Nonspecific inhibition of nitric oxide synthesis evokes endothelin-dependent increases in myocardial contractility.

The role of endogenous nitric oxide (NO) in modulating myocardial contractility is still unclear, in part because of unknown, secondary effects of blocking NO release. We hypothesized that the nonspecific inhibition of nitric oxide synthase (NOS) enhances endothelin-1 (ET-1) effects, which can play a role in ET-A receptor-dependent myocardial contractile responses. The myocardial contractility was estimated from the slope of the left ventricular end-systolic pressure-diameter relationship in closed-chest, pentobarbital-anesthetized dogs. Group 1 (n = 7) was the saline-treated control, while in groups 2 (n = 7) and 3 (n = 7) N-nitro-l-arginine (NNA, 4 mg kg(-1)), a nonselective NOS blocker, was administered with or without pretreatment with the ET-A receptor antagonist ETR-P1/fl peptide (100 nmol kg(-1) iv). Plasma ET-1, nitrite/nitrate (NO(x)) and blood superoxide levels were measured, and myocardial ET-1 content and xanthine oxidoreductase (XOR) activity were determined from myocardial biopsies. The infusion of NNA over 120 min decreased the plasma NO(x), significantly elevated the plasma ET-1 and blood superoxide levels, and in parallel greatly increased the left ventricular contractility as compared with the untreated controls [47.5 vs 30 mm Hg mm(-1)]. The myocardial ET-1 content decreased simultaneously, while the XOR activity and blood superoxide level were significantly elevated. These effects, including NNA-induced positive inotropy, were significantly suppressed by pretreatment with ETR-P1/fl peptide. These results demonstrate that a diminished NO synthesis leads to a preponderant ET-1 effect, which increases myocardial contractility through an ET-A receptor-dependent mechanism.

Oral phosphatidylcholine pretreatment decreases ischemia-reperfusion-induced methane generation and the inflammatory response in the small intestine.

We have shown that phosphatidylcholine (PC) metabolites may have a function in counteracting the production of reactive oxygen species (ROS), and that this mechanism can lead to the generation of methane from choline. The aims were to establish whether the dietary administration of PC can protect the reperfused small bowel mucosa by its acting as an anti-inflammatory agent and to investigate this possibility in association with in vivo methane generation. Group 1 (n = 5) of anesthetized dogs served as sham-operated controls, whereas in groups 2 (n = 6) and 3 (n = 6), complete small intestinal ischemia was induced by occluding the superior mesenteric artery for 60 min. Groups 1 and 2 were fed with normal laboratory chow for 1 week before the experiments, whereas the animals in group 3 received a special diet containing 1% soybean PC. The intramucosal pH and the difference of the arterial and local PCO2 (PCO2 gap) were detected by indirect tonometry. Intestinal superoxide production and myeloperoxidase (MPO) activity (a marker of tissue leukocyte infiltration) were ascertained on ileal biopsy samples 180 min after reperfusion. The content of methane in the exhaled air was determined by gas chromatography. I/R was characterized by significant tissue acidosis with ROS generation and elevated MPO activity. These changes were accompanied by increased methane production in the exhaled air during reoxygenation. The PC-enriched diet prevented the decrease in intramucosal pH, diminished the intestinal superoxide generation and the MPO activity, and significantly decreased the exhaled methane concentration. The increased dietary uptake of PC exerts an anti-inflammatory influence in the gastrointestinal tract. Exhaled methane is linked to abnormal ROS generation; a decreased methane production is associated with significantly reduced inflammatory activation during I/R.

Hypoxia-induced generation of methane in mitochondria and eukaryotic cells: an alternative approach to methanogenesis.

BACKGROUND/AIMS: Electrophilic methyl groups bound to positively charged nitrogen moieties may act as electron acceptors, and this mechanism could lead to the generation of methane from choline. The aims were to characterize the methanogenic potential of phosphatidylcholine metabolites, and to define the in vivo relevance of this pathway in hypoxia-induced cellular responses. METHODS: The postulated reaction was investigated (1) in model chemical experiments, (2) in rat mitochondrial subfractions and (3) in bovine endothelial cell cultures under hypoxic conditions and in the presence of hydroxyl radical generation. The rate of methane formation was determined by gas chromatography with flame-ionisation detectors. The lucigenin-enhanced chemiluminescence assay was used to determine the reactive oxygen species-scavenging capacity of the choline metabolites. RESULTS: Significant methane generation was demonstrated in all three series of experiments. Phosphatidylcholine metabolites with alcoholic moiety in the molecule (i.e. choline, N,N-dimethylethanolamine and N-methylethanolamine), inhibited oxygen radical production both in vitro and in vivo, and displayed an effectiveness proportional to the amount of methane generated and the number of methyl groups in the compounds. CONCLUSION: Methane generation occurs in aerobic systems. Phosphatidylcholine metabolites containing both electron donor and acceptor groups may have a function to counteract intracellular oxygen radical production.

