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Biomedical subjects

S Osborne

Publications and source records attributed to S Osborne.

At least 19 recordsLinked to original sources
PubMed1996

Alanine scan and N-methyl amide derivatives of Ac-bombesin[7-14]. Development of a proposed binding conformation at the neuromedin B (NMB) and gastrin releasing peptide (GRP) receptors.

Alanine and N-methylation scans together with molecular modelling were implemented in order to propose a binding conformation of the minimum active fragment of bombesin (BB), Ac-BB[7-14], to the gastrin releasing peptide (GRP) and neuromedin B (NMB) receptors. These data are also used to critically evaluate the previously proposed binding conformations such as alpha-helix and antiparallel beta-sheets. This shows that the previously reported conformations do not satisfy the experimental data. A new binding conformation of Ac-BB[7-14] is proposed consisting of three consecutive gamma-turns followed by a bend and finishing with two gamma-turns. This low energy conformation (analogous to a fragment of thymidylate synthase, 2TSC) of bombesin stabilized by five internal hydrogen bonds, and with the side chains of residues Trp8 and Leu13 held on the same side of the peptide, is in agreement with the experimentally observed data. This and the results of molecular modelling may aid in the synthesis of conformationally restricted high affinity bombesin analogues and/or high affinity template-based GRP or NMB receptor agonists and antagonists.

Amides↗
PubMed1995

Diaphragm and phrenic nerve activities during inspiratory loading in anesthetized rabbits.

To determine whether decreases in neural activation and/or neuromuscular transmission to the diaphragm contribute to ventilatory failure observed during inspiratory resistive loaded breathing, peak integrated activity of the intact phrenic nerve (ENGdi) and costal diaphragm (EMGdi), transdiaphragmatic pressure swings (Pdi) and evoked diaphragm compound action potentials (M-wave) were measured in anesthetized rabbits subjected to inspiratory resistive loads of varying intensities and duration breathing supplemental oxygen. Sustainable loads were studied for 4 h. Severe loads were applied in increments and studied for 50 min each. Loading resulted in parallel increases in ENGdi, EMGdi and Pdi that stabilized within 20 min. With severe loading, peak inspiratory pressure (Pao = -55 +/- 4 cm H2O) was maintained for 30 min after which there was a significant drop in inspiratory pressure (task failure). Despite hypoventilation and profound changes in blood gases, both activation (ENGdi) and neuromuscular transmission (ENGdi/EMGdi ratio or M-wave) were maintained throughout all loads even at task failure when a critical level of PaO2 (27 +/- 1 mm Hg) was reached. We conclude that neural activation and neuromuscular transmission to the diaphragm do not fail during inspiratory resistive breathing and discuss our findings in terms of current concepts of diaphragm fatigue and control of breathing in this model.

Anesthesia↗
PubMed1995

Epitope mapping of the NS4 and NS5 gene products of hepatitis C virus and the use of a chimeric NS4-NS5 synthetic peptide for serodiagnosis.

Specific domains of the NS4 and NS5 gene products of hepatitis C virus have been identified using hydrophilicity profiles for the prediction of potential immunogenic regions, and epitope scanning techniques. Peptides synthesised on the basis of such data show excellent reactivity in the ELISA format. Introduction of a glycine-glycine spacer between two peptides (NS4-12 and NS5-44) to give a single chimeric peptides does not appear to impair immunoreactivity. An ELISA based on the chimeric peptide and a Core-NS3 recombinant protein correctly diagnoses a cohort of haemodialysed patients, three commercial HCV panels and the sera of a negative control population.

Amino Acid Sequence↗
PubMed1995

A new model of neonatal stroke: reversible middle cerebral artery occlusion in the rat pup.

