[The two sides of mild hypothermia].
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Humans↗
Biomedical subjects
A Bacher
Publications and source records attributed to A Bacher.
Riluzole does not attenuate increases in hippocampal glutamate concentrations in a rabbit model of repeated transient global cerebral ischemia.
UNLABELLED: The aim of the present study was to examine the ability of riluzole to inhibit glutamate release during episodes of transient global cerebral ischemia. New Zealand White rabbits (n = 36) were anesthetized with halothane and mechanically ventilated to maintain normocarbia. Microdialysis catheters were inserted bilaterally into the dorsal hippocampus and perfused with artificial cerebrospinal fluid at 2 microL/min. Animals were randomly assigned to control, hypothermia (30 degrees C), or riluzole (2 or 8 mg/kg; R2 and R8) groups. Two episodes of transient global cerebral ischemia (each lasting 10 min) were produced by inflating the pneumatic tourniquet combined with induced hypotension. Dialysate was collected throughout the periischemic period, and glutamate concentrations were determined by using high-performance liquid chromatography. Peak levels were compared by using the Kruskal-Wallis test. Glutamate concentrations significantly increased by twofold to fourfold during the second ischemic period for the control, R2, and R8 groups. Glutamate concentrations in the hypothermic group were significantly lower than those in the other three groups and remained at baseline levels during the entire experiment. This study demonstrates that the sodium channel blocker riluzole does not inhibit ischemia-induced glutamate accumulation. The previously reported neuroprotective ability of riluzole may be caused by mechanisms other than the presynaptic inhibition of glutamate release during ischemia. IMPLICATIONS: Glutamate, an excitatory neurotransmitter, is released in excessive amounts during brain ischemia and may result in neuronal injury and death. Riluzole, a neuronal sodium channel blocker, has neuroprotective properties in some animal models of brain ischemia, possibly because of its ability to inhibit the release of glutamate from synaptic vesicles. However, this microdialysis study failed to demonstrate any attenuation of glutamate release during transient global ischemia after the administration of either 2 mg/kg or 8 mg/kg of riluzole.
Animals↗
Effects of temperature on cerebral tissue oxygen tension, carbon dioxide tension, and pH during transient global ischemia in rabbits.
BACKGROUND: A decrease in brain temperature (Tbrain) causes a decrease in the cerebral metabolic rate for oxygen (CMRO2) and provides potent neuroprotection against ischemic damage. In the present study, the effects of mild to moderate hypothermia on cerebral tissue oxygen tension (PO2 brain), carbon dioxide tension (PCO2 brain), and pH (pHbrain) were monitored during short episodes of global cerebral ischemia. METHODS: After approval by the Animal Care and Use Committee, 10 New Zealand white rabbits were anesthetized (1% halothane in air) and mechanical ventilation was adjusted to maintain the arterial carbon dioxide tension at 35 mmHg (alpha-stat). A sensor to measure PO2 brain, PCO2 brain, pHbrain, and Tbrain was inserted into the brain through a burr hole in the skull. Tbrain was adjusted to 38 degrees C, 34.4 degrees C, and 29.4 degrees C in a random sequence in each animal. PO2 brain, PCO2brain, and pHbrain (all variables are reported at the actual Tbrain) were recorded every 10 s during a 5-min baseline, 3 min of cerebral ischemia induced by inflation of a neck tourniquet, and 10 min of reperfusion at each level of Tbrain. Analysis of variance and Dunnett's test were used for statistical analysis. Data are presented as means +/- SD. RESULTS: During ischemia, PO2 brain decreased from 56 +/- 3 to 33 +/- 2 mmHg at 38 degrees C, from 58 +/- 3 to 32 +/- 3 mmHg at 34.4 degrees C, and from 51 +/- 2 to 32 +/- 2 mmHg at 29.4 degrees C (p = NS). PCO2 brain increased by 6.7 +/- 2 mmHg at 38 degrees C, by 5.1 +/- 1.4 mmHg at 34.4 degrees C, and by 2.3 +/- 0.8 mmHg at 29.4 degrees C. pHbrain inversely followed the trend of PCO2 brain. CONCLUSIONS: The attenuated increase in PCO2 brain during hypothermic ischemia results from the reduced CMRO2. The similar decrease in PO2 brain at all temperature levels indicates that despite the reduction in CMRO2, PO2 brain is no better preserved during brief episodes of hypothermic ischemia than during normothermic ischemia.
