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Biomedical subjects

R G Taylor

Publications and source records attributed to R G Taylor.

At least 55 records · Page 3Linked to original sources
PubMed1992

Altered neutrophil permeability following shock wave exposure in vitro.

Human neutrophils were exposed to varying numbers of shock waves using the Dornier XL-1 experimental lithotripter. Cellular changes were observed with as few as 60 shock waves generated with 20 KV at a frequency of one per second. A graded reduction in cell numbers and cell viability was observed up to 300 SW. With exposure to 140 SW or above a decrease in mean cell size occurred. When cells were shocked in the presence of adriamycin or after loading with fluorescein, flow cytometry revealed that influx of extracellular components and efflux of cytoplasmic components had occurred. An ultrastructural and functional analysis of cells exposed to 60 SW, where cellular disruption and loss of viability were minimal, revealed several types of cellular changes which may precede SW-induced cell death. Electron microscopic examination revealed in some cells a loss of staining intensity. Plasma membrane rupture and leakage of cytoplasmic components were occasionally evident. The adherence of shocked cells to glass, and the spreading of cells that had adhered, were also reduced. From these studies, it is concluded that cellular permeability and other vital cellular functions in neutrophils are perturbed by SW exposure.

Cell Adhesion↗
PubMed1992

Dentocutaneous fistula.

Chronic dental infection is the most common cause of draining sinus tracts of the face and neck. These lesions can be a diagnostic challenge to the clinician who is not familiar with dentocutaneous fistula. Diagnostic errors can result in multiple excisions, biopsies, and ineffective long-term antibiotic therapy. Patients may require excision of the fistula once the dental abscess has been successfully treated by root-canal therapy or extraction. Nine patients are reported.

Adolescent↗
PubMed1992

Platelet morphologic changes and fibrinogen receptor localization. Initial responses in ADP-activated human platelets.

Platelet exposure to agonists results in rapid morphologic changes paralleled by fibrinogen binding and platelet aggregation. The current study used standardized stereology in conjunction with immunogold electron microscopy to correlate the initial morphologic changes with fibrinogen receptor localization on the surfaces of ADP-activated human platelets. A 45% increase in platelet circumference was observed after 3 seconds of activation (P = 0.001). Virtually all of this increase was due to a 13-fold increase in projection membrane, and the projections observed by stereo microscopy at this time were mostly blunt. Both blunt and long projections also accounted for the increase in platelet-platelet contacts at 10 seconds of activation. Immunogold electron microscopy using the monoclonal antibodies P2 and AP-2 against the fibrinogen receptor, glycoprotein IIb/IIIa (GP IIb/IIIa), showed relatively equivalent immunogold densities on projections compared with cell body during 30 seconds of activation. The activation-dependent anti-GP IIb/IIIa monoclonal antibody, 7E3, showed an immunogold density 37% greater on projections compared with cell body (P = 0.0001). Colocalization studies using 7E3 with a polyclonal antifibrinogen antibody showed bound fibrinogen in close proximity to the GP IIb/IIIa localized by 7E3 on projections. These studies support an important role for platelet projections during the earliest stages of fibrinogen binding and ADP-induced aggregation.

Adenosine Diphosphate↗
PubMed1992

Analysis of human muscle contractility with a microcomputer-controlled stimulus and data acquisition system.

This report describes and assesses a technique to indirectly stimulate and quantify the human in vivo muscle response for clinical use. A method has been developed to isolate, stimulate, and record the flexor function of the first dorsal interosseus and first volar interosseus at the metacarpophalangeal (MCP) joint by stimulation of the ulnar nerve at the wrist. A microprocessor-based data acquisition and analysis system was built to deliver the electric stimulus and convert the muscle action potential (M-wave) and force measurements into digital form for analysis. To evaluate the technique, the twitch, paired twitch, and tetanic contractions were analyzed in 81 normal subjects. The tension developed by the youngest subjects (14 to 19 years old) was significantly less than the tension developed by subjects in the three older groups (20 to 34 years, 35 to 50 years, and 50 to 65 years); the tensions in the older groups were not significantly different from each other. Only minor gender differences were noted. This indicates that it is necessary to use age-group controls when looking for evidence of a muscle contractile abnormality in patients with neuromuscular disorders. posttetanic potentiation of the twitch was observed in all healthy subjects, and there was no evidence of an age or gender influence. The posttetanic increase in twitch tension was not associated with a prolongation of the twitch contraction time.

