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Biomedical subjects

W Davison

Publications and source records attributed to W Davison.

At least 37 records · Page 2Linked to original sources
PubMed1996

Effects of preload and afterload on the performance of the in situ perfused portal heart of the New Zealand hagfish Eptatretus cirrhatus

The portal heart of the New Zealand hagfish (Eptatretus cirrhatus) was perfused in situ. Stroke volume, cardiac output and power output increased in response to increased preload, in accordance with Starling's law of the heart. A positive chronotropic effect was found when the input pressure increased from 0.05 to 0.1 kPa. Increased afterload decreased stroke volume and cardiac output. Power output peaked at an output pressure of 0.22 kPa, after which it decreased. There was no change in heart rate in response to increased afterload. In unanaesthetized resting animals, the pressure in the supraintestinal vein, which supplies the portal heart, ranged from 0.025 to 0.07 kPa (mean 0.040±0.005 kPa). The beta-adrenoceptor antagonist sotalol did not affect the response to different input and output pressures. Sotalol produced a significant decrease in heart rate and abolished the pressure-sensitive increase in heart rate. Bolus injections of adrenaline produced a transient increase in portal heart rate. The negative chronotropic response to sotalol and the response to adrenaline indicate the presence of an endogenous beta-adrenergic tonus on the portal heart.

Journal Article↗
PubMed1995

Chromosome elimination in three Baltic, south Pacific and north-east Pacific hagfish species.

We have confirmed that chromosome elimination occurs in the cells of Myxine glutinosa, collected from the Baltic Sea off Sweden, Eptatretus cirrhatus from the south Pacific Ocean off the east coast of New Zealand, and E. stoutii from the north-east Pacific Ocean off Canada, similar to cells of four Japanese hagfish species. In M. Glutinosa, E. cirrhatus type A, E. cirrhatus type B and E. stoutii, the differences in chromosome number between spermatogonia (44, 72, 80 and 48) and somatic cells (28, 34, 34 and 34) were 16, 38, 46 and 14 respectively. The amount of DNA eliminated from presumptive somatic cells averaged 43.5%, 48.7%, 54.6% and 52.8% respectively. Euchromatic chromosomes and/or parts of chromosomes in addition to heterochromatic chromosomes were clearly eliminated in E. cirrhatus and E. stoutii. Adding our previous observations of four Japanese hagfish species, chromosome elimination occurs in all seven of the hagfish species. These results suggest that this phenomenon, chromosome elimination, generally occurs in the order Myxinida. In addition, B-chromosomes were observed in the germ cells of E. cirrhatus and E. stoutii, similar to the cells of E. okinoseanus, E. burgeri and Paramyxine atami (E. atami). This fact suggests that B-chromosomes might exist generally in the family Eptatretidae.

Animals↗
PubMed1994

EVIDENCE OF REGULATORY MECHANISMS FOR THE DISTRIBUTION OF BLOOD BETWEEN THE ARTERIAL AND THE VENOUS COMPARTMENTS IN THE HAGFISH GILL POUCH

Of the extant vertebrate animals, the hagfishes are generally considered to be the group which diverged first from the ancestral vertebrate lineage, although molecular sequence analysis has recently suggested that they form a monophyletic group with lampreys (Stock and Whitt, 1992). The circulatory system of hagfishes has features that have been described as 'primitive' (Burggren et al. 1985), but their gills are effective gas exchangers. The gills are contained within discrete muscular pouches, and the anatomy of the blood system and ventilatory ducts has an ideal countercurrent arrangement (Mallatt and Paulsen, 1986; Elger, 1987). Reite (1969) first reported effects of catecholamines and other drugs on the branchial vasculature of hagfish. Recent studies of both perfused gills in situ and of blood flow in vivo have suggested that blood flow through the gills of hagfish is under tonic control by catecholamines (Axelsson et al. 1990; Forster et al. 1992). In teleosts, several studies have shown that adrenergic control mechanisms are involved in the distribution of blood between the arterio-arterial and the arterio-venous pathways of the gill vasculature (see Nilsson, 1983). Anatomical and ultrastructural studies have demonstrated the existence of similar pathways in hagfish (Cole, 1925; Mallatt and Paulsen, 1986; Elger, 1987). The experiments reported here demonstrate that, in the hagfish gill pouch, both adrenaline and isoprenaline can increase the proportion of fluid leaving via the efferent arterial route, at the expense of the venous outflow. Hagfish (Eptatretus cirrhatus Forster) were collected off Motunau, North Canterbury, New Zealand, and held in seawater aquaria until used. The masses of the 11 animals used in these experiments ranged from 680 to 1720 g with a mean of 1140±110 g (s.e.m.). Animals were anaesthetized in a 0.4 % solution of benzocaine in sea water. The hagfish were opened ventrally to expose the gills and their blood supply. Individual gill pouches were prepared for perfusion studies.