Analysis of Variance↗
Serial determinations of cerebral water content by magnetic resonance imaging after an infusion of hypertonic saline.
OBJECTIVE: To determine regional cerebral water content in vivo by magnetic resonance imaging (MRI) after the administration of 7.5% saline in brain-lesioned rabbits. DESIGN: Randomized, controlled, intervention trial. SETTING: University animal laboratory. SUBJECTS: Eighteen male New Zealand white rabbits, randomly assigned to one of three groups. INTERVENTIONS: The animals were anesthetized (1% halothane), intubated, and mechanically ventilated to maintain end-tidal CO2 tension between 30 and 35 mm Hg (4 and 4.7 kPa). Arterial and central venous catheters were inserted and arterial blood samples were serially obtained during the experiment. Serum osmolality was measured. A cryogenic cerebral lesion was produced by pouring liquid nitrogen for 1 min into a funnel placed on the intact skull over the right hemisphere. One group of animals received 20 mL of 7.5% saline intravenously 150 mins after the cerebral lesion was generated (7.5% saline group, n = 7). A second group of animals received the same volume of 0.9% saline intravenously (0.9% saline group, n = 7). In a third group of animals (control group, n = 4) no lesion was created and no fluid administered. MEASUREMENTS AND MAIN RESULTS: Five spin-echo T2-weighted MRIs of the brain were acquired at 90 mins (Baseline 1), 120 mins (Baseline 2), 150 mins (Infusion), 180 mins (Infusion + 30 mins), and 210 mins (Infusion + 60 mins) after the generation of the cerebral lesion. In the control group, two scans separated by a time interval of 120 mins were performed. The percent changes in signal intensity between the first and the four following scans of a coronal slice of the central region were determined. Analysis of variance and the Mann-Whitney U test were used for statistical analysis. Data are presented as mean +/- SD; p < .05 was considered significant. Serum osmolality increased significantly from 308 +/- 13 mosm/L to 349 +/- 19 mosm/L after the infusion of 20 mL of 7.5% saline, but did not change after the administration of 0.9% saline. Signal intensity in the area between the caudal edge of the core of the lesion and the basal ganglia was 9 +/- 8% higher on the injured side than in the corresponding area on the contralateral side (p < .05). Compared with Baseline 1, signal intensity at Infusion + 60 mins decreased by 26.3 +/- 13.7% in the 7.5% saline group, whereas it decreased by 10.4 +/- 8.6% in the 0.9% saline group (p < .05 between groups). Signal intensity decreased only slightly and nonsignificantly by 0.6 +/- 4.4% between the two scans in the control group. CONCLUSIONS: The administration of a 7.5% saline solution causes a prompt and substantial decrease in cerebral water content as assessed by spin-echo T2-weighted MRI. Magnetic resonance imaging offers the opportunity for repeated, noninvasive in vivo determinations of cerebral water content.
Animals↗
Three-dimensional analysis of cleft palate topology in newborn infants with reference to the cranial skeleton.
OBJECTIVE: To describe a method of determining the three-dimensional topology of the palatal crest relative to a reproducible anthropomorphic coordinate system in newborn infants with unilateral cleft palate. For this purpose, physical models of the maxilla and face were analyzed by computer morphometry. DESIGN: The study was limited to infants referred to the craniofacial center during the first 11 days after birth. SETTING: The study was performed at a craniofacial center servicing a large geographic area. PARTICIPANTS: The method was applied to 12 infants with unilateral cleft lip, alveolus, and palate (eight patients with left-side clefts and four with right-side clefts). MAIN OUTCOME MEASURES: The three-dimensional topology of the palatal crest referenced to an anthropometric coordinate system was the primary outcome measure. The anthropometric reference system is defined by the tragus points and the midpoint of a line connecting the endocanthia. RESULTS: The topology of the maxillary crests of the patients was characterized by considerable variability. The center of the premaxilla as defined by the attachment of the frenulum was frequently displaced by several millimeters from the midsagittal plane. The displacement was to the left in infants with right-side clefts and to the right in infants with left-side clefts. The premaxilla can be rotated by more than 30 degrees relative to the normal position. No significant retroposition of the minor segment as determined by the location of the tuber points was found. Several morphometric anomalies were found to be correlated linearly. CONCLUSIONS: We propose that the morphologic deviations are in part caused by the neuromotor activity of the tongue and of the interrupted M. orbicularis oris. The data can serve as the starting point for a longitudinal study of craniofacial development in children with cleft palate and for studies on the efficacy of different therapeutic approaches.
