Nitric Oxide Donor Group Research Articles

Design, Synthesis, and Antisickling Investigation of a Nitric Oxide-Releasing Prodrug of 5HMF for the Treatment of Sickle Cell Disease.

5-hydroxyfurfural (5HMF), an allosteric effector of hemoglobin (Hb) with an ability to increase Hb affinity for oxygen has been studied extensively for its antisickling effect in vitro and in vivo, and in humans for the treatment of sickle cell disease (SCD). One of the downstream pathophysiologies of SCD is nitric oxide (NO) deficiency, therefore increasing NO (bio)availability is known to mitigate the severity of SCD symptoms. We report the synthesis of an NO-releasing prodrug of 5HMF (5HMF-NO), which in vivo, is expected to be bio-transformed into 5HMF and NO, with concomitant therapeutic activities. In vitro studies showed that when incubated with whole blood, 5HMF-NO releases NO, as anticipated. When incubated with sickle blood, 5HMF-NO formed Schiff base adduct with Hb, increased Hb affinity for oxygen, and prevented hypoxia-induced erythrocyte sickling, which at 1 mM concentration were 16%, 10% and 27%, respectively, compared to 21%, 18% and 21% for 5HMF. Crystal structures of 5HMF-NO with Hb showed 5HMF-NO bound to unliganded (deoxygenated) Hb, while the hydrolyzed product, 5HMF bound to liganded (carbonmonoxy-ligated) Hb. Our findings from this proof-of-concept study suggest that the incorporation of NO donor group to 5HMF and analogous molecules could be a novel beneficial strategy to treat SCD and warrants further detailed in vivo studies.

Hybrids as NO Donors.

Cinnamic acid and its derivatives have been studied for a variety of biological properties, including anti-inflammatory, antioxidant, anticancer, antihypertensive, and antibacterial. Many hybrids of cinnamic derivatives with other bioactive molecules have been synthesized and evaluated as nitric oxide (NO) donors. Since NO plays a significant role in various biological processes, including vasodilation, inflammation, and neurotransmission, NO donor groups are incorporated into the structures of already-known bioactive molecules to enhance their biological properties. In this review, we present cinnamic hybrids with NO-donating ability useful in the treatment of several diseases.

Electrochemical evidence of nitrate release from the nitrooxy compound 4-((nitrooxy) methyl)-3-nitrobenzoic acid and its antinociceptive and anti-inflammatory activities in mice

Considering the many biological activities of nitric oxide (NO), some lines of research focused on the modulation of these activities through the provision of this mediator by designing and synthesizing compounds coupled with an NO donor group. Thus, the objectives of the present study were to carry out an electrochemical investigation of the nitrooxy compound 4-((nitrooxy) methyl)-3-nitrobenzoic acid (1) and evaluate its activities and putative mechanisms in experimental models of pain and inflammation. Voltammetric studies performed in aprotic medium (mimetic of membranes) showed important electrochemical reduction mechanisms: nitroaromatic reduction, self-protonation, and finally reductive elimination, which leads to nitrate release. Systemic administration of the nitrooxy compound (1) inhibited the nociceptive response induced by heat and the tactile hypersensitivity and paw edema induced by carrageenan in mice. The activities in the models of inflammatory pain and edema were associated with reduced neutrophil recruitment and production of inflammatory cytokines, such as interleukin (IL)-1β, IL-6, tumor necrosis factor-α and CXCL-1, and increased production of IL-10. Concluding, electrochemical analysis revealed unequivocally that electron transfer at the nitro group of the nitrooxy compound (1) results in the cleavage of the organic nitrate, potentially resulting in the generation of NO. This electrochemical mechanism may be compared to a biochemical electron-transfer mediated nitrate release that, by appropriate in vivo bioreduction (enzymatic or not) would lead to NO production. Compound (1) exhibits activities in models of inflammatory pain and edema that may be due to reduced recruitment of neutrophils and production of inflammatory cytokines and increased production of IL-10. These results reinforce the interest in the investigation of NO donor compounds as candidates for analgesic and anti-inflammatory drugs.

