Ventilatory compensation of the alkaline tide during digestion in the snake Boa constrictor

The increased metabolic rate during digestion is associated with changes in arterial acid-base parameters that are caused by gastric acid secretion (the 'alkaline tide'). Net transfer of HCl to the stomach lumen causes an increase in plasma HCO3- levels, but arterial pH does not change because of a ventilatory compensation that counters the metabolic alkalosis. It seems, therefore, that ventilation is controlled to preserve pH and not P-CO2, during the postprandial period. To investigate this possibility, we determined arterial acid-base parameters and the metabolic response to digestion in the snake Boa constrictor, where gastric acid secretion was inhibited pharmacologically by oral administration of omeprazole. The increase in oxygen consumption of omeprazole-treated snakes after ingestion of 30% of their own body mass was quantitatively similar to the response in untreated snakes, although the peak of the metabolic response occurred later (36 h versus 24 h). Untreated control animals exhibited a large increase in arterial plasma HCO3- concentration of approximately 12 mmol 1(-1), but arterial pH only increased by 0.12 pH units because of a simultaneous increase in arterial P-CO2 by about 10 mmHg. Omeprazole virtually abolished the changes in arterial pH and plasma HCO3- concentration during digestion and there was no increase in arterial P-CO2. The increased arterial P-CO2 during digestion is not caused, therefore, by the increased metabolism during digestion or a lower ventilatory responsiveness to ventilatory stimuli during a presumably relaxed state in digestion. Furthermore, the constant arterial P-CO2, in the absence of an alkaline tide, of omeprazole-treated snakes strongly suggests that pH rather than P-CO2 normally affects chemoreceptor activity and ventilatory drive.

Effects of temperature on lung and blood gases in the South American rattlesnake Crotalus durissus terrificus

The effects of temperature on lung and blood gases were measured in the South American rattlesnake (Crotalus durissus terrificus). Arterial blood and lung gas samples were obtained from chronically cannulated animals at 15, 25, and 35 degrees C. As expected for reptiles, arterial pH fell with increased temperature (0.018 U degrees C-1 between 15 and 25 degrees C and 0.011 U degrees C-1 between 25 and 35 degrees C) while lung gas PCO2 rose from 5.8 mmHg at 15 degrees C to 13.2 mmHg at 35 degrees C. Concurrently, lung gas PO2 declined from 132 mmHg at 15 degrees C to 120 mmHg at 35 degrees C, and arterial PO2 increased from 33 to 76 mmHg in that temperature range. Arterial haemoglobin O-2 saturation rose from 0.53 at 15 degrees C to 0.83 at 25 degrees C but became slightly reduced (0.77) with a further elevation of temperature to 35 degrees C. Arterial haemoglobin concentration increased from 1.96 to 2.53 mM between 15 and 35 degrees C, consistent with higher demands on oxygen delivery to tissues at elevated temperatures. Moreover, the substantial increase of haemoglobin O-2 saturation between 15 and 25 degrees C conforms to the idea that reduction of the central vascular right-to-left shunt (pulmonary bypass of systemic venous return) is associated with high metabolic demands. (C) 1998 Elsevier B.V. All rights reserved.

Structural insights into the catalytic mechanism of sphingomyelinases D and evolutionary relationship to glycerophosphodiester phosphodiesterases

Spider venom sphingomyelinases D catalyze the hydrolysis of sphingomyelin via an Mg2+ ion-dependent acid-base catalytic mechanism which involves two histidines. In the crystal structure of the sulfate free enzyme determined at 1.85 angstrom resolution, the metal ion is tetrahedrally coordinated instead of the trigonal-bipyramidal coordination observed in the sulfate bound form. The observed hyperpolarized state of His47 requires a revision of the previously suggested catalytic mechanism. Molecular modeling indicates that the fundamental structural features important for catalysis are fully conserved in both classes of SMases D and that the Class II SMases D contain an additional intra-chain disulphide bridge (Cys53-Cys201). Structural analysis suggests that the highly homologous enzyme from Loxosceles bonetti is unable to hydrolyze sphingomyelin due to the 95G1y -> Asn and 134Pro -> Glu mutations that modify the local charge and hydrophobicity of the interfacial face. Structural and sequence comparisons confirm the evolutionary relationship between sphingomyelinases D and the glicerophosphodiester phosphoesterases which utilize a similar catalytic mechanism. (c) 2006 Elsevier B.V. All rights reserved.