Alveolar Process↗
The 1.25 A crystal structure of sepiapterin reductase reveals its binding mode to pterins and brain neurotransmitters.
Sepiapterin reductase catalyses the last steps in the biosynthesis of tetrahydrobiopterin, the essential co-factor of aromatic amino acid hydroxylases and nitric oxide synthases. We have determined the crystal structure of mouse sepiapterin reductase by multiple isomorphous replacement at a resolution of 1.25 A in its ternary complex with oxaloacetate and NADP. The homodimeric structure reveals a single-domain alpha/beta-fold with a central four-helix bundle connecting two seven-stranded parallel beta-sheets, each sandwiched between two arrays of three helices. Ternary complexes with the substrate sepiapterin or the product tetrahydrobiopterin were studied. Each subunit contains a specific aspartate anchor (Asp258) for pterin-substrates, which positions the substrate side chain C1'-carbonyl group near Tyr171 OH and NADP C4'N. The catalytic mechanism of SR appears to consist of a NADPH-dependent proton transfer from Tyr171 to the substrate C1' and C2' carbonyl functions accompanied by stereospecific side chain isomerization. Complex structures with the inhibitor N-acetyl serotonin show the indoleamine bound such that both reductase and isomerase activity for pterins is inhibited, but reaction with a variety of carbonyl compounds is possible. The complex structure with N-acetyl serotonin suggests the possibility for a highly specific feedback regulatory mechanism between the formation of indoleamines and pteridines in vivo.
Alcohol Oxidoreductases↗
Retrobiosynthetic NMR studies with 13C-labeled glucose. Formation of gallic acid in plants and fungi.
The biosynthesis of gallic acid was studied in cultures of the fungus Phycomyces blakesleeanus and in leaves of the tree Rhus typhina. Fungal cultures were grown with [1-13C]glucose or with a mixture of unlabeled glucose and [U-13C6]glucose. Young leaves of R. typhina were kept in an incubation chamber and were supplied with a solution containing a mixture of unlabeled glucose and [U-13C6]glucose via the leaf stem. Isotope distributions in isolated gallic acid and aromatic amino acids were analyzed by one-dimensional 1H and 13C NMR spectroscopy. A quantitative analysis of the complex isotopomer composition of metabolites was obtained by deconvolution of the 13C13C coupling multiplets using numerical simulation methods. This approach required the accurate analysis of heavy isotope chemical shift effects in a variety of different isotopomers and the analysis of long range 13C13C coupling constants. The resulting isotopomer patterns were interpreted using a retrobiosynthetic approach based on a comparison between the isotopomer patterns of gallic acid and tyrosine. The data show that both in the fungus and in the plant all carbon atoms of gallic acid are biosynthetically equivalent to carbon atoms of shikimate. Notably, the carboxylic group of gallic acid is derived from the carboxylic group of an early intermediate of the shikimate pathway and not from the side chain of phenylalanine or tyrosine. It follows that the committed precursor of gallic acid is an intermediate of the shikimate pathway prior to prephenate or arogenate, most probably 5-dehydroshikimate. A formation of gallic acid via phenylalanine, the lignin precursor, caffeic acid, or 3,4, 5-trihydroxycinnamic acid can be ruled out as major pathways in the fungus and in young leaves of R. typhina. The incorporation of uniformly 13C-labeled glucose followed by quantitative NMR analysis of isotopomer patterns is suggested as a general method for biosynthetic studies. As shown by the plant experiment, this approach is also applicable to systems with low incorporation rates.
Carbon Isotopes↗
Terpenoid biosynthesis from 1-deoxy-D-xylulose in higher plants by intramolecular skeletal rearrangement.