Nitric oxide release from a biodegradable cysteine-based polyphosphazene.

Nitric oxide (NO) is a unique bioactive molecule that performs multiple physiological functions and has been found to exhibit antithrombotic, antimicrobial, and wound-healing effects as an exogenous therapeutic agent. NO release from polymeric materials intended for use in biomedical applications has been established to reduce their thrombogenicity and decrease the likelihood of infection and inflammation that frequently produce medical complications. As a result, numerous NO-releasing polymers have been developed in an effort to utilize the beneficial properties of NO to improve the performance of implantable materials. The majority of synthetic NO-releasing biodegradable polymers that have been reported to date are polyesters, and there is significant interest in the development of new NO-releasing materials with improved or distinctive physicochemical characteristics. Polyphosphazenes are polymers with inorganic phosphorus-nitrogen backbones, and hydrolytically-sensitive derivatives with organic substituents have been prepared that degrade under physiological conditions. For this reason, biodegradable poly(organophosphazenes) are interesting candidate materials for applications such as tissue engineering, where the addition of NO release capability may be therapeutically useful. Herein, we report the first development and characterization of an NO-releasing poly(organophosphazene) from poly(ethyl S-methylthiocysteinyl-co-ethyl cysteinyl phosphazene) (POP-EtCys-SH). The thiolated polymer was synthesized from the reaction of poly(dichlorophosphazene) with ethyl S-methylthiocysteinate, followed by partial cleavage of the disulfide linkages to form free thiol groups. The conversion of thiol to the NO-releasing S-nitrosothiol functional group with tert-butyl nitrite resulted in a polymer (POP-EtCys-NO) with an average NO content of 0.55 ± 0.04 mmol g-1 that was found to release a total of 0.35 ± 0.02 mmol NO g-1 over 24 h under physiological conditions (37 °C, pH 7.4 phosphate buffered saline). Extracts obtained from both the thiolated and S-nitrosated polymers were not found to significantly impair the viability of human dermal fibroblasts or induce morphological changes, indicating that this cysteine-based polyphosphazene may possess potential utility as an NO-releasing biomaterial.

Nitric oxide donors for cervical ripening in first-trimester surgical abortion.

Cervical priming before first-trimester surgical abortion is recommended in certain groups of women. Nitric oxide (NO) donors induce cervical ripening without uterine contractions, but the efficacy and side effects are of concern. To evaluate NO donors for cervical ripening before first-trimester surgical abortion, in terms of efficacy, side effects, and reduction of complications. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and POPLINE. We also searched reference lists of retrieved papers. We contacted experts in the field for information on both published and unpublished trials. Randomised controlled trials comparing NO donors alone or in combination with other methods for cervical ripening in first-trimester surgical abortion. Two review authors independently selected and extracted the data onto a data extraction form. We processed the data using Review Manager (RevMan 5) software. We included 9 studies involving 766 participants. There were no serious complications (infection requiring antibiotic treatment, blood transfusion, complications requiring unintended operation, cervical injury, uterine perforation, death or serious morbidity) in the included trials.NO donors were more effective in cervical ripening when compared with placebo or no treatment. Baseline cervical dilatation before the procedure was higher in NO donors group (mean difference (MD) 0.30, 95% confidence interval (CI) 0.01 to 0.58) The cumulative force required to dilate the cervix to 8 mm (MD -4.29, 95% CI -9.92 to 1.35), headache (risk ratio (RR) 1.73, 95% CI 0.86 to 3.46), abdominal pain (RR 0.87, 95% CI 0.50 to 1.50), or patient satisfaction (RR 0.95, 95% CI 0.84 to 1.07) were not different. More nausea and vomiting occurred in the women who received a NO donor (RR 2.62, 95% CI 1.07 to 6.45).NO donors were inferior to prostaglandins for cervical ripening. The cumulative force required to dilate the cervix to 8 mm to 9 mm was higher (MD 13.12, 95% CI 9.72 to 16.52), and baseline cervical dilatation was less (MD -0.73, 95% CI -1.01 to -0.45) in the NO donor group. However, the probability of dilation greater than 8 mm at three hours was higher in the NO donor group (RR 6.67, 95% CI 2.21 to 20.09). Side effects including headache (RR 5.13, 95% CI 3.29 to 8.00), palpitation (RR 3.43, 95% CI 1.64 to 7.15), dizziness (RR 3.29, 95% CI 1.46 to 7.41), and intraoperative blood loss (MD 33.59 ml, 95% CI 24.50 to 42.67) were also higher. However, abdominal pain (RR 0.33, 95% CI 0.25 to 0.44) and vaginal bleeding (RR 0.14, 95% CI 0.07 to 0.27) were less in the NO donor group. No difference for nausea/vomiting in both groups(RR 1.17, 95% CI 0.94 to 1.46). Patient satisfaction was not different.One trial compared a NO donor with a NO donor plus prostaglandin. The cumulative force required to dilate the cervix to 8 mm was higher (MD 14.50, 95% CI 0.50 to 28.50) in the NO donor group. There was no difference in headache (RR 0.88, 95% CI 0.38 to 2.00), abdominal pain (RR 0.14, 95% CI 0.02 to 1.07), or intraoperative blood loss (MD -50, 95% CI -164.19 to 64.19). NO donors are superior to placebo or no treatment, but inferior to prostaglandins for first-trimester cervical ripening, and associated with more side effects.