Neonatal stroke remains a complex pathophysiologic process that is poorly understood and difficult to investigate. The primary animal model used to study this phenomenon is that of unilateral carotid artery ligation with 2-3 hours exposure to severe hypoxia. A new model of neonatal stroke was developed based on transient middle cerebral artery occlusion without craniectomy. In this model a #6-0 (0.07 mm) nylon filament is passed via the carotid artery to occlude reversibly the middle cerebral artery for 4 hours under conditions of normoxia in 14- to 18-day-old spontaneously hypertensive rat pups. After removal of the filament and reperfusion for 24 hours, the infarct volume was determined using the mitochondrial stain, 2,3,5-triphenyltetrazolium chloride. Using this technique, a neocortical and caudoputamenal infarct affecting 49% of hemispheric volume that measured 180 +/- 29 mm3 (hemisphere volume = 359 +/- 16 mm3, mean +/- SEM) was created in 90% of animals (n = 8) undergoing this procedure. This model has the advantage of being relatively noninvasive, of not requiring global exposure of brain to hypoxia, and of using temporary rather than permanent occlusion. This technique should improve the ability to study the acute and long-term pathophysiology of neonatal stroke, particularly the phenomenon of reperfusion injury, as well as its sequelae in the developing nervous system.

Animals↗
PubMed1995

From 19th century nursing reforms to current practice: a selective overview with special reference to The Royal London Homoeopathic Hospital (The Royal London Homoeopathic Hospital NHS trust from 1993).

Early nursing reforms in the 19th century are usually associated with Nightingale, although later emphasis has been placed on similar movements in the Poor Law sector. Extension of nursing influence over decision-making in terms of nursing practice and education is charted, using examples from 19th century Minutes of hospital committees and more recent experience based mainly on the observations made by one of the writers, who had substantial input into steering the hospital through the stages prior to achieving National Health Service (NHS) Trust status. The significance of nurse executive power following the 1990s NHS reforms is highlighted and means of extending the use of this authority are explored.

Health Care Reform↗
PubMed1995

Stability of evoked parasternal intercostal muscle electromyogram at increased end-expiratory lung volume.

The diaphragmatic electromyogram has been measured as an index of the level of diaphragmatic activation. The diaphragmatic electromyogram, however, even when measured by intramuscular electrodes, can be artifactually altered by a change in lung volume (A. Brancatisano, S. M. Kelly, A. Tully, S. H. Loring, and L. A. Engel. J. Appl. Physiol. 66: 1699-1705, 1989) or by a change in body position. The parasternal intercostal muscle may be less subject to the mechanisms that are believed to produce this artifactual change. We asked whether the parasternal intercostal electromyographic activity could be reliable when lung volume changes. Six supine rabbits were anesthetized with ketamine and xylazine. Fine bipolar copper wires, with their tips exposed, were inserted into the left parasternal intercostal muscle in the third interspace. A stimulus that was three times maximal was applied to the corresponding intercostal nerve, and the resulting action potential (AP) was photographed. Parasternal intercostal muscle length was measured by sonomicrometry over the vital capacity range. There were small nonsignificant changes in the AP from functional residual capacity (FRC) to total lung capacity. From FRC to residual volume there was variation in the AP. The AP was also quite stable when regional conductivity was altered but showed variation when the parasternal intercostal muscle length change was accentuated by traction on the rib cage. We conclude that the parasternal intercostal electromyographic activity can be reliably used to measure inspiratory motoneuron output to it over the range of lung volumes from FRC to total lung capacity.

Animals↗
PubMed1995

Phrenic motoneuron firing rates during brief inspiratory resistive loads.

The neural activation of the diaphragm during quiet and vigorously stimulated breathing has been hypothesized to be submaximal. In this study, we measured phrenic motoneuron firing rates during brief progressively increasing inspiratory resistive loads in anesthetized rabbits. We recorded activity in 68 phrenic motoneurons in 17 rabbits. We found that 40 of these axons were active during quiet breathing. Twenty-seven axons were silent during quiet breathing but began to fire as inspiratory loading progressed. The level of drive reflected by transdiaphragmatic pressure where silent phrenic motoneurons were recruited ranged from 5 to 45 cmH2O. Silent motoneurons showed significantly higher average rates of firing and significantly greater increases in firing rate as loading progressed (P < 0.01). The firing rate of both active and silent axons tended to plateau as rates approached 70-80 Hz. All motoneurons except for one, which may have been an afferent, were activated by inspiratory resistive loading. Inspiratory resistive loading activated phrenic motoneurons at high rates, and our results did not support the presence of significant numbers of unrecruited motoneurons.