Action Potentials↗
PubMed1992

In vivo quantification of muscle contractility in humans: healthy subjects and patients with myotonic muscular dystrophy.

The purpose of this study was to use direct in vivo contractility measurements to assess muscle function in patients with myotonic muscular dystrophy (MMD). The tetanic and twitch responses and several time parameters of muscle contraction were obtained from nine MMD subjects and nine able-bodied, age-matched controls. After a routine nerve conduction study, in vivo contractility measurements were obtained by stimulating the ulnar nerve at the wrist and recording the isometric flexor function of the intrinsic muscles at the metacarpophalangeal joint of the index finger. A series of single stimuli, paired stimuli, and fused tetanic stimulations were generated during a 20-minute experimental protocol. A stable tetanus was produced at 50Hz for 1.2 seconds. M-wave and contractile data were recorded at 1,000Hz by digitization of the analog signal and storage by the microcomputer. The MMD patients were weaker than controls (p less than .05), as shown by the 39% reduction in tetanic tension and 57% reduction in twitch tension. The MMD patients also had a significant impairment in relaxing their muscles as shown by the 1,100% increase in half-relaxation time after contraction, even though there was no evidence of repetitive firing after cessation of stimulus. These data show that MMD patients exhibit failure of sarcolemmal activation, altered excitation-contraction coupling mechanisms, and failure of the contractile machinery. The myotonia is due in part, to some defect in the contractile machinery; it is not solely due to failure of sarcolemmal activation.

Adolescent↗
PubMed1991

Desmin is present in proliferating rat muscle satellite cells but not in bovine muscle satellite cells.

The presence of desmin was characterized in cultured rat and bovine satellite cells and its potential usefulness as a marker for identifying satellite cells in vitro was evaluated. In primary cultures, positive immunohistochemical staining for desmin and skeletal muscle myosin was observed in rat and bovine myotubes. A small number of mononucleated cells (20% of rat satellite cells and 5% of bovine satellite cells) were myosin-positive, indicative of post-mitotic differentiated myocytes. In bovine satellite cell cultures 13% of the mononucleated cells were desmin-positive, while 84% of the mononucleated cells in rat satellite cell cultures were desmin-positive. Rat satellite cell mass cultures and bovine satellite cell clonal density cultures were pulsed with 3H-thymidine, and autoradiographic data revealed that greater than 94% of dividing rat cells were desmin-positive, suggesting that desmin is synthesized in proliferating rat satellite cells. However, no desmin was seen in cells that incorporated labeled thymidine in bovine satellite cell clones. Analysis of clonal density cultures revealed that only 14% of the mononucleated cells in bovine satellite cell colonies were desmin-positive, whereas 98% of the cells in rat satellite cell colonies were desmin-positive. Fibroblast colonies from both species were desmin-negative. In order to further examine the relationship between satellite cell differentiation and desmin expression, 5-bromo-2'-deoxyuridine (BrdU) was added to culture medium at the time of plating to inhibit differentiation. Fusion was inhibited in rat and bovine cultures, and cells continued to divide. Very few desmin-positive cells were found in bovine cultures, but greater than 90% of the cells in rat cultures stained positive for desmin. The presence of desmin and sarcomeric myosin was also evaluated in regenerating rat tibialis anterior five days after bupivacaine injection. In regenerating areas of the muscle many desmin-positive cells were present, and only a few cells stained positive for skeletal muscle myosin. Application of desmin staining to rat satellite cell growth assays indicated that rat satellite cells cultured in serum-containing medium were contaminated with fibroblasts at levels that ranged from approximately 5% in 24 hr cultures to 15% in mature cultures. In defined medium 4 day cultures contain approximately 95% to 98% desmin-positive satellite cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Ultrasonic propagation in slurries.

