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Biomedical subjects

R J Stewart

Publications and source records attributed to R J Stewart.

At least 73 records · Page 4Linked to original sources
PubMed1993

Role of hiatal hernia in delaying acid clearance.

The aim of this study was to assess prospectively the relationship of a hiatal hernia to gastro-oesophageal reflux. Ninety five children with symptoms of gastro-oesophageal reflux in whom reflux was demonstrated radiologically were investigated. Oesophageal pH monitoring for 18 hours and endoscopy were performed in all patients. On the basis of radiology, patients were divided into those with hiatal hernia (n = 37) and those without (n = 58). Both groups had the same number of reflux episodes on pH monitoring. However, the median duration of the longest episode was significantly greater in the hiatal hernia group (30 min v 19 min), as was the number of reflux episodes longer than five minutes (5 v 4). The percentage with a pH < 4 just failed to be significantly different (13% v 8%). Hiatal hernia was also found to correlate with the presence of oesophagitis. The presence of a hiatal hernia delays the clearance of acid from the oesophagus and is associated with an increased incidence of oesophagitis.

Adolescent↗
PubMed1993

Synthesis of digoxigenin-labeled cRNA probes for nonisotopic in situ hybridization using reverse transcription polymerase chain reaction.

Nonisotopic methods of mRNA in situ hybridization have distinct advantages over isotopic techniques. Nonisotopically labeled probes are stable and nontoxic, have short detection times, demonstrate excellent spatial resolution of their signals and have sensitivities comparable to radiolabeled probes. We developed a simple method of generating nonisotopically labeled cRNA probes which is based on the reverse transcription polymerase chain reaction (RT-PCR) and used it to synthesize a panel of probes for various murine extracellular matrix genes. Engelbreth-Holm-Swarm (EHS) tumor RNA was reverse transcribed and PCR was used to amplify defined regions of multiple extracellular matrix protein genes from the resulting first strand cDNAs. Bacteriophage promoters which had been incorporated into the PCR products were then used to generate digoxigenin-conjugated antisense and sense cRNAs. The antisense probes were employed to detect the specific extracellular matrix protein mRNAs in the EHS tumor by in situ hybridization. This technique provides a rapid and efficient alternative to conventional transcription systems which use plasmid vectors for the synthesis of digoxigenin-labeled cRNA probes.

Animals↗
PubMed1992

Measurement of free radicals from smoke inhalation and oxygen exposure by spin trapping and ESR spectroscopy.

Research in smoke inhalation has established that free radicals are produced from gases released during combustion and these species impair lung function. Using spin traps and their adducts in an animal model free radicals were measured. Various hyperbaric oxygen regimens were tested in an attempt to attenuate pulmonary damage caused by free radical reactions. Our data demonstrated that persistent oxygen- and carbon-centered free radicals are detectable in intravascular fluids after smoke inhalation. The smoke inhalation model showed however, clearing of spin trap adducts one hour after smoke exposure. Other researchers have found that when 100% oxygen is given at 1 atmosphere absolute (ATA) for 1 h, free radicals were not detectable. However, oxygen given at 2.5 ATA does produce detectable free radicals. With continued exposure at this pressure, the levels of free radicals increase for up to 60 min. This study suggests that the level of free radical induced oxygen toxicity may be a function of oxygen pressure and duration of oxygen exposure.

Animals↗
PubMed1991

Identification and partial characterization of six members of the kinesin superfamily in Drosophila.

Recent evidence has suggested that the principal polypeptide component of the microtubule motor protein kinesin may be a member of an extended superfamily of related motor proteins. To gain insight into how large the kinesin superfamily might be and to begin determining the potential functions in which various superfamily members might participate, we identified and partially characterized six additional members of the Drosophila kinesin superfamily. Genes encoding these proteins were identified by using the polymerase chain reaction with degenerate primers corresponding to highly conserved regions of the kinesin heavy-chain motor domain. Partial sequencing of the six genes revealed that they encode proteins that are 40-60% identical to the motor domain of the kinesin heavy-chain sequence. The cytogenetic locations as well as the developmental and tissue-specific expression patterns have been determined. The data suggest that each of these six kinesin-like proteins may have functions in a wide variety of cell types and tissues.

Age Factors↗
PubMed1991

Histological changes following submucosal Teflon injection in the bladder.

Histological examination following subureteric Teflon injection was carried out on 32 ureters and four granulomatous polyps. When the Teflon was correctly placed in the submucosa it remained circumscribed and reflux was more likely to be corrected. If the Teflon was placed more deeply it became diffuse, caused a giant cell reaction, and was less likely to correct the reflux. The granulomatous polyps may represent a reaction to leakage of Teflon from the injection site.

Foreign-Body Reaction↗
PubMed1990

The kinesin-like ncd protein of Drosophila is a minus end-directed microtubule motor.