Animals↗
PubMed1995

L-NAME reduces infarct volume in a filament model of transient middle cerebral artery occlusion in the rat pup.

The importance of nitric oxide (NO) during focal cerebral ischemia remains controversial as studies have suggested both a neurotoxic and neuroprotective role. In the 7 d old rat pup, NG-nitro-L-arginine, a nitric oxide synthase inhibitor, reduced infarct volume in a model of unilateral carotid ligation with 2.5 h exposure to 8% O2. The current study examined whether NO is neurotoxic in a filament model of transient middle cerebral artery occlusion (MCAO) in the 14-18-d-old rat pup. We developed a reproducible filament model of transient MCAO in 14-18-d-old spontaneously hypertensive rats (35 g) by passing a no. 6-0 (0.07-mm) nylon filament via the carotid artery to occlude the middle cerebral artery for 4 h under normoxic conditions. After filament removal and reperfusion for 24 h, we determined infarct volume using the mitochondrial stain 2,3,5-triphenyltetrazolium chloride. NO synthesis was inhibited using NG-nitro-L-arginine methyl ester (L-NAME) at a dose of 3 mg/kg, intraperitoneally, 1 h before MCAO. We measured infarct volume in control (n = 7) and L-NAME (n = 7) groups. L-NAME reduced infarct volume by 55% (p < 0.01). In the control group, infarct volume (180 +/- 29 mm3) averaged 49 +/- 7% of the left hemisphere (359 +/- 16 mm3). In the L-NAME-treated group, infarct volume (77 +/- 19 mm3) was 22 +/- 5% of the left hemispheric volume (344 +/- 2 mm3). These findings support earlier studies that used models of neonatal hypoxic-ischemic brain injury and suggest a neurotoxic role of NO. They extend these observations by demonstrating a significant reduction in infarct volume in a stroke model in the immature rat pup.

Animals↗
PubMed1993

Probing the role of metal ions in the mechanism of inositol monophosphatase by site-directed mutagenesis.

Since inhibition of myo-inositol monophosphatase (EC 3.1.3.25) by lithium ions and the resulting attenuation of phosphatidylinositol cycle activity may be the mechanism by which lithium exerts its therapeutic effect in the treatment of manic depression, it is of great interest to understand the mechanism of the enzyme and how lithium and other metals interact with it. Divalent magnesium is essential for enzyme activity, whereas Li+ and high concentrations of Mg2+ act as uncompetitive inhibitors with respect to substrate. From the recently solved crystal structure of the human enzyme, several amino acid residues in the active site were targeted for mutagenesis studies. Nine single-residue substituted mutants were characterized with regard to catalytic parameters, Mg2+ dependence, and Li+ inhibition. In addition, a terbium fluorescence assay was developed to determine the metal binding properties of the wild-type and mutant enzymes. Although none of these mutations affected Km for substrate substantially, the mutations Glu70-->Gln, Glu70-->Asp, Asp90-->Asn and Thr95-->Ala, in which residues within coordinating distance of the active site metal were modified, all resulted in large reductions in catalytic activity. The position of Glu70 in the crystal structure further suggests that this residue may be involved in activating water for nucleophilic attack on the substrate. The mutations Lys36-->Ile, Asp90-->Asn, Thr95-->Ala, Thr95-->Ser, His217-->Gln, and Cys218-->Ala all resulted in parallel reductions in both lithium and magnesium affinity, suggesting that Li+ and Mg2+ share a common binding site.

Base Sequence↗
PubMed1993

Expression in E. coli and purification of a chimeric p22-NS3 recombinant antigen of hepatitis C virus (HCV).

A recombinant antigen (p22-NS3), possessing putative HCV nucleocapsid protein (p22) and non-structural protein 3 (NS3) epitopes, was heavily expressed in E. coli and purified. The p22-NS3 purified recombinant antigen strongly reacts with sera containing human antibodies directed against p22 and NS3 providing a starting point for the design of an HCV single all-encompassing antigen for a blood screening assay.