Experimental measurements have been made of the ultrasonic velocity and attenuation in some simple suspensions of, mainly, silicon carbide in water and in ethylene glycol. These are compared with theoretical predictions based on a novel hydrodynamic model. Predicted ultrasonic velocities are in excellent agreement with the measured values. Predicted and measured ultrasonic attenuations do not agree as well. However, the suspensions give rise to excess attenuations rising to a few hundred nepers per metre and special experimental techniques were needed to measure ultrasonic properties. To predict attenuations to within, say, 20% for mixtures such as these is a major achievement.

Carbon↗
PubMed1991

Retinal haemorrhage in accidental head trauma in childhood.

Twenty-five children (age range 1.2-14.5 years) who sustained accidental head injury requiring admission to hospital were prospectively examined for evidence of retinal haemorrhage. In no case were retinal haemorrhages detected. It is suggested that accidental head injury seldom results in retinal haemorrhage and that the finding of retinal haemorrhage in a child with a head injury should prompt suspicion of abuse.

Accidents↗
PubMed1991

Localization of histidase to human chromosome region 12q22----q24.1 and mouse chromosome region 10C2----D1.

The human gene for histidase (histidine ammonia-lyase; HAL), the enzyme deficient in histidinemia, was assigned to human chromosome 12 by Southern blot analysis of human X mouse somatic cell hybrid DNA. The gene was sublocalized to region 12q22----q24.1 by in situ hybridization, using a human histidase cDNA. The homologous locus in the mouse (Hal) was mapped to region 10C2----D1 by in situ hybridization, using a cell line from a mouse homozygous for a 1.10 Robertsonian translocation. These assignments extend the conserved syntenic region between human chromosome 12 and mouse chromosome 10 that includes the genes for phenylalanine hydroxylase, gamma interferon, peptidase, and citrate synthase. The localization of histidase to mouse chromosome 10 suggests that the histidase regulatory locus (Hsd) and the histidinemia mutation (his), which are both known to be on chromosome 10, may be alleles of the histidase structural gene locus.

Amino Acid Metabolism, Inborn Errors↗
PubMed1991

Immunolocalization of the calpains and calpastatin in human and bovine platelets.

The structure of human platelets differs from that of bovine platelets in that human platelets have a surface-connected canalicular system that bovine platelets lack. Platelets are one of the richest known sources of the calpains, and the calpains have been implicated in many of the specific cleavages of cytoskeletal and surface-receptor proteins that occur during platelet activation and aggregation. Several studies have reported that human platelets are rich in mu-calpain and contain less m-calpain, whereas bovine platelets contain principally m-calpain and almost no mu-calpain. The immunolocalization studies reported here show that calpastatin is distributed throughout the cytosol of both human and bovine platelets and that calpain is located throughout the interior of human platelets. Calpain in bovine platelets is located primarily in alpha-granules, however. Because bovine platelets contain predominantly m-calpain and because alpha-granules are translocated to the platelet surface during activation, bovine m-calpain may be responsible for the specific cleavages of platelet surface proteins such as glycoprotein Ib that occur during platelet activation and at extracellular Ca2+ concentrations high enough to activate m-calpain.

Animals↗
PubMed1991

Histidase and histidinemia. Clinical and molecular considerations.