Exogenous intravascular nitric oxide enhances ventricular function after hemodilution with plasma expander

Aims This study evaluated the hypothesis that exogenous nitric oxide (NO) supplementation during acute hemodilution with plasma expander (PE) provides beneficial effects on cardiac function. Main methods Acute hemodilution in golden Syrian hamsters was induced by a 40% of blood volume exchange with dextran 70 kDa. Intravascular NO supplementation after hemodilution was accomplished with a NO donor, diethylenetriamine NONOate (DETA NONOate). The test group was treated with DETA NONOate, while the control group received only vehicle. Left ventricular cardiac function was studied using pressure–volume measurements obtained with a miniaturized conductance catheter. Key findings Cardiac output increased to 122 ± 5% and 107 ± 1% of the baseline in the group treated with NO donor and the vehicle group, respectively. Stroke work per stroke volume (SW/SV) after hemodilution reduced to 90% of the baseline and the NO donor significantly reduced SW/SV compared to the vehicle. The minimum rate of pressure change (dP/dt min) was significantly lower in animals treated with the NO donor compared to vehicle treated animals. Systemic vascular resistance (SVR) decreased to 62 ± 5% of the baseline in the NO donor group whereas the vehicle group SVR decreased to 83 ± 5% of the baseline. Using intravital microscopy analysis of microvessel in the dorsal skinfold window chamber, we established that the NO donor group induced significant vasodilation compared to the vehicle group. Significance NO supplementation in an acute hemodilution with PE has beneficial effects on cardiac performance. However, the NO supplementation effects with a NO donor are dose-independent and short-lasting.

Interaction between hydrogen sulfide and nitric oxide on cardiac protection in rats with metabolic syndrome.