Structural basis for metal ion coordination and the catalytic mechanism of sphingomyelinases D

Sphingomyelinases D (SMases D) from Loxosceles spider venom are the principal toxins responsible for the manifestation of dermonecrosis, intravascular hemolysis, and acute renal failure, which can result in death. These enzymes catalyze the hydrolysis of sphingomyelin, resulting in the formation of ceramide 1-phosphate and choline or the hydrolysis of lysophosphatidyl choline, generating the lipid mediator lysophosphatidic acid. This report represents the first crystal structure of a member of the sphingomyelinase D family from Loxosceles laeta (SMase I), which has been determined at 1.75-angstrom resolution using the quick cryo-soaking technique and phases obtained from a single iodine derivative and data collected from a conventional rotating anode x-ray source. SMase I folds as an (alpha/beta)(8) barrel, the interfacial and catalytic sites encompass hydrophobic loops and a negatively charged surface. Substrate binding and/or the transition state are stabilized by a Mg2+ ion, which is coordinated by Glu(32), Asp(34), Asp(91), and solvent molecules. In the proposed acid base catalytic mechanism, His(12) and His(47) play key roles and are supported by a network of hydrogen bonds between Asp(34), Asp(52), Trp(230), Asp(233), and Asn(252).

Desenvolvimento de metodologia simplificada para análise de hexametilenotetramina (hmt) em medicamentos contendo corantes em sua formulação

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Theoretical study of MgO(001) surfaces: Pure, doped with Fe, Ca, and Al, and with and without adsorbed water

Ab initio calculations of large cluster models have been performed in order to study water adsorption at the five-fold coordinated adsorption site on pure Mg(001) and MgO(001) surfaces doped with Fe, Ca, and Al. The geometric parameters of the adsorbed water molecule have been optimized preparatory to analysis of binding energies, charge transfer, preferential sites of interaction, and bonding distances. We have used Mulliken population analysis methods in order to analyze charge distributions and the direction of charge transfer. We have also investigated energy gaps, HOMO energies, and SCF orbital energies as well as the acid-base properties of our cluster model. Numerical results are compared, where possible, with experiment and interpreted in the framework of various analytical models. (C) 2001 John Wiley & Sons, Inc.

Control of breathing in anuran amphibians

The primary role of the respiratory system is to ensure adequate tissue oxygenation, eliminate carbon dioxide and help to regulate acid-base status. To maintain this homeostasis, amphibians possess an array of receptors located at peripheral and central chemoreceptive sites that sense respiration-related variables in both internal and external environments. As in mammals, input from these receptors is integrated at central rhythmogenic and pattern-forming elements in the medulla in a manner that meets the demands determined by the environment within the constraints of the behavior and breathing pattern of the animal. Also as in mammals, while outputs from areas in the midbrain may modulate respiration directly, they do not play a significant role in the production of the normal respiratory rhythm. However, despite these similarities, the breathing patterns of the two classes are different: mammals maintain homeostasis of arterial blood gases through rhythmic and continuous breathing, whereas amphibians display an intermittent pattern of aerial respiration. While the latter is also often rhythmic, it allows a degree of fluctuation in key respiratory variables that has led some to suggest that control is not as tight in these animals. In this review we will focus specifically on recent advances in studies of the control of ventilation in anuran amphibians. This is the group of amphibians that has attracted the most recent attention from respiratory physiologists. (c) 2006 Elsevier B.V. All rights reserved.

