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Biomedical subjects

D Johnson

Publications and source records attributed to D Johnson.

At least 487 records · Page 27Linked to original sources
PubMed1990

Analysis of the substrate binding sites of human galactosyltransferase by protein engineering.

An expression vector, pIN-GT, encoding the soluble form of beta 1,4-galactosyltransferase (GT) has been constructed from human GT cDNAs and the pIN-III-ompA2 expression vector. Escherichia coli strain SB221 harboring the pIN-GT plasmid produces and secretes a fusion protein consisting of the ompA signal and GT. The expression of GT was detected by assaying enzymatic activity as well as by Western blotting using anti-GT antibodies. The recombinant GT was purified to homogeneity by N-acetylglucosamine-Sepharose affinity chromatography. The NH2-terminal peptide sequence of purified GT confirmed the cleavage site of the fusion protein by bacterial signal peptidase. This expression system was utilized to produce mutant forms of GT in order to identify specific amino acids involved in substrate binding sites. Photoaffinity labeling of GT with UDP-galactose analog, 4-azido-2-nitrophenyluridylylpyrophosphate (ANUP), followed by cyanogen bromide (CNBr) cleavage revealed that ANUP bound to a fragment of GT composed of amino acid residues from Asp276 to Met328. Within this peptide segment, Tyr284, Tyr287, Tyr309, Trp310 and Trp312 were separately substituted into Gly and Tyr287 into Phe by site-directed mutagenesis. Enzymatic activity assay showed drastic reduction of the activity in all of the mutants except that Tyr287----Phe remained as active as wild-type GT. Kinetic studies of the mutated GT showed that Tyr284, Tyr309 and Trp310 are critically involved in the N-acetyglucosamine binding and Tyr309 is involved in UDP-galactose binding as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Halothane inhibits hypoxic pulmonary vasoconstriction in the presence of cyclooxygenase blockade.

Using an isolated lung the effects of halothane on hypoxic pulmonary vasoconstriction (HPV) were studied in the presence of cyclooxygenase blockade. The pulmonary vasculature can be divided into arterial, middle and venous segment resistances. Analysis of the vascular pressure-flow relationship further separates resistance into a flow dependent resistance (1/slope) and a zero-flow pressure intercept (PCRIT). We ventilated six lobes with control (35 per cent O2) and hypoxic (three per cent O2) gas mixtures with the addition of either 0, 0.5, 1.0, or 2.0 per cent halothane. We found that after addition of indomethacin (5 mg.kg-1), ventilation with three per cent O2 increased total resistance by 87 per cent over baseline with the increase primarily in the middle vascular segment. During normoxic ventilation PCRIT was 7.9 cm H2O and this increased significantly with hypoxia to 11.5 cm H2O). Only 2.0 per cent halothane blocked the increases in middle segment resistance and in PCRIT. We conclude that following cyclooxygenase blockade, halothane inhibits HPV by acting on middle segment vessels.

Animals↗
PubMed1990

Identification of IgE-positive cells and mast cells in frozen sections of multiple sclerosis brains.

There is evidence that nervous system mast cells may be involved in the pathogenesis of experimental demyelinating diseases, and that their involvement may be mediated by IgE. In order to examine the possible relevance of these observations to human demyelinating diseases, we have histologically and immunocytochemically examined multiple sclerosis (MS) and control brains for the presence of mast cells and IgE. Using a highly specific antiserum, we found IgE-positive cells in MS brains, but not in controls. IgE-positive cells could be detected in all regions of MS lesions, but were far more frequent in areas of active infiltration. Immunopositive staining was only observed when sections were pretreated with a methanolic peroxide solution, suggesting that the IgE was cytoplasmic. Positive cells typically exhibited plasma cell morphology. Mast cells were identified using chloroacetate esterase (CAE) staining, and we were able to confirm previous reports of an increased association of mast cells with MS lesions. Mast cells were seen in 7/14 MS brains compared with 1/8 controls. They were most commonly observed in demyelinated areas, but were also seen in association with infiltrate. Mast cells and IgE-positive cells were also observed in areas of perivascular infiltration in other inflammatory central nervous system diseases (subacute sclerosing panencephalitis, herpes encephalitis). Mast cells may represent a route for infiltrating cells to enter the brain in inflammatory disorders.

Brain↗
PubMed1990

Acute inhalation toxicity of soman and sarin in baboons.