To investigate the interaction between hydrogen sulfide (H2S)/cystathionine gamma-lyase (CSE) system and nitric oxide (NO)/nitric oxide synthase (NOS) system on cardiac protection in metabolic syndrome (MS) rats. Forty one male Sprague-Dawley rats were randomly divided into 6 groups: control group, MS group, H2S donor group, CSE inhibitor group, NOS inhibitor group, and NO donor group. The MS rat model was established by a high-fat diet of 16 weeks. Rats in control and MS groups were subjected to normal saline and the other four groups were respectively subjected to sodium hydrosulfide (NaHS, 56 μmol/kg), D,L-propargylglycine (PPG, 37.5 mg/kg), Nψ-nitro-L-arginine methyl ester (L-NAME, 18 mg/kg), L-Arginine (500 mg/kg) every day. Four weeks later, the obesity indices, blood sugar of oral glucose tolerance test in each time point (0,30,60, and 120 minutes) and blood lipids (cholesterol, triglyceride, high density lipoprotein, low density lipoprotein) were measured. The computer-based electrophysiological recorder system was used to measure the changes of the left ventricular systolic pressure (LVSP), the left ventricular end diastolic pressure (LVEDP), the maximal rate of pressure increase in the contraction phase (+dP/dtmax), and the maximal rate of pressure decrease in the diastole phase (-dP/dtmax). H2S and NO concentration in plasma and myocardium, as well as CSE, constitutive NOS (cNOS), and inducible NOS (iNOS) activities in myocardium were measured with colorimetric method. Reverse transcription-polymerase chain reaction was used to assess the gene expression of CSE and endothelial NOS (eNOS) mRNAs. Compared with control group, the obesity indices, blood sugar at each time point, and blood lipids significantly increased in MS group (P<0.05). H2S and NO concentration in plasma and myocardium, CSE and cNOS activities in myocardium, the expressions of CSE mRNA and eNOS mRNA, and the myocardial function significantly decreased in MS group (P<0.05). Compared with MS group, NO concentration in plasma and myocardium, cNOS and iNOS activities in myocardium, and the expression of eNOS mRNA significantly increased in CSE inhibitor group (P<0.05). However, activities of cNOS and iNOS in myocardium and the expression of eNOS mRNA were significantly decreased in H2S donor group (P<0.01), while the myocardial function significantly increased (P<0.05). H2S concentration in plasma and myocardium, and the expression of CSE mRNA significantly increased in NOS inhibitor group (P<0.05). However, in NO donor group, the CSE activity in myocardium and the expression of CSE mRNA significantly decreased (P<0.05). And the myocardial function was improved significantly (P<0.05). Both the H2S/CSE and NO/NOS systems appear to have a mutual down-regulation effect on myocardium in MS rats. Meanwhile, exogenous H2S and NO supplement is cardioprotective in rat model of MS.

Effects of chronic treatment with a low dose of nicorandil on the function of the rat aorta during ageing

1. It is known that ATP-sensitive potassium (K(ATP)) channels regulate the membrane potential of smooth muscle cells and vascular tone. Because their activity is altered during ageing, many pharmacological treatments aimed at improving K(ATP) channel and cardiovascular functions have been evaluated. Nicorandil, a K(ATP) channel opener, nitric oxide (NO) donor and anti-oxidant, induces vasodilation, decreases blood pressure and exhibits cardioprotection in ageing, as well as after ischaemia-reperfusion. 2. In the present study, using tension myography and biochemical and histological techniques, we investigated the effects of chronic (2 months) low-dose nicorandil (0.1 mg/kg per day) treatment on the function of rat aorta during ageing (in 4-, 12- and 24-month old rats). 3. The results showed that chronic nicorandil treatment significantly improves mechanical relaxation and noradrenaline-induced vasoconstriction in aged rats. At all ages, the nicorandil-induced vasodilation was primarily mediated by its NO donor group. Nicorandil treatment resulted in an additional 0.5-1 elastic lamella in the aorta and decreased total protein, collagen and elastin content in the aortic wall at all ages. However, in 4-month-old rats, nicorandil significantly increased the elastin : total protein ratio by 19%. 4. In contrast with results of previous studies that used high doses of nicorandil (i.e. 60 mg/kg per day), low-dose nicorandil treatment in the present study did not lead to a progressive desensitization to nicorandil and may be beneficial in improving arterial function in ageing or cardiovascular diseases.

The Role of Nitric Oxide in the Expression of Renal Aquaporin 2 in a Cirrhotic Rat Model: Does an AVP-Independent Mechanism Exist for the Regulation of AQP2 Expression?