ANTAGONISM OF THE MYOTOXIC EFFECTS OF BOTHROPS-JARARACUSSU VENOM AND BOTHROPSTOXIN BY POLYANIONS

The effects of heparin and other polyanions on the myotoxicity of Bothrops jararacussu venom and purified bothropstoxin (BthTX) were investigated. The release rate of creatine kinase (CK) from isolated extensor digitorum longus muscle and the plasma CK activity of mice were used to quantify the results. The myotoxic effects of B. jararacussu venom or BthTX were inhibited by preincubation of these agents with one of the following: a heterogeneous heparin preparation (designated 'heparin'), low mol. wt heparin (H-4500) or dextran sulfates (DS-8000 and DS-500,000). Non-sulfated dextran (D-40,000) and two chondroitin sulfates were ineffective. The antimyotoxic effects of the polyanions are ascribed to their forming inactive acid-base complexes with the basic myotoxins of Bothrops venoms. Gel-filtration experiments in Sephadex provided direct evidence for complex formation between heparin and BthTX. Intravenous (i.v.) administration of H-4500 or DS-8000 opposed the increase in plasma CK activity induced by a subsequent i.m. injection of venom or BthTX. In contrast, pretreatment with i.v. heparin or DS-500,000 enhanced the venom-induced increase in plasma CK activity. This effect was not observed (1) when the animals were treated with a polyvalent antivenom, which inhibits the coagulation and local stasis induced by Bothrops venoms, and (2) when BthTX, which has no thrombotic or hemorrhagic properties, was the myotoxic agent. The potentiation of the venom-induced increase in plasma CK activity by heparin and DS-500,000 is ascribed to improved washout of the CK released from damaged fibers, because of the anticoagulant properties of the drugs.

Relation between ambient humidity and ionic conductivity of poly(thionaphtheneindole): Behaviour as an amperometric humidity sensor

The electrical characteristics of oxidized poly(thionaphtheneindole) were investigated as a function of ambient relative humidity (r.h.). The current flowing through a pressed pellet of material between two massive gold electrodes plotted against voltage gives a wave-shaped curve with a halfwave potential at V = similar to 3 V. The current recorded at 4 V (plateau of the wave) is a sigmoidal function of r.h, with the inflexion point at similar to 60%. An interpretation of these findings is given, based on the influence of water on the dielectric constant of the material and on acid-base equilibrium between poly(thionaphtheneindole) and water, from which protons are produced. The behaviour of poly (thionaphtheneindole) as the active component of an amperometric humidity sensor is also reported.

Factors affecting metabolic and electrolyte changes after reperfusion in liver transplantation

Background. The metabolic and electrolyte changes were evaluated after various durations of cold and warm ischemia times to correlate ASA status with hemodynamic changes that may affect the severity of the reperfusion syndrome.Patients and methods. Sixty-one patients who underwent liver transplantation (OLT) were monitored by arterial pH, PaO2, PaCO2, HCO3, BE, K+, Ca2+, Na+, GL, and serial Ht at three specific times: after the skin incision (baseline), 10 minutes before reperfusion (T-2), and 10 minutes after reperfusion (T-3). Changes in metabolic parameters were correlated with ASA status, hemodynamic changes, time of OLT, as well as cold and warm ischemia times.Results. The pH in ASA IV patients was significantly lower at T-1 and T-3, and PCO2 higher in ASA V at T-1. A significant correlation was observed between pH, PaCO2, HCO3 BE, Na+, Ca2+, and glucose with the phase of the procedure. The pH and HCO3 decreased significantly from T-1 and T-2, increasing during T-3. Ca2+ fell from T-1 to T-2 increasing in T-3. Mean glucose and sodium levels increase from T-1 to T-3. Mean BE dropped from T-1 to T-2 and increased at T-3 without a significant correlation between the metabolic parameters in any phase of the study and the cold or warm ischemia times. Patients with a high ASA status showed an increased risk for cardiovascular collapse after reperfusion.Conclusions. Patients with advanced ASA status are more prone to metabolic and acid-base disturbances during reperfusion, without any relation to the cold or warm ischemia times. High ASA status shows an increased risk for cardiovascular collapse after reperfusion.

Rhodamine B-containing silica films from TEOS precursor: Substrate surface effects detected by photoluminescence

This work presents the study of substrate surface effects on rhodamine B-containing silica films obtained from TEOS (tetraethylorthosilicate) acid hydrolysis. Soda-lime glass substrates were treated with basic solution under different reaction times and temperatures. Rhodamine B-containing silica films were deposited on pre-treated substrates by the spin-coating method. The substrate surface directly affects film morphology and homogeneity. The films are formed by packed silica spheres which protect the dye against acid-base attack. Luminescence spectra present shifts on the dye emission maximum as expected for different pH values on the substrate surface depending on the alkaline treatment. (c) 2006 Elsevier B.V. All rights reserved.