Antigens, Viral↗
PubMed1993

Purification of recombinant hepatitis delta antigen expressed in E. coli cells.

Recombinant DNA technology enables the massive production of recombinant hepatitis delta antigen (recHDAg) retaining immunological properties and transport functions. However, purification procedures of the recombinant delta antigen have, to date, not been described in the literature. We present a purification procedure allowing one to obtain highly purified recHDAg from bacterial cells expressing the hepatitis delta antigen.

Antigens, Viral↗
PubMed1993

Ventilation is coupled to metabolic demands during progressive hypothermia in rodents.

We examined changes in ventilation and metabolic rate during hypothermia (36-27 degrees C) induced with exposure to helium-oxygen and cold in halothane anesthetized ground squirrels (Spermophilus lateralis) and rats. As a consequence of proportionate decreases in VCO2 and breathing frequency, the VE/VCO2 in both species remained constant. The changes which occurred in breathing pattern were also similar in the two species; an increase in TI and TE along with emergence of apneic periods between breaths at body temperatures below 31 degrees C. VT/TI and TI/TTOT decreased but VT remained constant with progressive hypothermia. The ventilatory responses to hypercapnia and hypoxia decreased to the same extent as the ventilatory and metabolic requirements in the ground squirrel but not the rat. The changes in VE and VCO2 during hypothermia in the ground squirrel predicted well the values observed in deep hibernation. We conclude that regulation of ventilation at reduced body temperatures is tightly coupled to metabolic demand.

Animals↗
PubMed1993

Delayed poststimulus decrease of phrenic motoneuron output produced by phrenic nerve afferent stimulation.

The immediate effects of phrenic afferent nerve activation on ventilation have been shown to be both excitatory and inhibitory. Long-lasting inhibitory effects on respiratory motoneuron output have been reported after stimulation of afferent nerves from limb muscles. However, whether respiratory muscle afferent nerves can produce this effect is unknown. We therefore hypothesized that activation of phrenic afferent nerves may produce a prolonged decrease of respiratory motoneuron output. Six alpha-chloralose-anesthetized dogs were studied after vagotomy and bilateral carotid sinus nerve section. The dogs were paralyzed, and end-tidal CO2 was controlled by mechanical ventilation. The proximal end of the cut thoracic phrenic nerve was electrically stimulated for 1 min at intensities that produced activation of thin-fiber afferents. The contralateral efferent phrenic integrated electroneurogram (ENG) was recorded. During stimulation, phrenic ENG activity increased. ENG activity was recorded during recovery and reached a peak decrease compared with control of 19 +/- 11% (SD) 9.0 +/- 6 min after stimulation and returned to control after 30 min. A qualitatively similar response was seen after stimulation of the gastrocnemius nerve. We conclude that activation of thin-fiber afferents in the phrenic nerve can produce a delayed and prolonged decrease of respiratory motoneuron output similar to that of limb muscle afferent nerves.

Anesthesia↗
PubMed1992

Daily monitoring and correction of radiation field placement using a video-based portal imaging system: a pilot study.

We have developed a video-based portal imaging system for radiotherapy localization. The system can acquire high quality portal images automatically using short (1-3 monitor unit) irradiations and immediately display the images. The major advantage of the imaging system is that it can be used routinely to check and correct patient positioning before much of the daily irradiation has been delivered. The portal imaging system has been used in a pilot study to monitor five patients during each of their daily treatments. The study has shown that: (i) image quality is sufficiently high to detect discrepancies in field placement from that prescribed on the simulator film; (ii) discrepancies in field placement occur frequently; and, (iii) routine correction of patient and block positioning can reduce the size of these discrepancies. This is the first time that field placement in radiation therapy has been checked and corrected routinely, before the treatment irradiation. However, limitations in the size of the field of view and in the methods of extracting and presenting the geometric information to the users limits the clinical utility of the imaging system. Solutions to these limitations are currently under development.

Computer Terminals↗
PubMed1992

Effect of vagal stimulation and parenteral acetylcholine on canine trachealis muscle shortening.

