of patients whose white blood cells were positive for the presence of NOS II. Measurement of urinary nitrite plus nitrate content as well as the determination of NOS II expression of white blood cells in an early phase of diabetes are not suitable predictors in humans probably due to the basic differences in the mechanism of streptozotocin-induced rat and spontaneous human Type 1 diabetes.     

Endothelial nitric oxide synthase activation contributes to post-exercise hypotension in spontaneously hypertensive rats

We investigated the role that endothelial nitric oxide synthase plays in post-exercise hypotension in spontaneously hypertensive rats. To accomplish this, rats were subjected to a single bout of dynamic exercise on a treadmill at 15 m/min for 20 min. l-Nitroarginine methyl ester (l-NAME, 40 mg/kg, i.p.) significantly inhibited post-exercise hypotension (25 ± 11 and 5 ± 3 mm Hg, respectively; P < 0.05). In addition, the superoxide anion generation was decreased, while the plasma nitrite production and serine phosphorylation of endothelial nitric oxide synthase were significantly elevated in spontaneously hypertensive rats at 30 min after the termination of exercise. Taken together, these data demonstrate that the increased phosphorylation of endothelial nitric oxide synthase plays a crucial role in the reduction of arterial pressure following a single bout of dynamic exercise in spontaneously hypertensive rats.     

Seasonality in expression and distribution of nitric oxide synthase isoforms in the testis of the catfish, Clarias batrachus: Role of nitric oxide in testosterone production

Nitric oxide (NO) is a well-recognized versatile signaling molecule. It is produced by catalytic action of nitric oxide synthase (NOS) on L-arginine in a variety of animal tissues. Existence of different isoforms of NOS has been shown in mammalian testis, but report on their presence in the testis of ectothermic vertebrates is non-existent. This study demonstrates the differential expressions of two isoforms of nitric oxide synthase (neuronal-nNOS and inducible-iNOS) like molecules in different cell types in the testis of seasonally breeding catfish, Clarias batrachus through immunohistochemistry. Positive immunoprecipitation of nNOS and iNOS like molecules were detected in germ cells as well as interstitial cells only in the recrudescing and fully mature fish. The immunoreactions differed in intensity and varied with changing reproductive status. Treatment of adult male fish with NO donor, sodium nitroprusside, and a NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME) increased and decreased the total nitrate and nitrite concentration in the testis, respectively. Sodium nitroprusside and L-NAME also induced simultaneous decline and rise in the testicular testosterone level, respectively. These findings, thus, suggest that NOS isoforms are expressed variedly in different cell types in the testis of reproductively active fish. This investigation also suggests that NO inhibits testosterone production in the testis.     

Effects of cold exposure and shear stress on endothelial nitric oxide synthase activation

Endothelial nitric oxide synthase (eNOS) is the primary enzyme that produces nitric oxide (NO), which plays an important role in blood vessel relaxation. eNOS activation is stimulated by various mechanical forces, such as shear stress. Several studies have shown that local cooling of the human finger causes strong vasoconstriction, followed after several minutes by cold-induced vasodilation (CIVD). However, the role played by endothelial cells (ECs) in blood vessel regulation in respond to cold temperatures is not fully understood. In this study, we found that low temperature alone does not significantly increase or decrease eNOS activation in ECs. We further found that the combination of shear stress with temperature change leads to a significant increase in eNOS activation at 37 °C and 28 °C, and a decrease at 4 °C. These results show that ECs play an important role in blood vessel regulation under shear stress and low temperature.     

Calreticulin Transacetylase mediated activation of human platelet nitric oxide synthase by acetyl group donor compounds

Polyphenols have attracted immense interest because of their diverse biological and pharmacological activities. Surprisingly, not much is documented about the biological activities of acetoxy derivatives of polyphenol called polyphenolic acetates (PA). In our previous reports, we have conclusively established the Calreticulin Transacetylase (CRTAase) catalyzed activation of neuronal nitric oxide synthase (nNOS) and tumor necrosis factor-α (TNF-α) induced nitric oxide synthase (iNOS) by PA. In the present work, specificity of CRTAase to various classes of PA was characterized in human platelet. The effect of PA, on platelet NOS and intracellular cyclic guanosine monophosphate (cGMP), and adenosine diphosphate (ADP)-induced platelet aggregation were studied in an elaborated manner. Platelet CRTAase exhibited differential specificities to polyphenolic acetates upon incubation with l-arginine leading to activation of NOS. The intraplatelet generation of NO was studied by flowcytometry using DCFH-DA. The differential specificities of CRTAase to PA were found to positively correlate with increased production of NO upon incubation of PRP with PA and l-arginine. Further, the inhibitory effect of l-NAME on PA induced NO formation in platelets substantiated the CRTAase catalyzed activation of NOS. The real-time RT-PCR profile of NOS isoforms confirmed the preponderance of eNOS over iNOS in human platelets on treatment with PA. Western blot analysis also reiterated the differential pattern of acetylation of eNOS by PA. PA were also found effective in increasing the intraplatelet cGMP levels and inhibiting ADP-induced platelet aggregation. It is worth mentioning that the effects of PA were found to be in tune with the specificities of platelet CRTAase to PA as the substrates.     