The aquaporin (AQP) water channel is expected to play a decisive role of hyponatremia and water retention in cirrhotic patients. Despite the importance of the water channel, however, previous findings vary widely when it concerns AQP2 of the kidneys in subjects with cirrhosis. The purpose of this study was to investigate the expression of AQP2 in the distal renal tubule in cirrhosis, and the presence of the nitric oxide-AQP2 signaling pathway as a possible vasopressin-aquaporin-independent pathway. Sixty male Wister rats were assigned to six groups: (1) control; (2) TAA (thioacetamide); (3) TAA with nitric oxide donor; (4) TAA with nitric oxide inhibitor; (5) TAA with HMG CoA reductase inhibitor; (6) TAA with tetrahydrobiopterin. Immunohistochemical staining for AQP2, real-time polymerase chain reaction (PCR) for AQP2 and 3, citrulline assay, and renal cGMP concentration were measured. The AQP2-positivity of cirrhotic rats were higher than the controls (P < 0.05). The AQP2-positivity decreased in the nitric oxide donor group, but the proportion rose back up when the subjects were injected with the nitric oxide inhibitor (P < 0.05). The expression of AQP2 and AQP3 mRNA was also found to show an increase in the cirrhotic group as compared with the normal controls (P < 0.05). The cirrhotic group administered with nitric oxide donor showed a significant decline in the expression of the mRNA. The control group's cGMP concentration was lower than that of the cirrhotic group (P < 0.05), but a comparison of the two groups injected with nitric oxide modulators, such as statin and BH4, did not show significant differences in the cGMP concentration level. The expression of AQP2 of the kidneys increased in the cirrhotic rats. AQP2 had relations to the activity changes of nitric oxide synthetase.

The nitrosylated flurbiprofen derivative HCT1026 inhibits cytokine-induced signalling through a novel mechanism of action

We have previously shown that the nitrosylated flurbiprofen derivative HCT1026 inhibits bone resorption, both in vivo and in vitro, and that its mechanism of action is independent of nitric oxide release and prostaglandin synthesis inhibition. Here we describe the effects of HCT1026 on osteoclast formation, activity, survival and cell signalling in vitro. HCT1026 strongly inhibited osteoclast formation, activity and survival in murine osteoclast cultures, whereas macrophages and osteoblasts were unaffected. HCT1026 induced osteoclast apoptosis, and this was partially prevented by increasing the concentration of receptor activator of nuclear factor kappa B ligand (RANKL). This suggests that HCT1026 inhibits bone resorption by inhibiting the effects of RANKL. In agreement with this we found that HCT1026 inhibited RANKL-induced activation of the nuclear factor kappa B (NFκB) and extracellular signal-regulated kinase (ERK) pathways in both osteoclast and macrophage cultures, whereas its parent compound flurbiprofen did not. In addition, HCT1026 also inhibited tumor necrosis factor (TNF)-, interleukin-1 (IL1)- and LPS-induced signalling, but not macrophage colony stimulating factor induced signalling. The pathways that are inhibited by HCT1026 all share a similar kinase complex upstream of the NFκB and ERK pathways, and this is the most likely target for the actions of HCT1026. Although the rationale for the modification of flurbiprofen with a nitric oxide donor group was to prevent gastro-intestinal toxicity, the resulting compound HCT1026 gained unexpected additional cytokine-inhibitory properties. As RANKL, TNF and IL1 are all important mediators of inflammation and joint destruction, compounds like HCT1026 could represent a novel class of anti-inflammatory compounds.

Nitroaspirin corrects immune dysfunction in tumor-bearing hosts and promotes tumor eradication by cancer vaccination.

