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Biomedical subjects

J M Davis

Publications and source records attributed to J M Davis.

At least 415 records · Page 23Linked to original sources
PubMed1988

Carbohydrate-electrolyte drinks: effects on endurance cycling in the heat.

On three occasions cyclists completed, as fast as possible, two exercise tasks (T1 and T2) separated by 30 min rest. T1 and T2 were equivalent to the work performed during 2 h cycling at 75% VO2max and 30 min at 75% VO2max, respectively. Every 20 min subjects drank 275 mL of a 6% (MC) or 2.5% (LC) carbohydrate-electrolyte beverage or a water placebo (P). The initial drink during both T1 and the rest period contained 20 g D2O as a marker for entry of ingested fluid into blood. No differences in drink effects were found for heart rate, sweat rate, change in plasma volume, rectal temperature, or D2O accumulation in blood. Blood glucose and respiratory exchange ratios were higher and T2 was performed faster with MC than with P. Ingestion of MC can help maintain blood glucose and enhance performance of prolonged cycling exercise without compromising fluid replenishment.

Adolescent↗
PubMed1988

Status of school children's hearing aids relative to monitoring practices.

Data concerning hearing aid monitoring practices and hearing aid malfunction were collected for three groups of mainstreamed hearing-impaired children: 248 children receiving services from itinerant teachers of the hearing impaired, 43 who participated in a study involving extensive psychoeducational evaluation, and 10 children who attended a 6 week residential treatment program in which hearing aid function was checked at least twice each day. Comparisons of the three data sets revealed that even conscientious parental and professional monitoring practices prove inadequate. As a result, it is hypothesized that children must take active roles in the monitoring process. A program to help children develop hearing aid monitoring skills is outlined.

Child↗
PubMed1988

Biosynthesis of Sucrose and Mannitol as a Function of Leaf Age in Celery (Apium graveolens L.).

In celery (Apium graveolens L.), the two major translocated carbohydrates are sucrose and the acyclic polyol mannitol. Their metabolism, however, is different and their specific functions are uncertain. To compare their roles in carbon partitioning and sink-source transitions, developmental changes in (14)CO(2) labeling, pool sizes, and key enzyme activities in leaf tissues were examined. The proportion of label in mannitol increased dramatically with leaf maturation whereas that in sucrose remained fairly constant. Mannitol content, however, was high in all leaves and sucrose content increased as leaves developed. Activities of mannose-6-P reductase, cytoplasmic and chloroplastic fructose-1,6-bisphosphatases, sucrose phosphate synthase, and sucrose synthase increased with leaf maturation and decreased as leaves senesced. Ribulose bisphosphate carboxylase and nonreversible glyceraldehyde-3-P dehydrogenase activities rose as leaves developed but did not decrease. Thus, sucrose is produced in all photosynthetically active leaves whereas mannitol is synthesized primarily in mature leaves and stored in all leaves. Onset of sucrose export in celery may result from sucrose accumulation in expanding leaves, but mannitol export is clearly unrelated to mannitol concentration. Mannitol export, however, appears to coincide with increased mannitol biosynthesis. Although mannitol and sucrose arise from a common precursor in celery, subsequent metabolism and transport must be regulated separately.

Journal Article↗
PubMed1988

Increased tubuloglomerular feed-back mediated suppression of glomerular filtration during acute volume expansion in rats.

1. Volume expansion is currently believed to change the intrinsic properties of the juxtaglomerular apparatus such that the sensitivity of the tubuloglomerular feedback (TGF) mechanism is reduced, thus allowing glomerular filtration rate, and hence salt and water excretion, to rise. Recent studies conflict with this view and indeed the older literature reveals that the rise in glomerular filtration rate (GFR) under these conditions is far more modest than would be expected if TGF control were eliminated. 2. To investigate this problem, TGF control of filtration rate was examined by measuring single-nephron glomerular filtration rate (SNGFR) during loop of Henle perfusion at varying rates in rats under control conditions, after acute, moderate (4% of body weight), iso-oncotic volume expansion and in rats treated with antibodies to atrial natriuretic peptide (ANP) prior to the acute volume expansion. 3. With TGF control of filtration interrupted by filtrate collection from the proximal tubule, SNGFR in the expanded rats was massively increased compared with controls, although SNGFR measured in the distal tubule, and hence with TGF control intact, was only modestly increased, as was whole-kidney filtration rate. Loop perfusion at increasing rates up to 30 nl min-1 progressively decreased SNGFR in controls, and in the expanded rats the range over which control was exerted extended up to 60-80 nl min-1. For changes in loop flow around the spontaneous operating point, the sensitivity of the TGF mechanism, defined as delta SNGFR/delta loop flow, was similar in both groups. Treatment of rats with ANP antibodies prior to volume expansion substantially blunted the changes in renal salt and water excretion and the increase in SNGFR seen in the absence of loop perfusion. 4. These results are not consistent with a diminution of TGF function after volume expansion, rather with an enhancement. The latter is best accounted for by vasodilation of preglomerular resistance vessels on volume expansion, a result predicted by calculations from a model based on the serial arrangement of preglomerular and TGF-controlled vascular resistance elements and the established pharmacological actions of ANP.