Adult baboons (Papio sp.; 8-12 kg) were anesthesized with sodium pentobarbital (20 mg/kg iv). The animals were instrumented for measurement of mean blood pressure (MBP), pulmonary artery pressure (PAP), ECG, arterial and mixed venous blood gases, lung volumes, lung pressures, and efferent phrenic nerve activity. Bronchoalveolar lavage (BAL) was performed. Studies were done prior to exposure, at intervals during the first 4 hr postexposure, and at 4 and 28 days after exposure. Control animals received a sham exposure to 2-propanol (N = 5). Soman (pinacolyl methylphosphonofluoridate) at 13.14 micrograms/kg (2 X LD50) was vaporized into the upper airway in a second group of animals (N = 5), and sarin (isopropyl methylphosphonofluoride) 30 micrograms/kg (2 X LD50) was vaporized into a third group of animals (N = 4). Controls showed no change in any parameter either immediately after diluent exposure or during the monitoring period. Soman and sarin produced a decline in MBP and bradyarrhythmias that were reversed with atropine. Apnea occurred in all soman- and sarin-exposed animals within 5 min postexposure, and was associated with absence of phrenic nerve signal. Ventilation was mechanically supported until the animal could maintain normal arterial blood gases during spontaneous breathing. BAL studies revealed an increase in total white cell population and neutrophils at 4 hr in all three groups. There were signs of impaired hemodynamics and persistent lung injury for 4 days that resolved by 28 days after exposure. In conclusion, inhalation of soman and sarin in the baboon is associated with cardiac arrhythmias, development of apnea, and a significant decrease in MBP. Inhalation exposure also resulted in a persistent influx of neutrophils and hypoxemia.

Administration, Inhalation↗
PubMed1990

Atrial and ventricular arrhythmias in asymptomatic active elderly subjects: correlation with left atrial size and left ventricular mass.

Elderly normal subjects have an increased prevalence of cardiac arrhythmias compared with young and middle-aged subjects. The objective of this study was to test the hypothesis that the incidence and complexity of atrial and ventricular arrhythmias may be related to either left atrial enlargement or to increased left ventricular mass, respectively. From 146 asymptomatic volunteers older than 60 years, 86 subjects were considered to be free of cardiovascular abnormalities and had adequate M-mode echocardiograms and 24-hour ambulatory electrocardiograms. The mean age was 72 +/- 7 years, with a range of 60 to 96 years. There were 37 men and 49 women. During 1415 +/- 73 minutes of ambulatory electrocardiography, the average heart rate was 72 +/- 8 beats/min in men and 76 +/- 6 beats/min in women (p less than 0.05). Atrial arrhythmias were present in 64 subjects (74%); the frequency and complexity of these arrhythmias correlated with left atrial size (p less than 0.01). Ventricular arrhythmias were present in 55 subjects (64%); the frequency and complexity of ventricular arrhythmias did not correlate with left ventricular mass index. These results suggest that left atrial dilatation, a normal development in healthy elderly subjects, plays a significant role in the pathophysiology of the increased incidence of atrial arrhythmias. Increased left ventricular mass, which also occurs normally in the aging heart, is not, on the other hand, associated with an increased frequency and/or complexity of ventricular arrhythmias.

Aged↗
PubMed1990

Long-term neurophysiologic outcome after neonatal extracorporeal membrane oxygenation.

We examined clinical and neurophysiologic measures in 10 children 4 to 9 years after neonatal extracorporeal membrane oxygenation. Electroencephalograms did not correlate with clinical or other neurophysiologic measures of interhemispheric asymmetry. By ultrasound imaging, the right internal carotid artery velocity was approximately 62% of that on the left, and right internal carotid flow was reduced by 74% (p less than or equal to 0.01), whereas an age-matched control group showed no differences. A decrease in the amplitude of the long-latency auditory and somatosensory evoked potentials was noted over the right hemisphere after left-sided stimulation compared with the left hemispheric potentials after right-sided stimulation (p less than or equal to 0.005). No significant differences in hemispheric symmetry were noted in the amplitudes for wave V of the auditory brain-stem response or in the P30 component of the middle-latency auditory evoked potentials. Likewise, latency measures of the evoked potentials were symmetric. We conclude that (1) neonatal extracorporeal membrane oxygenation is associated with long-lasting decreased right internal carotid blood flow with compensatory increased flow through the left carotid system and (2) there is a consistent reduction in the amplitude of right hemispheric long-latency evoked potentials. These latter findings may reflect redirected cerebral blood flow patterns after extracorporeal membrane oxygenation.

Blood Flow Velocity↗
PubMed1990

The effects of halothane in hypoxic pulmonary vasoconstriction.