Histidase (histidine ammonia-lyase, EC 4.3.1.3) catalyzes the deamination of L-histidine to trans-urocanic acid in the liver and skin of mammals. Histidase deficiency results in increased histidine and histamine in blood, and decreased urocanic acid in blood and skin. In this review we discuss current research on: (1) the mechanism of formation of an unusual residue, dehydroalanine, at the active site of histidase; and (2) the role of urocanic acid as an ultraviolet light-induced immunoregulator in the skin, and the implications of urocanic acid deficiency for human histidinemia. Genetic mechanisms that may account for the 1% of histidinemic patients with neurological impairments are considered briefly.

Alanine↗
PubMed1990

Cloning and expression of rat histidase. Homology to two bacterial histidases and four phenylalanine ammonia-lyases.

Histidase (histidine ammonia-lyase, EC 4.3.1.3) catalyzes the deamination of histidine to urocanic acid. Apart from phenylalanine ammonia-lyase, which is not expressed in animals, histidase is the only enzyme known to have a dehydroalanine residue in its active site. The amino site precursor and the mechanism of formation of dehydroalanine are not known. As an initial step to determining the precursor of dehydroalanine in histidase, we have isolated a functional cDNA clone for histidase from a rat liver cDNA library using an affinity-purified antiserum. The 2.2-kilobase cDNA has a 1,971-base pair open reading frame coding for a 657-amino acid polypeptide with a predicted molecular mass of 72,165 Da. The cDNA has a rare polyadenylation signal (AAUACA) that appears to inefficiently direct polyadenylation in transfected COS monkey kidney cells. Conversion of this sequence to the consensus polyadenylation signal (AAUAAA) resulted in increased levels of stable mRNA. COS cells transfected with a histidase expression vector produce active histidase. The formation of active histidase in cells that have no endogenous histidase activity suggests either that the requisite modifying enzyme is present in these cells or that the dehydroalanine residue forms by an autocatalytic mechanism. Rat histidase was found to have 41 and 43% amino acid identity to Pseudomonas putida and Bacillus subtilis histidases, respectively. Phenylalanine ammonia-lyases from parsley, kidney bean, and two yeast strains were also found to have approximately 20% amino acid identity to rat histidase. On the basis of the similarity of function of histidase and phenylalanine ammonia-lyase, dehydroalanine at the active sites, and the sequence conservation over a large evolutionary distance (mammals, bacteria, yeast, and plants), we propose that the genes for histidase and phenylalanine ammonia-lyase have diverged from a common ancestral gene, of which the most conserved regions are likely to be involved in catalysis or dehydroalanine formation.

Amino Acid Sequence↗
PubMed1990

Glycoprotein Ib, von Willebrand factor, and glycoprotein IIb:IIIa are all involved in platelet adhesion to fibrin in flowing whole blood.

We have investigated the molecular basis of thrombus formation by measuring the extent of platelet deposition from flowing whole blood onto fibrin-coated glass coverslips under well-defined shear conditions in a rectangular perfusion chamber. Platelets readily and specifically adhered to fibrin-coated coverslips in 5 minute perfusion experiments done at either low (300 s-1) or high (1,300 s-1) wall shear rates. Scanning electron microscopic examination of fibrin-coated coverslips after perfusions showed surface coverage by a monolayer of adherent, partly spread platelets. Platelet adhesion to fibrin was effectively inhibited by a monoclonal antibody (MoAb) specific for glycoprotein (GP) IIb:IIIa. The dose-response curve for inhibition of adhesion by anti-GPIIb:IIIa at both shear rates paralleled that for inhibition of platelet aggregation. Platelet aggregation and adhesion to fibrin were also blocked by low concentrations of prostacyclin. In contrast, anti-GPIb reduced adhesion by 40% at 300 s-1 and by 70% at 1,300 s-1. A similar pattern of shear rate-dependent, incomplete inhibition resulted with a MoAb specific for the GPIb-recognition region of von Willebrand factor (vWF). Platelets from an individual with severe von Willebrand's disease, whose plasma and platelets contained essentially no vWF, exhibited defective adhesion to fibrin, especially at the higher shear rate. Addition of purified vWF restored adhesion to normal values. These results are consistent with a two-site model for platelet adhesion to fibrin, in which the GPIIb:IIIa complex is the primary receptor, with GPIb:vWF providing a secondary adhesion pathway that is especially important at high wall shear rates.