Effects of leptin on oxidative stress in healthy and Streptozotocin-induced diabetic rats

Aims/hypothesis It is generally accepted that oxidative stress is responsible for etiology and complications of diabetes. During uncontrolled Type 1 diabetes, plasma leptin levels rapidly fall. However, it is not known whether diabetes-induced hypoleptinemia has any role in oxidative stress related to uncontrolled Type I diabetes. The present study was designed to examine the effects of leptin treatment on plasma lipid peroxidation and reduced glutathion of normal and streptozotocin(STZ)-induced diabetic rats. Methods Diabetes was induced by single injection of Streptozotocin (55 mg/kg bw). One week after induction of diabetes, rats began 5-day treatment protocol of leptin injections of (0.1 mg/kg bw i.p.) or same volume vehicle. At the end of the 5th day, rats were sacrificed by cardiac puncture under anesthesia and their plasma was taken for plasma leptin, malondialdehyde, and reduced glutathione measurements. Results Plasma leptin levels decreased in STZ-induced diabetic rats while plasma glucose, TBARS, and GSH levels increased. Plasma leptin levels were not affected with leptin treatment in both diabetic and non-diabetic rats. The elevation in plasma TBARS associated with STZ diabetes decreased with leptin treatment. Leptin also increased plasma GSH levels in diabetic rats. In non-diabetic rats, treatment with leptin did not change plasma TBARS and GSH levels. Conclusions/interpretations In conclusion, leptin treatment is able to attenuate lipid peroxidation in STZ-diabetic rats, in the onset of diabetes, by increasing the GSH levels without affecting hyperglycemia and hypoleptinemia.     

Sequential changes in redox status and nitric oxide synthases expression in the liver after bile duct ligation

Bile duct ligation (BDL) in rats induces portal fibrosis. This process has been linked to changes in the oxidative state of the hepatic cells and in the production of nitric oxide. Our objective was to find possible temporal connections between hepatic redox state, NO synthesis and liver injury. In this work we have characterized hepatic lesions 17 and 31 days after BDL and determined changes in hepatic function, oxidative state, and NO production. We have also analyzed the expression and localization of inducible NO synthase (NOS2) and constitutive NO synthase (NOS3). After 17 and 31 days from ligature, lipid peroxidation is increased and both plasma concentration and biliary excretion of nitrite+nitrate are rised. 17 days after BDL both NOS2 and NOS3 are expressed intensely and in the same regions. 31 days after BDL, the expression of NOS2 remains elevated and is localized mostly in preserved hepatocytes in portal areas and in neighborhoods of centrolobulillar vein. NOS3 is localized in vascular regions of portal spaces and centrolobulillar veins and in preserved sinusoids and although its expression is greater than in control animals (34%), it is clearly lower (50%) than 17 days after BDL. The time after BDL is crucial in the study of NO production, intrahepatic localization of NOS isoforms expression, and cell type involved, since all these parameters change with time. BDL-induced, peroxidation and fibrosis are not ligated by a cause-effect relationship, but rather they both seem to be the consequence of common inductors.     

The effects of folic acid and nitric oxide synthase inhibition on coronary flow and oxidative stress markers in isolated rat heart