Animals↗
PubMed1988

The control of glomerular filtration rate and renal blood flow in chronically volume-expanded rats.

1. Chronic volume expansion by dietary salt loading practically abolishes tubuloglomerular feed-back (TGF) by means of a humoral inhibitor in tubular fluid. Elimination of the vasoconstrictor influence of feed-back does not, however, increase glomerular filtration rate (GFR) and renal blood flow (RBF), implying that chronic salt loading induces additional preglomerular vasoconstriction. This being so, the feed-back response which, although absent in free-flowing nephrons, can still be elicited by loop of Henle perfusion with Ringer solution, should be essentially normal, except that nephron GFR at any loop perfusion rate should be lower than in controls. Persistence of RBF, GFR and nephron GFR autoregulation would imply that autoregulation is achieved by a preglomerular resistance control system independent of feed-back. 2. These hypotheses were tested by clearance and micropuncture experiments in rats chronically fed a diet containing 40 g NaCl (kg food)-1. 3. RBF and GFR autoregulation indeed persisted, the former down to 90 mmHg compared with 105 mmHg in controls. In controls, nephron GFR measured distally was autoregulated down to 90 mmHg whereas that measured proximally was autoregulated only above 105 mmHg. In high-salt rats nephron GFR from both sites was autoregulated to 90 mmHg. 4. Loop of Henle perfusion with homologous tubular fluid in high-salt rats confirmed attenuation of feed-back. Loop perfusion with Ringer solution yielded a response comparable to that in controls (maximal reduction of nephron GFR to 57%, compared with 56% in controls). Absolute nephron GFR at any loop perfusion rate was lower in high-salt rats than in controls. 5. These observations confirm the initial hypotheses. Considering feed-back and autoregulation as independent, preglomerular resistance control mechanisms, together with elementary haemodynamic considerations, allows formulation of a renal haemodynamics model whose quantitative predictions regarding characteristics of RBF, GFR and feed-back control are remarkably consistent with the literature.

Animals↗
PubMed1988

Effects of electrostatic charge on the pathogenicity of chrysotile asbestos.

Two groups of 48 rats of the AF/HAN strain were exposed for one year to respirable dust clouds of UICC chrysotile asbestos at a dose level of 10 mg/m3. One group was treated with dust carrying the normal electrostatic charge produced during dust generation, whereas the other was exposed to dust discharged by exposure to ionising radiation from a thallium-204 source. After dusting most animals were retained for their full life span. At the end of the dusting period those animals treated with normally charged dust had significantly more chrysotile retained in their lungs than animals exposed to discharged dust. Subsequently, animals treated with normally charged dust developed more pulmonary fibrosis and more pulmonary tumours. These findings suggest that the charge carried by airborne fibres should be taken into account when considering the health risks from exposure to chrysotile. Highly charged fibres are more likely to be deposited in lung tissue and thus constitute a greater hazard.

Animals↗
PubMed1988

Cellular polypeptides overexpressed after herpes simplex infection permit virus subtyping and may help diagnose cervical cancer.

The synthesis of cellular macromolecules is inhibited after infection with herpes simplex viruses (HSV) although certain host proteins accumulate to high concentrations as identified by monoclonal antibody TG7A. By western blotting, a polypeptide with a relative molecular weight of 90 kilodaltons was identified in cells infected with type 2 viruses and a polypeptide of 40 kilodaltons relative molecular weight in type 1 infected cells, and virus typing was confirmed by restriction enzyme analysis of viral DNA. Thirty seven clinical isolates from the genital region were subtyped as HSV type 2 and 18 from the orofacial region as type 1 by the different intracellular location of the 90 kilodalton and 40 kilodalton proteins seen on immunofluorescent staining of cells infected with HSV. Expression of these proteins has been associated with cellular transformation due to gene products of HSV or other viruses. Overexpression of the cellular proteins identified by TG7A reactivity was shown to be a marker for cells in cervical smears from patients with CIN III that appeared to be dyskaryotic. Little or no reaction was observed in squamous epithelial cells found in normal or abnormal smears.

Antibodies, Monoclonal↗
PubMed1988

Kinetics of the bronchoalveolar leucocyte response in rats during exposure to equal airborne mass concentrations of quartz, chrysotile asbestos, or titanium dioxide.