Atividade microbiana em solos, influenciada por resíduos de algodão e torta de mamona

Microbial activity constitutes a good indicator of soil quality, and is influenced by the addition of carbon in the system serving as a substrate for microorganisms that increase their activity and release of CO2, comprising the edaphic respiration of the soil. The objective of this study was to evaluate the microbial activity in different soil types with the addition of cake press of castor bean and cotton textile residue. The study was conducted in a greenhouse at the headquarters of Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) Cotton in randomized block design in 4 x 3 factorial arrangement with four replications. At predetermined intervals of 4 days, the containers were opened and the solution of NaOH titrated with HCl 2N in the presence of acid/base indicator phenolphthalein. After reading, the same amount of NaOH was added and the containers were closed again. The difference between the amounts of acid needed to neutralize the sodium hydroxide in a control container and the treatments was equivalent to the amount of carbon dioxide produced by soil microorganisms. It was found that the residues influenced the microbial activity in different soil types, especially in the initial determinations, presenting themselves as good sources for mineralization and nutrient supply, the castor bean proportionating higher cumulative release of CO2 by microorganisms.

Metabolic acidosis in healthy mules under general anaesthesia with halothane

Objective To report the severe metabolic acidosis identified in a group of 11 healthy mules anaesthetized with halothane for castration.Study design Data generated from a prospective study.Animals Eleven mules aged 2.5-8 years, weighing 230-315 kg and 11 horses aged 1.5-3.5 years, weighing 315-480 kg.Methods Animals were anaesthetized for castration as part of an electroencephalographic study. Preanaesthetic medication was acepromazine (0.03 mg kg(-1)) administered through a preplaced jugular venous catheter. Anaesthesia was induced 30-90 minutes later with intravenous thiopental (10 mg kg(-1)). After orotracheal intubation, anaesthesia was maintained with halothane vaporised in oxygen. The animals' lungs were ventilated to maintain the end-tidal CO(2) concentration between 3.9 and 4.5 kPa (29-34 mmHg). Anaesthetic monitoring included invasive blood pressure measurement via the auricular artery (mules) and submandibular branch of the facial artery (horses). Arterial blood gas samples were drawn from these catheters at three time points during surgery and pH, PaCO(2), base excess (ecf) and HCO(3)(-) were measured. Values were compared between groups using a Mann-Whitney test. p was taken as <0.05. Results are reported as median (range).Results PaCO(2) did not differ between groups but pH was significantly lower in mules [7.178 (7.00-7.29)] compared to horses [7.367 (7.24-7.43)] (p = 0.0002). HCO(3)(-) values were significantly lower in the mules [16.6 (13.0-22.3) mM] compared to horses [23.7 (20.9-23.7) mM] (p = 0.0001), whilst base excess (ecf) was significantly more negative in the mules [-11.4 (-1.27 to -16) mM] compared to horses [-1.3 (-5.8 to +2.4) mM] (p = 0.0004).Conclusion and clinical relevance This study demonstrated severe metabolic acidosis in healthy mules, which may have prompted intervention with drug therapies in a clinical arena. It is probable that the acidosis existed prior to anaesthesia and caused by diet, but other possible causes are considered.

The workload and plasma ion concentration in a training match session of high-goal (elite) polo ponies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

O papel dos rins no equilíbrio ácido-básico em cães submetidos aos efeitos do halotano e hipercapnia

In eighteen dogs, the effects of halothane (0,75% and 1,5%) associated with a normo and hypercapnia (PaCO2 from 30 to 80 mmHg) on acid-base balance were studied. Determinations of creatine clearance, urinary flow, urinary acid excretion, and urinary ammonium excretion were made. Based on the results, it is concluded that halothane associated with hypercapnia decreases the glomerular filtration rate, the urinary flow, the urinary pH and the urinary bicarbonate and sodium excretion, increases the plasmatic bicarbonate concentration, the bicarbonate reabsorbed, the urinary acid excretion and the urinary ammonium excretion, but does not alter the base excess.