The incorporation of [1-13C]- and [2,3,4,5-13C4]1-deoxy-D-xylulose into beta-carotene, lutein, phytol, and sitosterol in a cell culture of Catharanthus roseus was analyzed by NMR spectroscopy. The labeling patterns of the isoprene precursors, isopentenyl pyrophosphate and dimethylallyl pyrophosphate, were obtained from the terpenes by a retrobiosynthetic approach. 13C Enrichment and 13C13C coupling patterns showed conclusively that 1-deoxy-D-xylulose and not mevalonate is the predominant isoprenoid precursor of phytol, beta-carotene, and lutein. Label from 1-deoxyxylulose was also diverted to phytosterols to a minor extent (6% relative to carotene and phytol formation). The data demonstrate that the formation of isopentenyl pyrophosphate from pentulose occurs strictly by an intramolecular rearrangement process.
Cells, Cultured↗
Studies on the NusB protein of Escherichia coli--expression and determination of secondary-structure elements by multinuclear NMR spectroscopy.
The product of the nusB gene of Escherichia coli modulates the efficiency of transcription termination at nut (N utilization) sites of various bacterial and bacteriophage lambda genes. Similar control mechanisms operate in eukaryotic viruses (e.g. human immunodeficiency virus). A recombinant strain of E. coli producing relatively large amounts of NusB protein (about 10% of cell protein) was constructed. The protein could be purified with high yield by anion-exchange chromatography followed by gel-permeation chromatography. The protein is a monomer of 15.6 kDa as shown by analytical ultracentrifugation. Structural studies were performed using protein samples labelled with 15N, 13C and 2H in various combinations. Heteronuclear three-dimensional triple-resonance NMR experiments combined with a semi-automatic assignment procedure yielded the sequential assignment of the 1H, 13C and 15N backbone resonances. Based on experimentally derived scalar couplings, chemical-shift values, amide-exchange data, and a semiquantitative interpretation of NOE data, the secondary structure of NusB has classified as alpha helical, comprising seven alpha helices.
Amino Acid Sequence↗
Analysis of a chemical plant defense mechanism in grasses.
In the Gramineae, the cyclic hydroxamic acids 2,4-dihydroxy-1, 4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1, 4-benzoxazin-3-one (DIMBOA) form part of the defense against insects and microbial pathogens. Five genes, Bx1 through Bx5, are required for DIBOA biosynthesis in maize. The functions of these five genes, clustered on chromosome 4, were demonstrated in vitro. Bx1 encodes a tryptophan synthase alpha homolog that catalyzes the formation of indole for the production of secondary metabolites rather than tryptophan, thereby defining the branch point from primary to secondary metabolism. Bx2 through Bx5 encode cytochrome P450-dependent monooxygenases that catalyze four consecutive hydroxylations and one ring expansion to form the highly oxidized DIBOA.
Benzoxazines↗
Tracer studies with crude U-13C-lipid mixtures. Biosynthesis of the lipase inhibitor lipstatin.
The biosynthesis of the pancreatic lipase inhibitor lipstatin was investigated by fermentation experiments using cultures of Streptomyces toxytricini, which were supplied with soybean oil and a crude mixture of U-13C-lipids obtained from algal biomass cultured with 13CO2. Lipstatin was analyzed by one- and two-dimensional NMR spectroscopy. 13C total correlation spectroscopy and INADEQUATE experiments show that two fatty acid fragments containing 14 and 8 carbon atoms, respectively, are incorporated en bloc into lipstatin. The 14-carbon fragment is preferentially derived from the unsaturated fatty acid fraction, as shown by an experiment with hydrogenated U-13C-lipid mixture, which is conducive to labeling of the 8-carbon moiety but not of the 14-carbon moiety. The data indicate that the lipstatin molecule can be assembled by Claisen condensation of octanoyl-CoA with 3-hydroxy-delta5,8-tetradecanoyl-CoA obtained by beta oxidation of linoleic acid. The formation of lipstatin from acetate units by a polyketide-type pathway is ruled out conclusively by these data. The data show that surprisingly clear labeling patterns can be obtained in studies with crude, universally 13C-labeled precursor mixtures that are proffered together with a large excess of unlabeled material. One- and two-dimensional 13C total correlation spectroscopy analyses are suggested as elegant methods for the delineation of contiguously 13C-labeled biosynthetic blocks.