The aim of this study was to assess the effects of folic acid on coronary flow and oxidative stress markers with or without non-specific inhibition of nitric oxide synthase by l-NAME in isolated rat hearts. The hearts of male Wistar albino rats (n = 12, age 8 weeks, body mass 180–200 g) were retrograde perfused according to the Langendorff technique at gradually increased constant perfusion pressure (40–120 cmH₂O). Coronary flow and markers of oxidative stress: nitrite outflow, superoxide anion production, and index of lipid peroxidation (by measuring thiobarbituric acid reactive substances) in coronary effluent were calculated. The experiments were performed during control conditions and in presence of folic acid (100 μM) alone or folic acid (100 μM) plus l-NAME (30 μM). Control values of coronary flow varied in range from 4.37 ± 0.10 ml/min/g wt at 40 cmH₂O to 12.05 ± 0.42 ml/min/g wt at 120 cmH₂O. Nitrite outflow varied from 1.68 ± 0.17 nmol/min/g wt at 40 cmH₂O to 3.56 ± 0.17 nmol/min/g wt at 120 cmH₂O and was parallel with coronary perfusion pressure-coronary flow curve. Folic acid significantly increased coronary flow (40–120 cmH₂O, 5.63 ± 0.10 ml/min/g wt and 15.2 ± 0.42 ml/min/g wt, respectively) and was accompanied by significant increase in nitrite outflow (2.28 ± 0.29 nmol/min/g wt at 40 cmH₂O to 6.66 ± 0.50 nmol/min/g wt at 120 cmH₂O). In addition, folic acid significantly decreased superoxide anion production especially at upper coronary perfusion pressure values (60% at 120 cmH₂O) and increased index of lipid peroxidation (37.16% at 120 cmH₂O), respectively. Folic acid plus l-NAME did not change control values of coronary flow significantly. However, folic acid plus l-NAME increased nitrite outflow especially at upper coronary perfusion pressure values (43.05% at 120 cmH₂O) and did not change significantly superoxide anion production or index of lipid peroxidation versus control values, respectively. The results clearly showed that on isolated rat hearts at gradually increased constant perfusion pressure, folic acid increased coronary flow, increased nitrite outflow, decreased superoxide anion production, and increased index of lipid peroxidation. These effects were reversed or blocked by l-NAME thus demonstrating mediation or at least participation of NO in the mechanism of the folic acid-induced effects.     

Inhibition of nitric oxide synthase enhances contractile response of ventricular myocytes from streptozotocin-diabetic rats

The contractile hyporesponsiveness of the streptozotocin diabetic rat heart in vitro to β-adrenergic agonists is eliminated when the heart is perfused with N^G-nitro-l-arginine methyl ester (l-NAME), a non-selective inhibitor of nitric oxide synthase (NOS). The following study evaluated the hypothesis that an increased production of NO/cGMP within the diabetic myocyte inhibits the β-adrenergic-stimulated increase in calcium current and contractile response. Male Sprague-Dawley rats were given an intravenous injection of streptozotocin (60 mg/kg). After 8 weeks, L-type calcium currents were recorded in ventricular myocytes using the whole cell voltage-clamp method. Shortening of isolated myocytes was determined using a video edge detection system. cAMP and cGMP were measured using radioimmunoassay. Nitric oxide production was determined using the Griess assay kit. Basal cGMP levels and nitric oxide production were elevated in diabetic myocytes. Shortening of the diabetic myocytes in response to isoproterenol (1 μM) was markedly diminished. However, there was no detectable difference in the isoproterenol-stimulated L-type calcium current or cAMP levels between control and diabetic myocytes. Acute superfusion of the diabetic myocyte with l-NAME (1 mM) decreased basal cGMP and markedly enhanced the shortening response to isoproterenol but did not alter isoproterenol-stimulated calcium current. These data suggest that increased production of NO/cGMP within the diabetic myocyte suppressed β-adrenergic stimulated shortening of the myocyte. However, NO/cGMP apparently does not suppress shortening of the myocyte by inhibition of the β-stimulated calcium current.     

Endothelial nitric oxide synthase genotype and haplotype are not associated with diabetic retinopathy in diabetes type 2 patients

Polymorphisms in the endothelial nitric oxide synthase (eNOS) gene have been associated with the development of diabetic retinopathy (DR) in patients with type 1 diabetes mellitus (T1DM), but not with T2DM. However, no previous study has analyzed combinations of genetic markers (haplotypes), which can be more informative. We studied three eNOS genetic polymorphisms: a single nucleotide polymorphism in the promoter region (T(-786)C), in exon 7 (Glu298Asp), and a variable number of tandem repeats in intron 4 (b/a) in 103 healthy controls, and in 170 patients with T2DM (without DR, N=114; with DR, N=56). We also examined the association of eNOS gene haplotypes with T2DM and with DR. No differences were found in the frequencies of genotypes and alleles of the three polymorphisms among the three groups of subjects. However, the "C-Glu-b" haplotype was more common in healthy controls (24%) than in T2DM patients (7%) (P=0.0001). Finally, no significant difference in the distribution of eNOS haplotypes frequencies was found when T2DM patients with or without DR were compared (P=0.7372). These findings suggest no association between DR and individual eNOS haplotypes in T2DM patients. The "C-Glu-b" haplotype, however, may have a protective effect against T2DM. Further studies should be conducted to address the molecular basis for such an effect.     