The Drosophila ncd gene is required for chromosome segregation during female meiosis. Previous analyses suggested that the ncd gene encoded a protein with sequence similarity to the kinesin motor domain, which suggested that, like kinesin, the ncd protein might be a plus end-directed microtubule motor. Here we describe the expression of ncd protein in E. coli and the initial characterization of the ncd protein's motor properties. The ncd protein is indeed a microtubule motor, but the polarity of movement is minus end directed. The ncd protein also has microtubule bundling activity. These findings limit possible models for the in vivo functions of the ncd protein and suggest that motor proteins with similar sequence can generate movement in opposite directions along a microtubule.

Animals↗
PubMed1990

Role of GTP hydrolysis in microtubule polymerization: evidence for a coupled hydrolysis mechanism.

The relationship between GTP hydrolysis and microtubule assembly has been investigated by using a rapid filtration method. Microtubules assembled from phosphocellulose-purified tubulin, double-labeled with [gamma-32P]- and [3H]GTP, were trapped and washed free of unbound nucleotide on glass fiber filters. The transient accumulation of microtubule-bound GTP predicted by uncoupled GTP hydrolysis models [Carlier & Pantaloni (1981) Biochemistry 20, 1918-1924; Carlier et al. (1987) Biochemistry 26, 4428-4437] during the rapid assembly of microtubules was not detectable under our experimental conditions. By calculating hypothetical time courses for the transient accumulation of microtubule-bound GTP, we demonstrate that microtubule-bound GTP would have been detectable even if the first-order rate constant for GTP hydrolysis were 4-5 times greater than the pseudo-first-order rate constant for tubulin subunit addition to microtubules. In a similar manner, we demonstrate that if GTP hydrolysis were uncoupled from microtubule assembly but were limited to the interface between GTP subunits and GDP subunits (uncoupled vectorial hydrolysis), then microtubule-bound GTP would have been detectable if GTP hydrolysis became uncoupled from microtubule assembly at less than 50 microM free tubulin, 5 times the steady-state tubulin concentration of our experimental conditions. In addition, during rapid microtubule assembly, we have not detected any microtubule-bound Pi, which has been proposed to form a stabilizing cap at the ends of microtubules [Carlier et al. (1988) Biochemistry 27, 3555-3559]. Also, several conditions that could be expected to increase the degree of potential uncoupling between GTP hydrolysis and microtubule assembly were examined, and no evidence of uncoupling was found. Our results are consistent with models that propose cooperative mechanisms that limit GTP hydrolysis to the terminal ring of tubulin subunits [e.g., O'Brien et al. (1987) Biochemistry 26, 4148-4156]. The results are also consistent with the hypothesis that a slow conformational change in tubulin subunits after GTP hydrolysis and Pi release occurs that results in destabilized microtubule ends when such subunits become exposed at the ends.

Animals↗
PubMed1990

Evidence that the head of kinesin is sufficient for force generation and motility in vitro.

Kinesin is a mechanochemical protein that converts the chemical energy in adenosine triphosphate into mechanical force for movement of cellular components along microtubules. The regions of the kinesin molecule responsible for generating movement were determined by studying the heavy chain of Drosophila kinesin, and its truncated forms, expressed in Escherichia coli. The results demonstrate that (i) kinesin heavy chain alone, without the light chains and other eukaryotic factors, is able to induce microtubule movement in vitro, and (ii) a fragment likely to contain only the kinesin head is also capable of inducing microtubule motility. Thus, the amino-terminal 450 amino acids of kinesin contain all the basic elements needed to convert chemical energy into mechanical force.

Adenosine Triphosphatases↗
PubMed1990

Dependence of the surface expression of the glycolipid cerebroside sulfate on its lipid environment: comparison of sphingomyelin and phosphatidylcholine.

The influence of the membrane lipid environment on the reactivity with antibody of the acidic glycolipid cerebroside sulfate (CBS) was examined by using a spin membrane immunoassay. Fewer antibodies in a polyclonal anti-CBS antiserum recognized the antigen in a bovine brain sphingomyelin/cholesterol (SM/CHOL) environment than in dipalmitoylphosphatidylcholine/cholesterol (DPPC/CHOL). Changes in the CBS ceramide group appeared to have less influence on antibody recognition of CBS in SM/CHOL than in DPPC/CHOL [Crook et al. (1986) Biochemistry 25, 7488-7494]. Although the fatty acid chain length of phosphatidylcholine strongly influences CBS recognition, the fatty acid chain length of sphingomyelin had only a moderate effect on CBS recognition and did not account for the decreased recognition in SM compared to in DPPC. Inhibition studies revealed that the antibodies which recognize CBS in SM/CHOL (S antibodies) form a population distinct from those which recognize CBS in DPPC/CHOL (P antibodies). The specificity of the P and S antibodies was examined further by comparing the efficacy of various substances, which share chemical features with the components of CBS in a SM/CHOL or DPPC/CHOL environment, to inhibit lysis of liposomes containing CBS. Intact CBS, cholesterol, and a phosphocholine lipid, at certain antigen densities, were required for optimal recognition of the antigen, especially by the P antibodies, suggesting that a complex of all three lipids in a multivalent array may be recognized by these antibodies. The S antibodies may recognize a smaller complex or monomers of CBS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The blood-testis barrier in experimental unilateral cryptorchidism.