Systemic phosphatidylcholine pretreatment protects canine esophageal mucosa during acute experimental biliary reflux.

AIM: To characterize the consequences of short-term exposure to luminal bile on mucosal mast cell reactions in a canine model, and to determine the effects of systemic phosphatidylcholine pretreatment in this condition. METHODS: Twenty mongrel dogs were used for experiments. Group 1 (n = 5) served as a saline-treated control, while in group 2 (n = 5) the esophagus was exposed to bile for 3 h. In group 3 (n = 5) the animals were pretreated with 7-nitroindazole to inhibit the neuronal isoform of nitric oxide synthase. In group 4 (n = 5) phosphatidylcholine solution (50 mg/kg) was administered iv before the biliary challenge. Mucosal microcirculation was observed by intravital videomicroscopy. Myeloperoxidase and nitric oxide synthase activities, the degrees of mast cell degranulation and mucosal damage were evaluated via tissue biopsies. RESULTS: Exposure to bile evoked significant mast cell degranulation and leukocyte accumulation. The red blood cell velocity and the diameter of the postcapillary venules increased significantly. The tissue ATP content and constitutive nitric oxide synthase activity decreased, while the inducible nitric oxide synthase activity increased significantly as compared to the control values. 7-nitroindazole treatment significantly exacerbated the mucosal mast cell degranulation and tissue damage. In contrast, phosphatidylcholine pretreatment prevented the bile-induced ATP depletion, the inducible nitric oxide synthase and myeloperoxidase activity and the mast cell degranulation increased. CONCLUSION: The neuronal nitric oxide synthase--mast cell axis plays an important role in the esophageal mucosal defense system. Systemic phosphatidylcholine pretreatment affords effective protection through ameliorating the bile-induced ATP depletion and secondary inflammatory reaction.

[Effects of phosphatidylcholine pretreatment during acute experimental biliary reflux]. / Foszfatidilkolin elokezelés hatása kísérletes epés reflux akut szakaszában.

UNLABELLED: Biliary regurgitation plays important role in gastro-esophageal reflux disease and postoperative complications. Our major aims were to find out the consequences of short-term exposure with luminal bile on mucosal microcirculation and nitric oxide synthesis, and to determine the effects of systemic phosphatidylcholine pretreatment in this condition. The experiments were performed on inbred mongrel dogs. Group 1 (n=5) served as a saline-treated control, while in group 2 (n=5) the esophagus was exposed to bile for 3 h. In group 3 (n=5) the animals were pre-treated with 7-nitroindazole (7-NI), to inhibit the neuronal isoform of nitric oxide synthase. In group 4 (n=5) phosphatidylcholine (PC) solution (50 mg/kg) was administered iv before the biliary challenge. The microcirculation of the mucosa was observed by intravital videomicroscopy; myeloperoxidase and nitric oxide synthase activities, the degree of mast cell degranulation and tissue damage were evaluated via tissue biopsies. Exposure to bile evoked significant mast cell degranulation and leukocyte accumulation, and the red blood cell velocity (VRBC) and the diameter of the postcapillary venules (VD) increased significantly. The tissue ATP content and constitutive nitric oxide synthase activity decreased, while the inducible nitric oxide synthase activity increased significantly as compared with the control values. 7-NI treatment significantly exacerbated the mucosal mast cell degranulation and tissue damage. In contrast, PC pretreatment reversed the bile-induced ATP depletion, the inducible nitric oxide synthase and myeloperoxidase activity increases, and the mast cell degranulation. CONCLUSIONS: The neuronal nitric oxide synthase--mast cell axis plays an important role in the esophageal mucosal defense system. Systemic PC pretreatment affords effective protection through ameliorating the bile-induced ATP depletion and secondary inflammatory reaction.