Endothelium-dependent vasorelaxation is inhibited by in vivo depletion of vascular thiol levels: Role of endothelial nitric oxide synthase

Thiols like glutathione may serve as reducing co-factors in the production of nitric oxide (NO) and protect NO from inactivation by radical oxygen species. Depletion of thiol compounds reduces NO-mediated vascular effects in vitro and in vivo. The mechanisms underlying these actions are not clear, but may involve decreased synthesis of NO and/or increased degradation of NO. This study investigates the effect of glutathione depletion on the response to NO-mediated vasodilation induced by acetylcholine (Ach, 10 μg/kg), endothelial NO synthase (eNOS) activity and potential markers of vascular superoxide anion (O^·-₂) production in conscious chronically catheterized rats. Thiol depletion induced by buthionine sulfoximine (BSO, 1 g ip within 24 h) decreased the hypotensive effect of Ach by 30% (MAP reduction before BSO 27 ± 3 mmHg, 19 ± 3 mmHg after BSO, (mean ± SEM), p < .05n = 8). The impaired effect of Ach was associated with a significant reduction in eNOS activity (control: 7.7 ± 0.8, BSO: 3.9 ± 0.4 pmol/min/mg protein (p < .05), n = 6). In contrast, neither NADH/NADPH driven membrane-associated oxidases nor lucigenin reductase activity were significantly (p < .05) affected by BSO (BSO: 4415 ± 123, control: 4105 ± 455 counts/mg, n = 6) in rat aorta. It is concluded that in vivo thiol depletion results in endothelial dysfunction and a reduced receptor-mediated vascular relaxation. This effect is caused by reduced endothelial NO formation.     

Carvacrol partially reverses symptoms of diabetes in STZ-induced diabetic rats

Little is known about the protective effects of carvacrol on the symptoms of streptozotocin induced diabetes in rats. Hence, this present study was designed to evaluate the protective effect of the strong antioxidant, carvacrol, on the symptoms of streptozotocin induced diabetes in rats. Carvacrol at the doses of 25 and 50 mg/kg body weight were orally administered to diabetic rats for a period of 7 days after the onset of diabetes. Food-water intake and body weight changes were daily recorded. Biochemical parameters such as serum glucose, insulin, total cholesterol, alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase were measured. Although treatment of diabetic rats with oral administration of carvacrol resulted in a slight reduction in serum glucose level and significant reduction in serum total cholesterol, alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase in comparison with diabetic control rats, there were no significant differences in serum insulin levels, food-water intake values and body weight changes. Despite the inadequacy of carvacrol on diabetes treatments, it was determined to have at least a partially protective role on liver enzymes.     

Glutamate-induced activation of nitric oxide synthase is impaired in cerebral cortex in vivo in rats with chronic liver failure

It has been proposed that impairment of the glutamate-nitric oxide-cyclic guanosine monophosphate (cGMP) pathway in brain contributes to cognitive impairment in hepatic encephalopathy. The aims of this work were to assess whether the function of this pathway and of nitric oxide synthase (NOS) are altered in cerebral cortex in vivo in rats with chronic liver failure due to portacaval shunt (PCS) and whether these alterations are due to hyperammonemia. The glutamate-nitric oxide-cGMP pathway function and NOS activation by NMDA was analysed by in vivo microdialysis in cerebral cortex of PCS and control rats and in rats with hyperammonemia without liver failure. Similar studies were done in cortical slices from these rats and in cultured cortical neurons exposed to ammonia. Basal NOS activity, nitrites and cGMP are increased in cortex of rats with hyperammonemia or liver failure. These increases seem due to increased inducible nitric oxide synthase expression. NOS activation by NMDA is impaired in cerebral cortex in both animal models and in neurons exposed to ammonia. Chronic liver failure increases basal NOS activity, nitric oxide and cGMP but reduces activation of NOS induced by NMDA receptors activation. Hyperammonemia is responsible for both effects which will lead, independently, to alterations contributing to neurological alterations in hepatic encephalopathy.     