Active suppression of tumor-specific T lymphocytes can limit the immune-mediated destruction of cancer cells. Of the various strategies used by tumors to counteract immune attacks, myeloid suppressors recruited by growing cancers are particularly efficient, often resulting in the induction of systemic T lymphocyte dysfunction. We have previously shown that the mechanism by which myeloid cells from tumor-bearing hosts block immune defense strategies involves two enzymes that metabolize L-arginine: arginase and nitric oxide (NO) synthase. NO-releasing aspirin is a classic aspirin molecule covalently linked to a NO donor group. NO aspirin does not possess direct antitumor activity. However, by interfering with the inhibitory enzymatic activities of myeloid cells, orally administered NO aspirin normalized the immune status of tumor-bearing hosts, increased the number and function of tumor-antigen-specific T lymphocytes, and enhanced the preventive and therapeutic effectiveness of the antitumor immunity elicited by cancer vaccination. Because cancer vaccines and NO aspirin are currently being investigated in independent phase I/II clinical trials, these findings offer a rationale to combine these treatments in subjects with advanced neoplastic diseases.

Exogenous and Endogenous Nitric Oxide Donors Improve Post-Ischemic Tissue Oxygenation in Early Pancreatic Ischemia/Reperfusion Injury in the Rat

Introduction: In pancreatic ischemia/reperfusion (IR) injury (IRI) the role of nitric oxide (NO) is not completely understood. Using a rat model of normothermic in situ IRI, the effect of endogenous and exogenous NO donors on post-ischemic tissue oxygenation and tissue damage was investigated. Methods: IR was induced by 2-hour normothermic in situ ischemia of a pancreatic tail segment pedunculated on the splenic vessels with 2 h of reperfusion in an untreated, an L-arginine- and a sodium-nitroprusside-treated group (Wistar rats, n = 7/group). Animals without ischemia served as controls. Tissue oxygenation (pO_2ti) was monitored using a pO₂-sensitive Clark-type electrode. Histological investigation was performed following a semiquantitative score (edema, vacuolization, PMN infiltration, necrosis). Plasma lipase was another marker of organ damage. Results: The administration of L-arginine and sodium nitroprusside caused a significant amelioration of the decrease in pO_2ti after reperfusion compared to IR animals (p < 0.05). Histological damage was also reduced in the NO donor groups (p < 0.05). After reperfusion, plasma lipase in the L-arginine-treated animals was significantly lower compared to IR and sodium nitroprusside (p < 0.05). Conclusions: The administration of both endogenous and exogenous NO donors is protective in IRI of the rat pancreas which can be seen by an improvement in post-ischemic tissue oxygenation which indicates better nutritive tissue perfusion, amelioration of the histological tissue injury and, in L-arginine animals, lower lipase levels. NO donors could be useful in the prevention and reduction of the pancreatic IRI.

Influence of nitric oxide on microcirculation in pancreatic ischemia/reperfusion injury: an intravital microscopic study

Abstract Recently, protective effects of nitric oxide donors in pancreatic ischemia/reperfusion (IRI) injury have been described. Their role in post-ischemic microcirculation was previously not investigated. Ischemia reperfusion was induced in an isolated pancreatic tail segment in situ. Animals were randomized to four experimental groups (n= 7 animals/group), the control group (CO) received saline as placebo. Treatment groups received either sodium nitroprusside (SN) 5 min before until 2 h after reperfusion, l-arginine (LA) 30 min before reperfusion until 2 h after reperfusion or sodium nitroprusside and l-arginine (SNLA) together. After induction of ischemia (2 h) post-ischemic microcirculation was observed for 2 h by intravital-fluorescence microscopy. Functional-capillary density (FCD), leukocyte adherence in post-capillary venules (LAV) and histological damage were analysed. After reperfusion FCD decreased in all groups (p<0.05). FCD was significantly restored in all groups with administration of nitric oxide donors after reperfusion (p<0.05) as compared to CO without significant difference between the individual nitric oxide donor groups. Leukocyte adherence was significantly increased 1 h and 2 h after reperfusion (p<0.001) as compared to baseline, which was lower in all nitric oxide donor groups. Histological damage in the pancreatic tail-segment was significantly reduced in nitric oxide donor groups (p<0.01). Administration of nitric oxide donors might be useful in ischemia-reperfusion injury of the pancreas by its protective effect on microcirculation and inflammatory reaction.