Journal Article↗
PubMed1992

Cardiovascular responses to hypoxia in the hagfish, Eptatretus cirrhatus.

Simultaneous measurements of cardiac output (Q), blood pressures and blood gases were made in the hagfish, Eptatretus cirrhatus, during exposure to hypoxia. The partial pressure of oxygen in the medium (PIO2) was reduced from 20.7 kPa to 8.0 kPa and then lowered to 5.3 kPa. At a PIO2 of 5.3 kPa there was a 40% increase in Q. Part of the increase may have been due to the increased activity of the animal at low PIO2. In recovery, when the animals were inactive, Q continued to rise to 160% of the control values. At 5.3 kPa, oxygen consumption (as determined by the Fick principle) fell to 29% of the normoxic value and was associated with increased branchial vascular resistance (Rg) and an increased diffusion limitation of the gills (Ldiff). Adrenaline increased heart rate and aortic blood pressures. Increased Rg and Ldiff could be provoked in normoxia by the injection of the beta-adrenergic blocking drug propranolol. We suggest that catecholamines may be involved in the tonic control of gill vasomotor tone.

Animals↗
PubMed1992

Cardiovascular responses of the red-blooded antarctic fishes Pagothenia bernacchii and P. borchgrevinki.

The aim of this study was to investigate cardiac performance and cardiovascular control in two red-blooded nototheniid species of antarctic fishes, Pagothenia bernacchii (a benthic fish) and P. borchgrevinki (a cryopelagic fish), and to make comparisons with existing information on haemoglobin-free antarctic teleosts. In quiescent P. bernacchii at 0 degrees C ventral aortic pressure (PVA) was 3.09 kPa and cardiac output (Q) was 17.6 ml min-1 kg-1, with a heart rate (fH) of 10.5 beats min-1 and stroke volume of 1.56 ml kg-1. Following atropine treatment, Q was maintained but heart rate increased and stroke volume decreased. Resting heart rate resulted from an inhibitory cholinergic tone of 80.4% and an excitatory adrenergic tone of 27.5%. The intrinsic heart rate was 21.7 beats min-1 at 0 degrees C. In quiescent P. borchgrevinki at 0 degrees C, PVA was 3.6 kPa, Q was 29.6 ml min-1 kg-1 and stroke volume was 2.16 ml kg-1. The resting heart rate in P. borchgrevinki of 11.3 beats min-1 resulted from an inhibitory cholinergic tone of 54.5% and an excitatory adrenergic tone of 3.2%. The intrinsic heart rate was 23.3 beats min-1. P. bernacchii maintained Q during a progressive decrease in water oxygen tension from 20 to 6.7 kPa, but fH was increased significantly. Thus, although there is cholinergic control of the heart, no hypoxic bradycardia was observed. Recovery from hypoxia was associated with increases in Q and fH; stroke volume returned to control values. PVA declined in recovery as total vascular resistance decreased. Hypoxic exposure following atropine treatment resulted in progressive increases in PVA, Q and stroke volume; fH decreased during the recovery period. Hypoxic exposure in P. borchgrevinki produced similar cardiovascular responses to those observed in P. bernacchii. During an acute increase in water temperature from 0 to 5 degrees C, P. bernacchii regulated Q and total vascular resistance. Stroke volume decreased as fH increased. The intrinsic heart rate had a Q10 of 1.96 over this temperature range. P. bernacchii maintained chronotropic inhibition up to a temperature of 2.5-3.0 degrees C. However, by 5 degrees C this chronotropic inhibition of the heart rate was lost. Infusion of adrenaline into the ventral aorta of P. bernacchii resulted in significant increases in Q, fH, PVA and total vascular resistance. Infusion of adrenaline after atropine treatment caused similar cardiovascular changes without the change in fH. P. borchgrevinki could sustain swimming in a water tunnel at approximately 1 body length per second for 6-10 min.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗
PubMed1989

