A acid-stable analogue of the 3-beta-D-ribofuranoside of Y-base. (1/745)

A cyclonucleoside analogue of Y(TU) riboside has been prepared and shown to be relatively stable in M-hydrochloric acid solution at room temperature.  (+info)

Experimental acid-aspiration pneumonia in the rabbit. A pathologic and morphometric study. (2/745)

Four anesthetized rabbits given intratracheal injections of hydrochloric acid, pH 1.5, 2 ml/kg, were killed 4 h later. A fifth rabbit was an untreated control. Each lung had a few red-brown patches of compression atelectasis. Microscopically, treated lungs had a severe exudative necrotizing bronchitis, bronchiolitis, and alveolitis. There was also intra-alveolar hemorrhage and edema. Electron microscopy showed folds, projections and focal swellings of type I cells lining affected alveoli. A morphometric study showed 69% of parenchyma to be normal, 26% edematous and 5% hemorrhagic. In the airways 58% of the epithelium was damaged.  (+info)

The magnitude of changes in guanidine-HCl unfolding m-values in the protein, iso-1-cytochrome c, depends upon the substructure containing the mutation. (3/745)

Hydrophilic to hydrophobic mutations have been made at 11 solvent exposed sites on the surface of iso-1-cytochrome c. Most of these mutations involve the replacement of lysine with methionine, which is nearly isosteric with lysine. Minimal perturbation to the native structure is expected, and this expectation is confirmed by infrared amide I spectroscopy. Guanidine hydrochloride denaturation studies demonstrate that these variants affect the magnitude of the m-value, the rate of change of free energy with respect to denaturant concentration, to different degrees. Changes in m-values are indicative of changes in the equilibrium folding mechanism of a protein. Decreases in m-values are normally thought to result either from an increased population of intermediates during unfolding or from a more compact denatured state. When cytochrome c is considered in terms of its thermodynamic substructures, the changes in the m-value for a given variant appear to depend upon the substructure in which the mutation is made. These data indicate that the relative stabilities and physical properties of substructures of cytochrome c play an important determining role in the equilibrium folding mechanism of this protein.  (+info)

Preferential acid-catalyzed hydrolysis of the formamide linkage of N'-formylkynurenine in frozen solution. (4/745)

Acid-catalyzed hydrolysis of the formamide linkage of N-acetyl-N'-formyl-L-kynurenineamide in frozen dilute hydrochloric acid solution followed first-order kinetics, yielding N-acetyl-L-kynurenineamide as the sole reaction product. The maximum rate of reaction in the frozen solution was found at around -7.5 degrees and approximated that of the reaction in liquid solution at 40 degrees. By freezing the dilute acid solution at -8 degrees the reaction was accelerated by 60 times compared with that in super-cooled liquid solution at the same temperature.  (+info)

Interference in the quantitation of methylated arsenic species in human urine. (5/745)

The aim of this paper is to report on the presence of chemical interferences in the quantitation of methylated arsenic species in human urine when using a method based on selective volatile arsine species generation, chromatographic separation, and hydride generation atomic absorption spectrometry (HGAAS) detection. An abnormal profile of methylated arsenic species characterized by the absence of the peak corresponding to dimethylarsinic acid (DMA) was observed in urine from some individuals exposed to arsenic via drinking water and living in rural communities of northwestern Argentina. The absence of this peak persisted even after the addition of known amounts of DMA to the samples. However, the DMA peak appeared after urine digestion with hydrochloric acid (2M). Samples showing interferences were provided by individuals who had mate consumption and coca-leaf chewing habits. Because the relative proportions of methylated arsenic species present in urine have been used to evaluate the efficiency of the methylation process, interferences in the formation or detection of methylarsines may cause underestimation of As exposure and also lead to erroneous conclusions about relative biomethylation efficiencies. Therefore, we recommend that urine samples should be digested with 2M HCl before performing speciation analysis using HGAA techniques. Further studies on the impact of this type of interferences on other arsenic speciation methods are also required.  (+info)

Larynx vs. esophagus as reflexogenic sites for acid-induced bronchoconstriction in dogs. (6/745)