Antibodies, Monoclonal↗
PubMed1990

Ileal glucagon gene expression: ontogeny and response to massive small bowel resection.

Massive small bowel resection with re-anastomosis of the residual jejunum and terminal ileum results in marked adaptive responses. Various luminal and humoral factors have been implicated in the adaptive response, which may be analogous to the changes occurring in the ileum in the postnatal growth phase. Enteroglucagon, which is synthesized in the L cells of the intestinal mucosa, is thought to be an important humoral factor in this response. In this study, the levels of glucagon gene expression in the rat ileum both after massive small bowel resection and during development are examined. Glucagon messenger RNA levels are increased threefold as part of the adaptive response; the increase is maximal at 2 days and is at least partly dependent on luminal nutrition. Levels of glucagon messenger RNA in the developing ileum increase in the postnatal period until weaning when they decrease somewhat before gradually reaching adult levels.

Adaptation, Physiological↗
PubMed1990

Oxygen derived free radicals in osteoclasts: the specificity and location of the nitroblue tetrazolium reaction.

Oxygen derived free radicals are generated by osteoclasts. In a novel culture system, isolated rat osteoclasts were stained when nitroblue tetrazolium (NBT) was reduced by cellular oxidants to formazan, an insoluble precipitate. Superoxide dismutase (SOD) inhibited the accumulation of formazan by the isolated osteoclasts. Osteoclasts in mouse calvarial organ cultures also reduced NBT to formazan. The reaction products were localized to the area of the osteoclast-bone interface. At the light microscopic level, the formazan granules appeared to be concentrated within the cytoplasm. Formazan accumulation was significantly inhibited by calcitonin (hCT). The inhibition of NBT reduction by SOD indicates that the isolated osteoclasts were capable of producing superoxide. The localization of the formazan granules between the external osteoclastic membrane and the bone, and the inhibition of this reaction during hCT exposure suggests that oxygen derived free radicals may contribute to bone resorption.

Animals↗
PubMed1990

Enema or Picolax as preparation for flexible sigmoidoscopy?

Two preparations for outpatient flexible sigmoidoscopy, Picolax and Klyx enemas, have been compared in a randomized controlled trial. There was no difference in efficacy between the two preparations, but patients preferred Picolax.

Adolescent↗
PubMed1989

Effect of hind-limb suspension on young and adult skeletal muscle. I. Normal mice.

The purpose of this study was to determine the effect of hind-limb suspension (HS) on morphometric, histologic, and contractile characteristics of fast extensor digitorum longus (EDL) and slow soleus (SOL) twitch muscles in adult and immature mice. Hind-limb suspension for 2 weeks was used to produce atrophy in two groups of mice, ages 4 and 12 weeks, with nonsuspended animals serving as controls. Young HS mice exhibited marked decreases in SOL weight, length, cross-sectional area (CSA), twitch and tetanic tensions, and rates of tension development and relaxation, with increases in fatigue resistance. HS reduced the diameter of both type I and IIA fibers, increased the percentage of type I fibers, and decreased the percentage of type IIA fibers in both young and adult SOL. Muscle weight, length, CSA, IIA and IIB fiber areas, and maximum rate of tetanic tension development were decreased in EDL of young HS mice; fatigue resistance and EDL half-relaxation times were increased. For most parameters evaluated, slow twitch muscle was more affected than fast twitch. HS affected contractile characteristics less than morphometric or histologic parameters. Rates of tension development and relaxation were the contractile parameters most affected by HS, and the time parameters of contraction were least affected. For all measurements young mice were more affected than adult mice.

Aging↗