Enzyme Inhibitors↗
Biosynthesis of riboflavin: 3,4-dihydroxy-2-butanone-4-phosphate synthase.
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Candida↗
Biosynthesis of riboflavin: GTP cyclohydrolase II, deaminase, and reductase.
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Bacillus subtilis↗
Biosynthesis of riboflavin: lumazine synthase and riboflavin synthase.
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Bacillus subtilis↗
Sevoflurane or halothane anesthesia: can we tell the difference?
UNLABELLED: This study was performed to evaluate the ability of anesthesiologists to differentiate between sevoflurane, a newer, more expensive anesthetic, and halothane. A total of 113 assessments were made by 36 anesthesiologists on 58 children, aged 6 mo to 6 yr, scheduled for bilateral myringotomy and tube placement. All patients received midazolam (0.5 mg/kg per os) approximately 30 min before the induction of anesthesia. Sevoflurane or halothane was randomly selected for anesthetic induction and maintenance. The anesthesiologists, who were unaware of the anesthetic being used, were asked to identify the anesthetic based on clinical signs and to assess the quality of induction, speed of induction, and speed of emergence using a visual analog scale (VAS; minimum score = 0, maximum score = 100). The anesthesiologists correctly identified the anesthetic only 56.6% of the time. This was not significantly different from the 50% that would result from random guessing (P = 0.08). Further, there were no significant differences in VAS scores between the two groups. This study suggests that in premedicated pediatric patients undergoing brief surgical procedures, anesthesiologists cannot correctly differentiate between sevoflurane and halothane. The lack of significant differences in VAS scores suggests that the speed of induction, the speed of emergence, and the quality of induction are similar under these clinical conditions. Any purported benefits of sevoflurane seem to be of minor consequence under the circumstances studied. IMPLICATIONS: When the anesthetic halothane or sevoflurane is administered in a blind, randomized fashion, anesthesiologists could not reliably identify which drug was being used to anesthetize children for a brief surgical procedure. These results suggest that the differences between the two drugs in clinical practice are small and may not justify the additional cost of sevoflurane.
Anesthesia, Inhalation↗
Lamotrigine inhibits extracellular glutamate accumulation during transient global cerebral ischemia in rabbits.
BACKGROUND: During cerebral ischemia, an influx of Na+ may be partially responsible for the release of the excitatory amino acid glutamate. When glutamate is released in excessive concentrations during ischemia, it may become neurotoxic. The ability of the Na+ channel blocker lamotrigine to inhibit glutamate release during episodes of transient global cerebral ischemia was investigated. METHODS: After approval was given by the animal care and use committee, 24 New Zealand white rabbits were randomly assigned to one of four groups each containing six animals (control, L20, L50, and a hypothermic group). After anesthesia (1% halothane) was induced, the tracheas were intubated and the lungs mechanically ventilated before microdialysis probes were placed in the hippocampus. Ninety minutes before the onset of ischemia, either 20 or 50 mg/kg lamotrigine was administered intravenously (in the L20 and L50 groups). Esophageal temperature was maintained at 38 degrees C in the control. L20 and L50 groups, whereas the animals in the hypothermic group were cooled to 30 degrees C. Two 10-min periods of cerebral ischemia, separated by a 90-min interval, were generated by inflating a neck tourniquet. High-performance liquid chromatography was used to determine the glutamate concentration in the microdialysate. Analysis of variance and Dunnett's test were used for statistical analysis. Data are presented as means +/- SD. RESULTS: During the first ischemic period, glutamate concentration increased only slightly from baseline. A significant increase was observed during the second ischemic period for the control (sixfold) and the L20 (threefold) groups. Glutamate concentrations in the L50 and the hypothermic groups were significantly lower than in the other two groups and remained at the baseline level during the entire experiment. CONCLUSIONS: This study shows that the Na+ channel blocker lamotrigine is effective in inhibiting extracellular glutamate accumulation during transient global cerebral ischemia. This attenuation of ischemia-induced glutamate release may explain the previously reported neuroprotective properties of Na+ channel blockers.
Animals↗
Effects of pentoxifylline on hemodynamics and oxygenation in septic and nonseptic patients.
