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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nitrate tolerance has been explained by 1) a direct loss of pharmacological effect due to reduced bioconversion and 2) an indirect effect due to activation of the renin/angiotensin system and counter-regulatory vasoconstriction. The sulfhydryl compound N-acetylcysteine (NAC) has been shown to attenuate and partly counteract tolerance to nitrates, and this effect has been attributed to a nitrate/sulfhydryl interaction and increased production of vasoactive intermediates. The effect of NAC on counter-regulatory mechanisms is, however, unknown. This study examined whether NAC modulates the function of the renin/angiotensin system in normal rats and in nitrate-tolerant healthy volunteers. Animal study: Conscious rats received NAC (5 mmol/kg/hr i.v., n = 8) or placebo (N-acetylserine, n = 8). Two hours of NAC infusion significantly reduced the pressor effect of angiotensin I (ANG I) by 39 +/- 14% (mean +/- SEM) and reduced angiotensin converting enzyme activity by 31% in plasma (N-acetylserine: 74 +/- 9 nmol/min/mg, NAC: 51 +/- 7) and 43% in kidney (N-acetylserine: 0.9 +/- 0.3, NAC: 0.5 +/- 0.1 nmol/min/mg protein) (P < .05). Clinical study: Isosorbide dinitrate (5 mg/hr) was infused into six male volunteers for 48 hr. NAC (2 g i.v. followed by 5 mg/kg/hr) was co-infused from 24 to 48 hr. Plasma angiotensin II (ANG II) increased during the first 24 hr of isosorbide dinitrate infusion and decreased from 28 +/- 4 to 14 +/- 2 ng/l after 2 hr of NAC infusion (P < .05). The results suggest that sulfhydryl supplementation modifies the function of the renin/angiotensin system in vivo, an effect probably mediated by inhibition of angiotensin converting enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:N-acetylcysteine inhibits angiotensin converting enzyme in vivo. 838 58

This work provides examples of some of the imaging capabilities of environmental scanning electron microscopy applied to easily charged samples relevant to particle analysis. Environmental SEM (also referred to as high pressure or low vacuum SEM) can address uncoated samples that are known to be difficult to image. Most of these specimens are difficult to image by conventional SEM even when coated with a conductive layer. Another area where environmental SEM is particularly applicable is for specimens not compatible with high vacuum, such as volatile specimens. Samples from which images were obtained that otherwise may not have been possible by conventional methods included fly ash particles on an oiled plastic membrane impactor substrate, a one micrometer diameter fiber mounted on the end of a wire, uranium oxide particles embedded in oil-bearing cellulose nitrate, teflon and polycarbonate filter materials with collected air particulate matter, polystyrene latex spheres on cellulosic filter paper, polystyrene latex spheres "loosely" sitting on a glass slide, and subsurface tracks in an etched nuclear track-etch detector. Surface charging problems experienced in high vacuum SEMs are virtually eliminated in the low vacuum SEM, extending imaging capabilities to samples previously difficult to use or incompatible with conventional methods.
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PMID:Environmental scanning electron microscope imaging examples related to particle analysis. 840 Apr 30

The use of IL-1 in humans is associated with dose-limiting toxicity which resembles that of TNF-alpha or IL-2. Activation of neutrophils is thought to contribute to the toxicity caused by these two cytokines. We studied the effect of IL-1 in vivo on changes in neutrophil numbers and neutrophil degranulation as well as on the formation of neutrophil agonists, such as complement activation products, and on levels of TNF, IL-6, IL-8, and nitrite/nitrate (as a measure of nitric oxide production). Six patients with metastatic melanoma were treated with 3 ng/kg recombinant human IL-1 beta daily. One hour after the start of the 30-min IL-1 infusion, which caused mild cardiovascular toxicity, plasma levels of IL-6 reached a peak of 25 +/- 9 ng/L (mean +/- SEM), IL-8 reached a peak of 311 +/- 100 ng/L at 2 h, and nitrite/nitrate peaked after 10 h to 89 +/- 27 mumol/L. IL-1 did not induce significant changes in plasma levels of TNF or of the complement activation products C3a and C4b/c. Although IL-1 induced neutrophilia, levels of elastase and lactoferrin did not change. The failure of IL-1 to degranulate neutrophils was confirmed in an ex vivo model with whole blood culture in which doses of up to 100 microgram/L IL-1 beta or IL-1 alpha failed to induce significant elastase or lactoferrin release, whereas TNF, tested as a positive control, was able to do so. These results demonstrate that, unlike TNF, IL-1 does not cause neutrophil degranulation in man, despite its ability to cause neutrophilia and the rapid release of IL-6, IL-8, and nitrite/nitrate.
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PMID:IL-1 beta does not cause neutrophil degranulation but does lead to IL-6, IL-8, and nitrite/nitrate release when used in patients with cancer. 859 89