Bronchoconstriction in asthmatic patients is frequently associated with gastroesophageal reflux. However, it is still unclear whether bronchoconstriction originates from the esophagus or from aspiration of the refluxate into the larynx and larger airway. We compared the effect of repeated esophageal and laryngeal instillations of HCl-pepsin (pH 1.0) on tracheal smooth muscle activity in eight anesthetized and artificially ventilated dogs. Saline was used as control. We used pressure in the cuff of an endotracheal tube (Pcuff) as a direct index of smooth muscle activity at the level of the larger airways controlled by vagal efferents. The Pcuff values of the first 60 s after instillations were averaged, and the difference from the baseline values was evaluated. Changes in Pcuff were significantly greater with laryngeal than with esophageal instillations (P = 0.0166). HCl-pepsin instillation into the larynx evoked greater responses than did saline (P = 0.00543), whereas no differences were detected with esophageal instillations. Repeated laryngeal exposure enhanced the responsiveness significantly (P < 0. 001). Our data indicate that the larynx is more important than the esophagus as a reflexogenic site for the elicitation of reflex bronchoconstriction in response to acidic solutions.  (+info)

Vagal esophageal receptors in anesthetized dogs: mechanical and chemical responsiveness. (7/745)

This study was performed to evaluate the characteristics of esophageal receptors in anesthetized and artificially ventilated dogs. The electrical activity of the esophageal afferents was recorded from the peripheral cut end of the cervical vagus nerve. A cuffed catheter was inserted into the esophagus at the level of the third tracheal ring and was used to establish the esophageal location of the endings. Most of the receptors were localized in the intrathoracic portion of the esophagus. The majority of the receptors studied (36 of 43) showed a slow adaptation to a maintained stretch of the esophageal wall. Vagal cooling blocked receptor activity at temperatures ranging from 3.5 to 25 degrees C. Twenty-eight of 43 receptors, including 4 rapidly adapting endings (RAR), were challenged with saline, HCl + pepsin (HCl-P; pH 1) and distilled water (8 ml, 37 degrees C). HCl-P solutions specifically stimulated only three receptors; saline or water did not. Five slowly adapting receptors and two RARs were also challenged with topically applied capsaicin; only one RAR was stimulated. To ascertain a possible effect of smooth muscle contraction, 17 receptors were tested with intravenous injections of ACh and/or asphyxia; only 4 were stimulated. These characteristics do not support an important reflexogenic role of the esophagus in response to chemical stimuli.  (+info)

Extracellular acidification induces human neutrophil activation. (8/745)

In the current work, we evaluated the effect of extracellular acidification on neutrophil physiology. Neutrophils suspended in bicarbonate-buffered RPMI 1640 medium adjusted to acidic pH values (pH 6.5-7.0) underwent: 1) a rapid transient increase in intracellular free calcium concentration levels; 2) an increase in the forward light scattering properties; and 3) the up-regulation of surface expression of CD18. By contrast, extracellular acidosis was unable to induce neither the production of H2O2 nor the release of myeloperoxidase. Acidic extracellular pH also modulated the functional profile of neutrophils in response to conventional agonists such as FMLP, precipiting immune complexes, and opsonized zymosan. It was found that not only calcium mobilization, shape change response, and up-regulation of CD18 expression but also production of H2O2 and release of myeloperoxidase were markedly enhanced in neutrophils stimulated in acidic pH medium. Moreover, extracellular acidosis significantly delayed neutrophil apoptosis and concomitantly extended neutrophil functional lifespan. Extracellular acidification induced an immediate and abrupt fall in the intracellular pH, which persisted over the 240-s analyzed. A similar abrupt drop in the intracellular pH was detected in cells suspended in bicarbonate-supplemented PBS but not in those suspended in bicarbonate-free PBS. A role for intracellular acidification in neutrophil activation is suggested by the fact that only neutrophils suspended in bicarbonate-buffered media (i.e., RPMI 1640 and bicarbonate-supplemented PBS) underwent significant shape changes in response to extracellular acidification. Together, our results support the notion that extracellular acidosis may intensify acute inflammatory responses by inducing neutrophil activation as well as by delaying spontaneous apoptosis and extending neutrophil functional lifespan.  (+info)