OBJECTIVE: To evaluate the effects of pentoxifylline on hemodynamics and systemic oxygenation in septic and nonseptic critically ill patients. DESIGN: Prospective clinical investigation. SETTING: Intensive care unit (ICU) of a university hospital. PATIENTS: Nineteen critically ill patients were included in the study 1 to 4 days after their admission to the ICU. A systemic inflammatory response syndrome was present in 12 patients, fulfilling at least two of the American College of Chest Physicians/ Society of Critical Care Medicine Consensus Conference criteria. The other seven patients did not fulfill these criteria and were classified as nonseptic. INTERVENTIONS: All patients were mechanically ventilated. The dosage of catecholamines was kept constant during the entire study period and at least during 15 mins before the start of the study. In both study groups, pulmonary and radial artery catheters were inserted and 5 mg/kg of pentoxifylline (diluted in 300 mL of physiologic saline) was intravenously administered over a period of 180 mins at a rate of 100 mL/hr. MEASUREMENTS AND MAIN RESULTS: Hemodynamic variables, oxygen transport (DO2), oxygen uptake (VO2), and oxygen extraction ratio were determined before pentoxifylline, after 2.5 mg/kg of pentoxifylline, after 5 mg/kg of pentoxifylline, and 60 mins after the termination of pentoxifylline. Repeated-measures analysis of variance and Mann-Whitney test were used for statistical analysis. At baseline, there were significant differences between the septic and the nonseptic groups in mean pulmonary arterial pressure (septic: 31 +/- 5 mm Hg; nonseptic: 26 +/- 7 mm Hg, p < .05), and pulmonary vascular resistance index (PVRI) (septic: 344 +/- 121 dyne.sec/ cm5.m2; nonseptic: 233 +/- 100 dyne.sec/cm5.m2, p < .05). In the septic group, significant increases in heart rate and cardiac index were observed. Systemic vascular resistance index and PVRI decreased. No significant changes in hemodynamic variables occurred in the nonseptic group. In both groups, DO2 and VO2 increased significantly, while oxygen extraction ratio remained unchanged. CONCLUSIONS: The administration of pentoxifylline to septic patients results in a significant improvement in hemodynamic performance compared with critically ill nonseptic patients. The better hemodynamic state is accompanied by an increase in DO2 and VO2 with unchanged oxygen extraction ratio.
Adult↗
Changes in oxygenation variables during progressive hypothermia in anesthetized patients.
Because deliberate hypothermia is becoming commonly used during neurosurgery, this study was performed to investigate the effects of a progressive reduction of body core temperature (T) on whole body oxygenation variables in patients undergoing elective intracranial surgery. In 13 patients (Hypothermic Group), T was reduced to 32.0 degrees C using convective-based surface cooling. In six patients (Control Group), T was maintained at 35.5 degrees C during the entire study period. The cardiac index (CI) was determined with a pulmonary artery catheter by thermodilution. Whole body oxygen delivery (DO2) was calculated from CI and arterial oxygen content. Whole body oxygen consumption (VO2), carbon dioxide production (VCO2), and energy expenditure (EE) were determined by ventilation gas analysis (indirect calorimetry). Mixed venous oxygen tension at 50% saturated hemoglobin (P50), and whole body oxygen extraction ratio (O2ER) were calculated. Repeated-measures analysis of variance and the Mann-Whitney test were used for statistical analysis. Data are expressed as means +/- SD. VO2 (from 100 +/- 13 to 77 +/- 11 ml.min-1.m-2), VCO2 (from 75 +/- 7 to 57 +/- 7 ml.min-1. m-2), EE (from 667 +/- 67 to 509 +/- 66 kcal.d-1.m-2), P50 (from 23.8 +/- 1.7 to 20 +/- 0.9 mm Hg), and O2ER (from 0.29 +/- 0.05 to 0.22 +/- 0.03%) decreased significantly in the Hypothermic Group between 35.5 and 32.0 degrees C (p < 0.05). None of these variables changed in the Control Group and at 32.0 degrees C VO2, VCO2, EE, P50, and O2ER were significantly lower in the Hypothermic Group than in the Control Group. DO2 remained unchanged in both groups. We conclude that progressive hypothermia in anesthetized patients reduces metabolic rate but does not change DO2. The significant decrease in O2ER may partly be related to a leftward shift of the oxyhemoglobin dissociation curve, as evidenced by the decrease in P50.
Aged↗