Human and animal experiments have not consistently shown halothane to inhibit hypoxic pulmonary vasoconstriction (HPV). The authors used a canine lung lobe perfused in situ to more precisely characterize the effects of halothane on HPV. The pulmonary vasculature can be divided into inflow, middle, and outflow segments by sequentially occluding the lobar inflow and outflow of blood. The lobes were ventilated with four different gas mixtures (normoxia, hypoxia, normoxia/halothane, hypoxia/halothane) and measured inflow, outflow, and middle segment (Rm) resistances using this stop-flow technique. All values are shown as means +/- standard deviation. The authors found that hypoxia increased Rm from normoxia values of .006 +/- .005 cmH2O.ml-1.min-1 to .025 +/- .008 cmH2O.ml-1.min-1 (P less than 0.05). During hypoxia/halothane Rm returned to .005 +/- .004 cmH2O.ml-1.min-1. The relationship between pressure and flow (P-Q) for the lobes for each gas mixture was also determined. The slopes of the P-Q lines by linear regression were all similar. The zero-flow pressure intercepts of the P-Q lines for normoxia (3.2 +/- .9 cmH2O) and hypoxia (4.4 +/- 1.1 cmH2O) were significantly decreased after the administration of halothane (1.7 +/- 1.0 cmH2O and 2.6 +/- 1.0 cmH2O, respectively). Since the zero-flow intercept likely reflects the tone at alveolar vessel level, the authors conclude that halothane inhibits HPV by decreasing the tone in the middle vascular segment.

Animals↗
PubMed1990

Effects of prostaglandins and the autonomic nervous system on the vasodilatory properties of nitroglycerin in conscious dogs.

This study was designed to assess the respective roles of prostaglandins and the autonomic nervous system in the responses to nitroglycerin (NTG) in conscious dogs. In vivo, NTG (1, 10, and 100 micrograms/kg i.v.) induced dose-dependent decreases in blood pressure and increases in heart rate and cardiac output. Coronary and carotid blood flows increased simultaneously, whereas responses in renal blood flow were biphasic, i.e., an initial decrease was followed by an increase above control at 10 and 100 micrograms/kg. NTG responses were not changed by indomethacin but were affected by chlorisondamine alone or in combination with indomethacin; tachycardia was abolished, and increases in cardiac output after 10 and 100 micrograms/kg were reduced by 26 and 32%, respectively, after ganglionic blockade and by 19 and 32%, respectively, after chlorisondamine plus indomethacin. In addition, increases in carotid blood flow in doses of 100 micrograms/kg were reduced by 88% after chlorisondamine and 83% after chlorisondamine plus indomethacin. Finally, in the presence of chlorisondamine plus indomethacin, NTG induced a more pronounced hypotension associated with a more pronounced renal vasodilation at the highest dose. Independent of indomethacin pretreatment, NTG in vitro induced a dose-dependent relaxation of the carotid, coronary, and renal arteries. Depending on the vascular bed, the reflex and local controls of circulation are affected differently by NTG.

Animals↗
PubMed1990

Defective oxidation of pristanic acid by fibroblasts from patients with disorders in propionic acid metabolism.

The alpha-methyl fatty acid, pristanic acid (2, 6, 10, 14 tetramethylpentadecanoic acid) is oxidised rapidly by normal skin fibroblasts in culture to CO2 and to water-soluble metabolites. The latter are secreted into the culture medium. Fibroblasts from patients with propionyl CoA carboxylase, and to a lesser extent from patients with methylmalonyl CoA mutase defects, show reductions in the amount of CO2 released, although the production of water-soluble metabolites is not affected. Our data indicate that propionic acid is produced from pristanic acid, and ultimately from its immediate precursor phytanic acid. As phytanic and pristanic acids are significant components of diets rich in ruminant fats, it is likely that they may contribute to the accumulation of propionate and its metabolites in disorders of propionate metabolism.

Amino Acid Metabolism, Inborn Errors↗
PubMed1990

The relationship between changing answers and performance on multiple-choice nursing examinations.

The purpose of this study was to investigate answer changing among undergraduate nursing students on multiple choice examinations. The sample included 284 students enrolled in the upper division of a baccalaureate nursing program. Answer sheets were examined for erasures to determine the number and direction of changes made. The results of the study indicated that most students changed at least one answer. Analysis of the data indicated that there was a significant difference between changing from wrong to right versus changing from right to wrong. About 55.3% gained points as a result of changing answers while only 18.3% lost points.

Adult↗
PubMed1990

A comparative study of straight chain and branched chain fatty acid oxidation in skin fibroblasts from patients with peroxisomal disorders.