Prolonged relaxation consistent with persistent soluble guanylyl cyclase activation in canine pulmonary artery following brief treatment with nitric oxide donors

Recent work has indicated that prolonged treatment with nitric oxide (NO) donors results in tissue storage of NO as S-nitrosothiols and N-nitrosamines. The possibility thus exists that NO treatment may result in the development of tissue stores of NO with functionally significant effects following removal of the original NO source. In these studies, the effects of 10 min treatment with two chemically distinct NO sources, S-nitrosoglutathione (GSNO) and (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NO) were determined in canine pulmonary artery using a superfusion system that permitted continuous isometric force recording during addition and removal of the NO donors. Relaxation that persisted for up to 1 h after removal of the NO source, was demonstrated for both NO sources, but at lower concentrations relative to the relaxant EC(50) for GSNO versus DEA-NO. Persistent relaxation with both NO sources was fully reversed by both the sGC inhibitor, ODQ, and an inhibitor of cGMP-dependent protein kinase, Rp-8-Br-PET-cGMPS, indicating that persistent relaxation was consistent with persistent activation of the sGC-cGMP signaling pathway. In separate measurements, a GSNO-induced persistent increase in both tissue cGMP ([cGMP](i)) and relaxation were fully reversed by both ODQ and the thiol reducing agent dithiothreitol (DTT). The results indicate that vascular smooth muscle is capable of converting short-lived NO responses following short term exposure to NO donors by a mechanism consistent with prolonged sGC activation, resulting in persistent relaxation. Reversal of this cGMP-dependent process with DTT suggests that it occurs via mechanisms that are thiol redox sensitive.     

Effects of nitric oxide synthase inhibitors on systemic hypotension, cytokines and inducible nitric oxide synthase expression and lung injury following endotoxin administration in rats

Endotoxin shock is characterized by systemic hypotension, hyporeactiveness to vasoconstrictors and acute lung edema. A nitric oxide synthase (NOS) inhibitor, N^G-monomethyl-L-arginine (L-NMMA) has been shown to be effective in reversing acute lung injury. In the present study, we evaluated the effects of NOS blockade by different mechanisms on the endotoxin-induced changes. In anesthetized rats, lipopolysaccharide (LPS,Klebsiella pneumoniae) was administered intravenously in a dose of 10 mg/kg. LPS caused sustained systemic hypotension accompanied by an eightfold increase of exhaled NO during an observation period of 4 h. After the experiment, the lung weight was obtained and lung tissues were taken for the determination of mRNA expressions of inducible NOS (iNOS), interleukin-1 (IL-1) and tumor necrosis factor--(TNF-). Histological examination of the lungs was also performed. In the control group injected with saline solution, mRNA expressions of iNOS, IL-1 and TNF- were absent. Four hours after LPS, the mRNA expressions of iNOS and IL-1 were still significantly enhanced, but TNF- was not discernibly expressed. LPS also caused a twofold increase in lung weight. Pathological examination revealed endothelial damage and interstitial edema. Various NOS inhibitors were given 1 h after LPS administration. These agents included N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), a constitutive NOS and iNOS inhibitor; S,S-1,4-phenylene-bis-(1,2-ethanedinyl) bis-isothiourea dihydrobromide (1,4-PBIT, 10 mg/kg), a relatively specific iNOS inhibitor, and dexamethasone (3 mg/kg), an inhibitor of iNOS expression. These NOS inhibitors all effectively reversed the systemic hypotension, reduced the exhaled NO concentration and prevented acute lung injury. The LPS-induced mRNA expressions of iNOS and IL-1 were also significantly depressed by these NOS inhibitors. Our results suggest that NO production through the iNOS pathway is responsible for endotoxin-induced lung injury. Certain cytokines such as IL-1 are possibly involved. These changes are minimized by NOS inhibitors through different mechanisms.     

Enhanced expression of neuronal nitric oxide synthase in islets of exercise-trained rats

It is well known that glucose-stimulated insulin secretion (GSIS) decreases after exercise training. In the present study, we investigated the effects of exercise training (9 weeks of running) on the activity of glucokinase (GK), the production of nitric oxide (NO), and the protein expressions of both glucose transporter-2 (GLUT-2) and NO synthase (NOS) in rat pancreatic islets. Exercise training significantly reduced GSIS, with decreases in GK activity and GLUT-2 protein expression. The NO releases and cGMP contents were higher in the islets of trained rats than in those of control rats. Exercise training enhanced cNOS activity, the protein expression of both neuronal nitric oxide synthase (nNOS) and calmodulin, and NADPH-cytochrome c reductase activity in the homogenates of islets. Thus, exercise training-induced reduction of GSIS would result from, at least in part, decreases in both glucose entry and the first step in glycolytic utilization of glucose. Moreover, exercise training could enhance the protein expression of nNOS, which in turn enhances two catalytic activities of nNOS, an NO production and a cytochrome c reductase activity.