Influence of nitric oxide on microcirculation in pancreatic ischemia/reperfusion injury: an intravital microscopic study

Recently, protective effects of nitric oxide donors in pancreatic ischemia/reperfusion (IRI) injury have been described. Their role in post-ischemic microcirculation was previously not investigated. Ischemia reperfusion was induced in an isolated pancreatic tail segment in situ. Animals were randomized to four experimental groups (n=7 animals/group), the control group (CO) received saline as placebo. Treatment groups received either sodium nitroprusside (SN) 5 min before until 2 h after reperfusion, L-arginine (LA) 30 min before reperfusion until 2 h after reperfusion or sodium nitroprusside and L-arginine (SNLA) together. After induction of ischemia (2 h) post-ischemic microcirculation was observed for 2 h by intravital-fluorescence microscopy. Functional-capillary density (FCD), leukocyte adherence in post-capillary venules (LAV) and histological damage were analysed. After reperfusion FCD decreased in all groups (P<0.05). FCD was significantly restored in all groups with administration of nitric oxide donors after reperfusion (P<0.05) as compared to CO without significant difference between the individual nitric oxide donor groups. Leukocyte adherence was significantly increased 1 h and 2 h after reperfusion (P<0.001) as compared to baseline, which was lower in all nitric oxide donor groups. Histological damage in the pancreatic tail-segment was significantly reduced in nitric oxide donor groups (P<0.01). Administration of nitric oxide donors might be useful in ischemia-reperfusion injury of the pancreas by its protective effect on microcirculation and inflammatory reaction.

Ultrastructural study of pleural lymphatic drainage unit and effect of nitric oxide on the drainage capacity of pleural lymphatic stomata in the rat

The objective of this study was twofold: first to investigate the ultrastructure of the lymphatic drainage unit on the costal pleura of rats by electron microscopy, and secondly to examine the effect of nitric oxide on the pleural lymphatic stomata and fluid absorption from the pleural cavity. The lymphatic drainage unit of the rat costal pleura is composed of three special components: the lymphatic stomata between the mesothelial cells, the initial part of the lymphatic vessels and the underlying connective tissue containing many foramina. The unit is the main passage to drainage fluid, particles and cells in the pleural space. To investigate the regulator of the lymph drainage, nitric oxide synthase inhibitor and nitric oxide donor were injected into the peritoneal cavity of the rats, respectively. Trypan blue was used as tracer. The ultrastructural changes of pleural lymphatic stomata were observed under scanning electron microscope and analyzed by a computer image processing system. It turned out that the area and density of the pleural lymphatic stomata were positively correlated with the nitric oxide quantity (p < 0.05). After the tracer was injected into the pleural cavity, the nitric oxide donor group exhibited a higher trypan blue concentration than the control group (p < 0.05). The ability of the pleura to absorb trypan blue was enhanced because of the larger opening of the lymphatic stomata (p < 0.05). It is suggested that nitric oxide can increase lymphatic absorption of the pleura by opening pleural lymphatic stomata.

Effect of nitric oxide on exercise-induced proteinuria in rats.