The kinetics of the bronchoalveolar response was assessed in rats exposed, at equal airborne mass concentration (10 mg/m3), to titanium dioxide--a non-pathogenic dust--and the two pathogenic mineral dusts quartz and chrysotile asbestos. Rats were killed at intervals over a 75 day exposure period and groups of rats exposed for 32 and 75 days after recovery for two months. Bronchoalveolar lavage was carried out and the lavage fluid characterised for cellular content, macrophage activation, and concentrations of free total protein, lactate dehydrogenase, and N-acetyl-beta-D-glucosaminidase. Inhalation exposure to the two pathogenic dusts resulted in an increased number of leucocytes, macrophage activation, and increased levels of free enzymes and total protein. The pattern and magnitude of the responses to quartz and chrysotile differed. Chrysotile caused less inflammation than quartz, and the main cellular response peaked around the middle of the period of dust exposure whereas the highest levels of enzymes occurred towards the end. The difference in timing suggests that macrophages were not available for lavage towards the end of the exposure, owing to their playing a part possibly in deposition of granulation tissue. Quartz caused a greater cellular and enzyme response than chrysotile, particularly towards the end of the dust exposure phase. There was a noticeable progression of inflammation in the quartz exposed groups left to recover for two months, but not in the chrysotile recovery groups.

Animals↗
PubMed1988

Response of psychotic and nonpsychotic depression to phenelzine.

The authors studied 52 depressed inpatients to examine treatment response to phenelzine, a monoamine oxidase (MAO) inhibitor. All patients were classified into one of three RDC categories (definitely psychotic, probably psychotic, and nonpsychotic). For the entire sample, the mean platelet MAO inhibition level achieved with phenelzine was greater than 80%. Response to treatment was determined by independent clinical assessment and by the change in rating scores from baseline; 68% of the nonpsychotic, 43% of the probably psychotic, and 21% of the definitely psychotic patients were classified as responders. This differential response rate is similar to that reported in the literature for tricyclic antidepressants.

Antidepressive Agents, Tricyclic↗
PubMed1988

Fibrinolysis by rat mesothelial cells in vitro: the effect of mineral dusts at non-toxic doses.

Rat mesothelial cell cultures were shown to have considerable plasminogen dependent and independent fibrinolytic activity in vitro using an 125I fibrin degradation assay. At non-toxic doses of the mineral dusts titanium dioxide, quartz and crocidolite asbestos, as assessed by 51Cr release, the fibrinolytic activity of mesothelial cells was inhibited. Quartz had the greatest inhibitory effect and crocidolite asbestos had the least. These results suggests that inhibition of mesothelial cell fibrinolysis does not, on its own, explain pleural fibrosis due to toxic mineral dusts.

Animals↗
PubMed1988

Comparisons of the pathogenicity of long and short fibres of chrysotile asbestos in rats.

Long-term inhalation and intraperitoneal injection studies were undertaken with laboratory rats treated with a specially prepared short-fibre sample of Canadian chrysotile asbestos. This was compared, at an equal mass dose, to dust generated from the same chrysotile batch so as to contain the highest possible number of long fibres. The long-fibre cloud contained roughly five times more fibres greater than 5 micron in length as seen by phase contrast optical microscopy (PCOM). For increasing lengths, the ratio between the dust clouds increased progressively, reaching over 80: 1 for fibres greater than 30 microns in length. Rats treated with long-fibre chrysotile developed six times more advanced interstitial fibrosis (asbestosis) than animals treated with short-fibre chrysotile and three times more pulmonary tumours. At the end of the 12-month dusting period, three times more short chrysotile than long had been retained in the rat lung tissues. During the following 6 months, however, the short-fibre chrysotile was removed from the lungs much more rapidly than the long. Following intraperitoneal injection at a mass dose of 25mg of dust, both long and short chrysotile produced mesotheliomas in more than 90% of rats. At a dose level of 2.5mg of dust, the short-fibre chrysotile produced mesotheliomas in only one-third as many rats as the long-fibre dust which still produced mesotheliomas in more than 90% of animals injected. At a dose level of 0.25mg of dust, the short-fibre chrysotile produced no mesotheliomas while the long-fibre chrysotile still produced these tumours in 66% of rats. In the two highest doses, where short-fibre chrysotile produced mesotheliomas, the mean tumour induction period was significantly longer than for tumours produced by long chrysotile.

Animals↗
PubMed1988

Legal aspects of tardive dyskinesia.

While the therapeutic value of neuroleptics in the treatment of schizophrenia and psychoses is universally recognized, the risk of tardive dyskinesia linked to the use of these drugs raises ethical and legal problems for the physician. The authors discuss the basic principles linked to these legal aspects of the question: inappropriate indication of neuroleptic treatment, inadequate treatment monitoring, error in diagnosis of tardive dyskinesia and misconduct with regard to informed consent. The various aspects are illustrated by specific cases.

Antipsychotic Agents↗
PubMed1988

A comparison of thiothixene with chlorpromazine in the treatment of mania.

High potency neuroleptics have been advocated for acute mania because their side effect profile may allow for a more rapid dose escalation and symptom resolution. Low potency neuroleptics have also been advocated because their sedative properties might better calm the acutely agitated manic patient. The authors tested these hypotheses using a double-blind design comparing thiothixene with chlorpromazine in 29 manic patients on a standard dose of lithium. They found that thiothixene and chlorpromazine produced identical rates and degree of improvement, that side effect profiles differed for each drug but did not affect overall clinical response, and that most patients had a good response on much lower than expected doses. The implications for less aggressive use of neuroleptics to treat mania are discussed.

Adult↗