Canine trachealis smooth muscle shortening (TMS) in response to vagal nerve stimulation is approximately 30%, far less than the 70% predicted from in vitro studies. We hypothesized that in vivo airway smooth muscle activation during vagal stimulation may be submaximal, and in this study we wished to determine TMS during maximal activation. TMS was studied in 12 alpha-chloralose-anesthetized dogs during vagal stimulation, systemic acetylcholine injection, and local acetylcholine injection. Bilateral vagal stimulation produced TMS of 26 +/- 5% (SE) length at functional residual capacity (LFRC). Maximal TMS during systemic injection of acetylcholine was 28 +/- 12% LFRC but may have been limited by delivery of acetylcholine to the muscle because asystole occurred at higher concentrations. TMS was greatest during local injection of acetylcholine (48 +/- 7% LFRC). There was a greater increase in pulmonary resistance and decrease in dynamic compliance during systemic acetylcholine injection than during vagal stimulation. We conclude that bilateral vagal nerve stimulation does not maximally activate trachealis smooth muscle but that the maximal shortening achieved with local injection of acetylcholine is still less than isotonic shortening in vitro. These data suggest that maximal shortening in vivo is limited by the afterload provided by the tracheal cartilaginous rings.

Acetylcholine↗
PubMed1992

Monocyte inflammatory mediators impair in vitro hamster diaphragm contractility.

Sepsis has been shown to impair ventilatory muscle function. To determine whether this can be attributed to direct effects of inflammatory mediators on muscle fibers, we carried out in vitro studies on hamster costal diaphragm. Baseline measurements included supramaximal peak twitch (Pt) and tetanic tension (Po), twitch half relaxation time (1/2RT) and time-to-peak tension (TTP), and force frequency response (15 to 80 Hz). Fatigability was evaluated using 60-Hz stimulations at a duty cycle of 0.4 until tension fell to 50% of baseline. Preparations were then incubated in one of the following for 60 min: (1) Krebs solution (n = 5), (2) nonstimulated monocyte supernatant (n = 5), or (3) lipopolysaccharide-stimulated monocyte supernatant (n = 5). Baseline Pt, Po, 1/2RT, TTP, force frequency response, and fatigue profile were similar between groups. After incubation there was a significant fall in Pt (mean +/- SD, 538 +/- 65 to 288 +/- 13 g/cm2, p < 0.05) and Po (1,268 +/- 132 to 921 +/- 64 g/cm2, p < 0.05) in the LPS group, with no change in the other groups. There was no change in TTP; however, 1/2RT was lower in the LPS-stimulated group after incubation (p < 0.05). There was a rightward shift in the force frequency response for the LPS-stimulated group (p < 0.05). When normalizing for initial Po, there was no significant change in the time to fatigue for any of the three groups. This study demonstrated that monocyte secretory products impair diaphragmatic contractility in vitro by a direct effect on muscle fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Exponential analysis of the pressure-volume curve. Correlation with mean linear intercept and emphysema in human lungs.

We investigated the effect of obvious emphysematous lesions and the mean airspace size in the lung surrounding these lesions on the exponential constant K of the lung pressure-volume curve. The severity of the centrilobular emphysematous (CLE) lesions was determined in resected lung specimens, and the mean linear intercept (Lm) was measured on random histologic sections taken from regions without obvious emphysema. The exponential constant K was determined by fitting lung pressure-volume data obtained from the patient just prior to resection to the equation V = A - Be-KP. This allowed us to compare patients with little or no emphysema that had either normal (0.16 +/- 0.03 SD; n = 12) or increased (0.27 +/- 0.04 SD; n = 12) K to other patients that had severe emphysema but either normal (0.17 +/- 0.01 SD; n = 10) or increased (0.25 +/- 0.03 SD; n = 10) K. In subjects without emphysema, K was significantly related to Lm, suggesting that K is a measure of mean alveolar size. In the subjects with emphysema, a lower value for K was associated with more severe airway dysfunction and gas trapping. We conclude that K reflects airspace size except when airway closure subtracts the contribution of lung units from the deflation pressure-volume curve.

Aged↗