Temporary proteinuria occurring after exercise is a common finding, and it is explained predominantly by alterations in renal hemodynamics. In this study, we investigated whether nitric oxide (NO), which is known to have an effect on renal hemodynamics and to increase during exercise, has a role in postexercise proteinuria. In the first step of this study, the effect of acute NO synthase blockage on exercise proteinuria was evaluated. The urinary protein levels in animals that performed acute exhaustive treadmill running exercise were considerably elevated compared with the control animals. Significantly elevated urinary protein levels were also detected in animals that received Nomega-nitro-L-arginine methyl ester before exhaustion, compared with both control and exhausted groups, and mixed-type proteinuria was detected in electrophoresis, as in all exhausted animals. In the second step of the study, a NO donor (isosorbide mononitrate) was given to rats 1 h before exhaustive exercise. Mixed-type proteinuria and the elevation in urinary protein levels that occur as a consequence of exhaustive exercise were prevented by NO donor treatment. Finally, in the third step of our study, a calcium channel blocker (diltiazem), another vasodilator, was applied to the rats 1 h before exhaustive exercise. Urinary protein levels were not different in exhausted rats with or without calcium channel blocker treatment. On the other hand, in both groups, urinary protein levels were higher than in the control group. The tail-cuff blood pressure alterations caused by vasodilator drug applications before exercise were not different for NO donor and calcium channel blocker groups. These results suggest that endogenous NO might prevent the postexercise proteinuria from becoming more severe by affecting hemodynamic changes that occur during exercise.

Effect of Nitric Oxide in Ischemia/Reperfusion of the Pancreas

Background. Ischemia/reperfusion injury, and thus graft pancreatitis, remains a major problem in pancreas transplantation. Contradictory results about the role of nitric oxide (NO) in pancreatic ischemia/reperfusion have been reported; however, in none of the reports has a detailed comparison between inhibition of NO synthase and NO supplementation been carried out.Methods. Vascular isolation of the pancreatic tail was performed in landrace pigs. After splenectomy catheters placed in the distal part of the splenic vessels allowed collection of the venous effluent and perfusion of the pancreatic tail. Three hours of complete warm ischemia was followed by 6 h of reperfusion. The effect of the NO donor sodium nitroprusside (SNP) and l-arginine was compared to a control group and NO synthase inhibition with l-NAME.Results. Lipase in the venous effluent of the pancreas was significantly decreased in the SNP and the l-arginine groups. Vascular resistance was markedly elevated in the l-NAME group and reduced in the NO donor groups. Tissue pO2 after reperfusion was only significantly elevated in the SNP group. Granulocyte infiltration and also overall histological tissue injury were most severe in the control group followed by the l-NAME group, the SNP group, and the l-ARG group.Conclusion. The data show that supplementation of nitric oxide is clearly protective in pancreatic ischemia/reperfusion. However, inhibition of NO synthesis does not lead to an equally clear aggravation of tissue injury.

Antisecretory and gastroprotective activities of compounds endowed with H 2 antagonistic and nitric oxide (NO) donor properties

In spite of the well recognized gastric antisecretory activity, the gastroprotective potential of histamine H 2 receptor antagonists is controversial. Most clinical studies in fact indicate that these drugs do not substantially protect the gastric mucosa from aggressive factors. Nitric oxide (NO) has been recently recognized as a fundamental mediator in gastric defence mechanisms, due to its ability to increase gastric mucosal blood flow and mucus production and to inhibit neutrophils adherence to endothelial cells. The aim of this study was to investigate the gastroprotective and H 2 receptor antagonistic activity of a series of lamtidine analogues which contain different NO-releasing moieties (furoxan, nitroxy and nitrosothiol). These compounds were tested, in comparison with related H 2 antagonists devoid of NO-donor structures, in different H 2 receptor assays and in the conscious rat against 0.6 N HCl-induced gastric lesions. All the compounds tested were able to antagonize histamine-mediated responses at cardiac and gastric H 2 receptors; however, furoxan and nitroxy derivatives were 10-fold less potent than the analogues devoid of NO-donor properties. By contrast, NO-donor compounds were more active than reference H 2 antagonists as gastroprotective agents against mucosal injury induced by 0.6 N HCl. Among the different NO-donor moieties, the furoxan group conferred to the H 2 antagonist molecule the highest gastroprotective potential; this finding closely correlates with the characteristics of NO release. In conclusions, lamtidine-analogue H 2 antagonists combined with NO-donor moieties are endowed with gastric antisecretory and protective activity and could be the prototypes of a new class of anti-ulcer drugs. Finally, the furoxan NO donor group seems to be the most favourable among the different moieties tested.