Most microleakage studies involve quantitating the magnitude of movement of a tracer molecule through a gap between restorative materials and the wall of cavity preparations. The present microscopic study examined the migration of silver nitrate into the interface between dentin and five different dentin bonding agents used to restore class 5 cavities, in the absence of gap formation. Several different leakage patterns were seen, but they all indicated leakage within the hybrid layer when viewed by SEM. The ranking of microleakage from most to least was: All-Bond 2 > Suberbond C&B > Scotchbond Multi-Purpose > Clearfil Liner Bond System > Kuraray Experimental System, KB-200. To distinguish this special type of microleakage within the basal, porous region of the hybrid layer in the absence of gap formation, we propose the term nanoleakage.
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PMID:Nanoleakage: leakage within the hybrid layer. 870 Jul 62

Most adhesive interface studies have involved SEM demonstration of the penetration of adhesive resins into demineralized dentin surfaces with subsequent creation of hybrid layers. Nanoleakage is a term that describes the diffusion of small ions or molecules within the hybrid layer in the absence of gap formation. The present microscopic study examined the nanoleakage of the hybrid layer using a silver nitrate staining technique. Adhesive dentin sandwiches, which were immersed in a silver nitrate solution, were prepared for both SEM and TEM examination using both the Clearfil Liner Bond and All-Bond 2 adhesive systems. Both systems demonstrated silver accumulation within the hybrid layers. Clearfil Liner Bond System showed scattered silver particles at the bottom two-thirds of the hybrid layer by both SEM and TEM observation, whereas All-Bond 2 revealed stained fiber-like structures within the full thickness of the hybrid layer. To evaluate the quality of the hybrid layer, the utilization of tracer molecules such as silver nitrate that are detectable by both SEM and TEM is proposed. It is important to determine the location and morphology of these nanometer-sized porosities that may permit the hydrolysis of collagen fibers and degradation of adhesive monomers.
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PMID:Comparative SEM and TEM observations of nanoleakage within the hybrid layer. 870 Jul 85

Nicorandil is a hybrid of a nitrate and a potassium channel opener, and has a potent vasodilatory effect on coronary arteries. The effects of intracoronary injection of nicorandil on coronary circulation were examined in 12 adult patients with angiographically normal or near-normal left coronary arteries to determine the optimal dose of this agent. The intracoronary injection of nicorandil (up to 1 mg over 1 min) dilated left coronary artery segments in a dose-dependent manner, with no significant effects on systemic hemodynamic parameters. The percent increase in the epicardial coronary artery diameter with 1 mg nicorandil (31 +/- 5%, mean +/- SEM) was not significantly different from that with 0.3 mg sublingual nitroglycerin (39 +/- 5%). Coronary sinus venous oxygen saturation increased immediately after the intracoronary injection of 1 mg nicorandil, and then returned to the baseline level within 3 min. Neither arrhythmias nor conduction disturbances were observed. These results indicate that dilatation of the epicardial coronary artery was achieved with intracoronary nicorandil in a dose-dependent manner (up to 1 mg over 1 min) without any adverse effects in man, and the dilatory effect on coronary resistance vessels was of short duration.
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PMID:Effective and safe dose of intracoronary nicorandil in man. 874 63

Acute allograft rejection in patients after cardiac transplantation is associated with intense infiltration of inflammatory cells. It has been shown in animal studies that this inflammatory process is accompanied by an induction of nitric oxide syndrome (NOS) enzyme within the grafted organ. We sought to test the hypothesis that acute rejection in cardiac transplanted patients is associated with an increased production of nitric oxide. The radical nitric oxide is unstable in blood and oxidized to nitrite and nitrate; nitrate is secreted by the kidneys. Therefore, nitric oxide production was indirectly assessed by measuring urinary nitrate excretion. During a period of 1 yr, 86 consecutive patients after cardiac transplantation underwent one or more right heart biopsies (total 194) in order to assess for acute graft rejection. At the time of biopsies, urine was collected under sterile conditions. Urinary nitrate excretion was expressed as the ratio of nitrate to creatinine concentration in the urine (mumol/ mmol). Urinary nitrate excretion was 99.7 +/- 9.2 (mean +/- SEM) for patients without evidence of rejection, and tended to increase for patients with moderate/severe rejection (128 +/- 15.1). In a subgroup of patients who underwent several biopsies and showed different degrees of rejection (7 patients, 48 biopsies), urinary nitrate excretion significantly increased by about 99% during episodes of acute rejection. It is concluded that urinary nitrate excretion appears to be elevated in a subgroup of cardiac transplanted patients during episodes of acute rejection. Results are consistent with the hypothesis that acute graft rejection stimulates the production/release of nitric oxide. Because of a large inter- and intraindividual variation in urinary nitrate excretion, this parameter appears not to be suitable for diagnosis of acute rejection in cardiac transplanted patients.
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PMID:Urinary nitrate excretion is increased in cardiac transplanted patients with acute graft rejection. 882 70

Endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. We explored the effect of a continuous supply of human endothelial NO synthase (eNOS) on the blood pressure of spontaneously hypertensive rats (SHR) by somatic gene delivery. A DNA construct containing the human eNOS gene fused to the cytomegalovirus promoter/enhancer was injected into SHR through the tail vein. A single injection of the naked eNOS plasmid DNA caused a significant reduction of systemic blood pressure for 5 to 6 weeks in SHR, and the effect continued for up to 10 to 12 weeks after a second injection. The differences were significant from 2 to 12 weeks postinjections (n=6, P<.01). In a separate experiment, L-arginine, the substrate of eNOS, was supplied in drinking water at a concentration of 7.5 g/L for 11 weeks after eNOS gene delivery. A maximal blood pressure reduction of 21 mm Hg in SHR was observed with eNOS DNA compared with that of control SHR injected with vector DNA (181.9+/-1.46 versus 202.7+/-2.79 mm Hg, mean+/-SEM, n=6, P<.01). Human eNOS gene delivery induces significant increases in urinary and aortic cGMP levels and urinary and serum nitrite/nitrate content (P<.05), while no significant differences in body weight, heart rate, water intake, food consumption, or urine excretion were observed. These results indicate that somatic delivery of the human eNOS gene induces a prolonged reduction of high blood pressure and raises the potential of using eNOS gene therapy for hypertension and cardiovascular diseases.
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PMID:Prolonged reduction of high blood pressure with human nitric oxide synthase gene delivery. 931 9

Nitric oxide (NO) has been implicated in various aspects of physiological regulation in the gastrointestinal tract. Hence, measurement of luminal NO concentrations is of interest for studying physiological and pathophysiological alterations in NO generation; however, at present, no reliable measurement techniques are available. Here we describe novel approaches for measurement of NO concentrations directly in the gas phase of the stomach and colon in healthy subjects and patients. Studies were conducted in young healthy volunteers (n = 13), intensive care patients (n = 8) and patients undergoing gastroscopy (n = 8) or colonoscopy (n = 8). NO concentrations were measured by chemolumininescence detection in air obtained through a nasogastric tube, after inflation into the stomach of a defined volume of air, or directly in the air suctioned from the endoscope. The mean NO concentration obtained from the stomach of healthy volunteers studied under baseline conditions was 18.0 +/- 2.8 (SEM) p.p.m. Day-to-day reproducibility of NO measurements was high. Tube feeding with a nitrite- and nitrate-free feeding solution left gastric NO concentrations unchanged, but standardized bicycle exercise caused an approximately 30% decrease in NO levels. NO concentrations in intensive care patients were approximately 2 log cycles lower than in healthy volunteers. NO levels in the colon were similar to those in the stomach. We have described two readily applicable techniques for direct, uncontaminated measurement of NO concentrations in the lumen of the gastrointestinal tract. Our finding of a striking reduction in gastric NO concentrations in intensive care patients requires further study.
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PMID:Nitric oxide concentration in the gas phase of the gastrointestinal tract in man. 946 26

1. Basal release of nitric oxide from the vascular endothelium maintains a constant vasodilating tone. Impaired nitric oxide-mediated vasodilatation has been described in hypertension and atheromatous disease. Circulatory diseases account for considerable morbidity and almost half of all deaths in people over the age of 75 years. 2. We have therefore compared nitric oxide-dependent vasorelaxation in 12 healthy elderly subjects with 12 young volunteers matched for blood pressure, cholesterol and glucose, using forearm occlusion venous plethysmography combined with brachial artery infusions of the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA; 1, 2 and 4 mumol/min) with noradrenaline (60, 120 and 240 pmol/min) as a control vasoconstrictor. We also measured urinary nitrate excretion after a controlled 48 h low nitrate diet as an index of total body nitric oxide production and correlated these changes with forearm blood flow responses to L-NMMA and noradrenaline in both groups. 3. The mean age and blood pressure of the elderly subjects was 76 (range 66-82) years and 132/76 (SEM 4/3) mmHg respectively, while in the young these were 27 (20-35) years and 131/72 (4/3) mmHg respectively. L-NMMA and noradrenaline produced dose-dependent reductions in forearm blood flow in both groups. L-NMMA (4 mumol/min) produced less vasoconstriction in the elderly than in the young (-37.7 +/- 2.6 versus -48.3 +/- 4.2%; P = 0.017). The mean slope of the L-NMMA dose-response curves in the elderly was significantly less than the younger group (-35.2 +/- 3.1 versus -63.7 +/- 10.6; P = 0.041). Noradrenaline, 240 pmol/min, also produced less vasoconstriction in the elderly compared with the young (-22.8 +/- 2.9 versus -35.3 +/- 5.0%; P = 0.029) although the slopes of the dose-response curves did not differ significantly. 4. Urinary nitrate adjusted for creatinine clearance was also significantly higher in the younger group (460.6 +/- 97.7 versus 205.9 +/- 64.8 mumol/day; P = 0.042) and showed a significant correlation with the percentage change in forearm blood flow in response to the maximum dose of L-NMMA (r = 0.5, P = 0.046). 5. We conclude that nitric oxide-mediated vasodilatation in the forearm vascular bed is diminished in old age and this reflects a more generalized reduction in nitric oxide production (as measured by urinary nitrate) in the circulation of older people. The blunted response to noradrenaline points to a more generalized reduction in vascular reactivity in the elderly.
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PMID:Impaired nitric oxide-mediated vasodilatation and total body nitric oxide production in healthy old age. 949 88


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