Unilateral cryptorchidism was induced in Wistar rat pups within 48 h of birth. After a period of 150 days, the blood-testis barrier was evaluated in the cryptorchid and contralateral scrotal testis, using a lanthanum immersion technique. The barrier was demonstrated to be competent, with tracer confined to the basal and intermediate compartments.

Animals↗
PubMed1990

Fertility in experimental unilateral cryptorchidism.

Unilateral cryptorchidism was induced in Wistar rat pups within 48 hours of birth. Evaluation of fertility was subsequently assessed at 50, 100, and 150 days of age by paternity and daily sperm production. The descended scrotal testis was demonstrated to have a significantly diminished rate of sperm production at 150 days. Paternity studies failed to reflect this dysfunction, cryptorchid and sham-operated control animals having a 58% and 80% ability to produce offspring (P = .44).

Animals↗
PubMed1990

Effects of ibuprofen on pulmonary oedema in an animal smoke inhalation model.

The ability of ibuprofen to lower extravascular lung water significantly was examined in an animal smoke inhalation model. Adult New Zealand White rabbits weighing 3-5 kg were anaesthetized and intubated. They were then allowed to breathe cooled cotton smoke until the carboxyhaemoglobin (COHb) reached a level of 60 per cent or higher. Each ibuprofen-treated animal received a dose of 50 mg/kg either intraperitoneally or intravenously. Ibuprofen was administered to animals that received smoke inhalation alone and those that received smoke inhalation combined with a 10 per cent BSA partial skin thickness thermal injury. Control groups were established for both of the above-mentioned groups. Peak carboxyhaemoglobin levels as well as CO half-lives were not significantly different between ibuprofen-treated groups and the controls. Ibuprofen treatment resulted in significantly (P less than 0.05) decreased lung water in both smoke, and smoke plus thermal injury groups as compared to controls. These results suggest that ibuprofen promotes the reduction of early-onset lung water resulting from smoke inhalation injury alone or from smoke inhalation injury plus a thermal injury.

Animals↗
PubMed1990

Unilateral cryptorchidism: an animal model.

Unilateral division of the distal gubernaculum testis was performed, using hypothermic anaesthesia, in Wistar rats within 48 hours of birth. This resulted in ipsilateral abdominal testicular retention and contralateral descent. This model is suitable for the experimental study of congenital unilateral cryptorchidism and is presented in detail.

Animals↗
PubMed1990

Estimation of absolute numbers of damselfly nymphs (Odonata: Coenagrionidae) by dipper sampling in California rice fields with seasonal, spatial distributions and vegetation association.

Estimates of relative and absolute density in rice field populations of damselfly nymphs (predominantly Enallagma civile with few Ischnura denticollis) were compared using the regression method. An equation, X = Y divided by 0.0016, allows estimation of absolute density (X) from a relative density index (Y, dipper count). In the rice growing area of Fresno, California, nymphal population peaks appeared during June and August approaching 3-5 million per 0.405 ha (1 acre). Spatial distribution was theoretically represented fairly well by a negative-binomial distribution. The degree of clumping is one of overdispersed types; it is especially classified as a model of randomly distributed colonies with mean colony size fixed. Presence or absence of submerged vegetation markedly affected damselfly nymphal density but the biomass of submerged or emerged vegetation was not a significant factor.

Animals↗
PubMed1990

An enzyme histochemical study of large muscle fibres in the neonatal mouse.

Small clusters of extra large muscle fibres were identified in hindlimb muscles of neonatal mice (strain C57BL/10ScSn). At two days of age they had a significantly greater cross-sectional area than their normal counterparts (P less than 0.01). Fibre typing methods (NADH-tetrazolium reductase, ATPase and phosphorylase) classified them as 2A fast oxidative glycolytic (FOG fibres). The activity of NADH-tetrazolium reductase and the lysosomal enzymes beta-glucuronidase, acid phosphatase and dipeptidyl peptidase II were all elevated in the large fibres. Microsomal aminopeptidase (mAPP), a membrane-bound enzyme, also showed increased activity. The fibres are probably the mouse equivalent of the Wohlfart B fibres of the human fetus, with which comparison is made.

Aging↗