The beta-oxidation of stearic acid and of alpha- and gamma-methyl isoprenoid-derived fatty acids (pristanic and tetramethylheptadecanoic acids, respectively) was investigated in normal skin fibroblasts and in fibroblasts from patients with inherited defects in peroxisomal biogenesis. Stearic acid beta-oxidation by normal fibroblast homogenates was several-fold greater compared to the oxidation of the two branched chain fatty acids. The effect of phosphatidylcholine, alpha-cyclodextrin, and bovine serum albumin on the three activities suggests that different enzymes are involved in the beta-oxidation of straight chain and branched chain fatty acids. Homogenates of fibroblasts from patients with a deficiency in peroxisomes (Zellweger syndrome and infantile Refsum's disease) showed a normal ability to beta-oxidize stearic acid, but the oxidation of pristanic and tetramethylheptadecanoic acid was decreased. Concomitantly, 14CO2 production from the branched chain fatty acids by Zellweger fibroblasts in culture (but not from stearic acid) was greatly diminished. The Zellweger fibroblasts also showed a marked reduction in the amount of water-soluble metabolites from the radiolabeled branched chain fatty acids that are released into the culture medium. The data presented indicate that the oxidation of alpha- and gamma-methyl isoprenoid-derived fatty acids takes place largely in peroxisomes in human skin fibroblasts.

Adrenoleukodystrophy↗
PubMed1990

[Atrial tachycardia and nodal ventricular fibers].

The paper presents the results of direct operations for nodal tachycardias. Electrophysiological studies and open heart operations revealed that extranodal formations were implicated in the tachycardias. In particular it was found that some of them were located in front of the atrioventricular node closer to the fibrous angle (Type A) in some cases or closer to the base of the coronary sinus (Type B) in the others. From 1983 to 1989 the author performed 107 operations for nodal, the so-called borderline tachycardias (Type A) and 7 operations for Type B, as well as 4 for mixed tachycardia. No patient died, the negative results amounted to 8%. The incidence of complete transversal block was 3%. The long-term results indicated recurrent tachycardias in 13% of the cases, all the cases being noted in Type A.

Adolescent↗
PubMed1990

[New aspects of assessment of physical development of children and adolescents by preventive examinations].

The results of the examinations of a representative cross-section were used as the basis for bringing up to date the standard values and ranges of variability of the body measurements of newborns according to gestational age, of head circumference up to the 3rd year and of body height and weight from 0-18 years. Tables and somatograms were also drawn up for the evaluation of body weight in relation to specific types of build, and standard values for skinfold thickness and total body fat were worked out in order to permit a biologically meaningful assessment of the physical development and nutritional status of children and adolescents. Alongside the description of the individual stages in the development of selected characteristics of maturation used in assessing sexual maturity, percentiles for the average age on reaching each of these stages of development will be available, together with a new series of photographs of breast, pubes and genital development.

Anthropometry↗
PubMed1990

Phenotypes and functions of lymphocytes in congenital toxoplasmosis.

Comparisons of lymphocyte surface phenotypes and functions were made among 25 pediatric patients with congenital toxoplasmosis (ages 1 month to 5 years) and 24 uninfected babies, a baby with postnatally acquired infection, and 6 uninfected, 7 recently infected, and 6 chronically infected adults. Percentages of lymphocytes with B1, T11, T3, T4, T8, T6, B4, Ia, NKH phenotypes and T4 to T8 ratios of infected and uninfected babies were the same (p greater than 0.05). Lymphocytes from congenitally infected babies had lower blastogenic responses (mean stimulation index [SI] = 5) to Toxoplasma lysate antigens (TLA) than lymphocytes from adult control groups with recent and chronic infection (Mean SIs = 32, 72; p less than 0.001). Compared to infected adults, congenitally infected children had similar or greater responses to concanavalin A (mean SIs = 94; 118, 76, p greater than 0.05) and in mixed leukocyte culture (mean SIs = 63; 22, 26, p greater than 0.05). For symptomatic babies, low blastogenic response to TLA correlated with more severe disease at presentation (p = 0.002). Lymphocyte blastogenic responses to TLA were increased for most children when they were older than 15 months, but responses remained less than adult levels for 9 of the 17 older children studied. There was no correlation between concomitant serum pyrimethamine levels and lymphocyte blastogenic responses to TLA. Pyrimethamine and sulfonamide treatment in vitro and in vivo did not alter lymphocyte response to TLA. Lymphocytes from congenitally infected babies failed to produce either gamma interferon or Interleukin 2 when cultured with TLA. In contrast, they produced these lymphokines when cultured with concanavalin A or phytohemagglutinin. Specific deficits in cell-mediated immune responses to TLA may account for the significant organ damage that occurs in infants and children with congenital toxoplasmosis.

Adult↗