Reclamation of acid waters using sewage sludge.

An exhausted sand quarry which had filled with acid water (pH 3) from the oxidation of pyrite was treated with calcium hydroxide to neutralize the water (pH 8), and sewage sludge to prevent further ingress of acid. The water remained neutral for 2 years, an appreciable quantity of base being generated by the reduction of sulphate to sulphide in the anoxic sediment formed by the sewage sludge. After this time the water reverted to acid conditions, chiefly because the lake was too shallow to retain the sewage sludge over a sufficiently large area of its bed. Incubation experiments showed that the sewage sludge had a large capacity for sulphate reduction, which was equally efficient in acid or neutral waters and that the areal rate of consumption was sufficiently fast to neutralize all incoming acid, if at least 50% of the lake bed was covered with sludge. Throughout the course of the field investigations there was no foul smell and the lake was quickly colonized by phytoplankton, macrophytes and insects. Although nutrients associated with the sewage sludge stimulated photosynthesis and so caused the generation of additional organic matter, they were exhausted within two years. To ensure permanent reclamation, phosphate fertilizer could be added once the initial supply has been consumed. Neutralization removed trace metals from the system, presumably due to formation of insoluble oxyhydroxide and carbonates. The solubility of aluminium was apparently controlled by a basic aluminium sulphate (jurbanite).

Journal Article↗
PubMed1987

Arterioles in the swimming muscles of the leatherjacket Parika scaber (Pisces: Balistidae).

The leatherjacket (Parika scaber) is a balistiform fish which swims using its dorsal and anal median fins. The muscles controlling these fins are well vascularised, with control of blood flow effected by arterioles. These arterioles are long with a single layer of smooth muscle surrounding the endothelium, although the amount of contractile material is sparse, probably a consequence of the low blood pressure. The endothelial cells contain microfilaments, probably contractile, running along the length of the arteriole. The function of this material is unknown.

Animals↗
PubMed1986

Blood oxygen transport in the free-swimming hagfish, Eptatretus cirrhatus.

Arterial and mixed venous blood were sampled through chronically implanted cannulae from rested and swimming hagfish. PaO2 remained high when hagfish were swum for 15 min at a velocity of 20 cm s-1. PvO2 fell from 17.2 mmHg at rest to 3.5 mmHg after swimming, and the arteriovenous pH difference increased from 0.15 to 0.25 pH units. Whole blood oxygen equilibrium curves were essentially hyperbolic (Hill's n value = 1.38) and gave a half-saturation PO2 (P50) value of 12.3 mmHg at pH 7.8 and 16 degrees C. A CO2-Bohr factor (phi = delta logP50/delta pH) of -0.43 and a limited buffering capacity of the blood, amounting to approx. 4 slykes, were observed. The role of the blood in transporting oxygen and carbon dioxide both at rest and after swimming is established by in vivo blood gas measurements and in vitro oxygen-binding data. The low internal PvO2 at rest is close to the P50 measured under similar conditions and the hyperbolic equilibrium curve permits further oxygen unloading when PvO2 falls during swimming.

Acid-Base Equilibrium↗
PubMed1983

Metabolic adjustments to diving and recovery in the African lungfish.

The metabolic potentials of the heart, brain, white muscle, and liver in the African lungfish were estimated by enzymatic data. Metabolic effects of a 12-h submergence were monitored using metabolite measurements. Heart was the most oxidative tissue but also showed the greatest anaerobic potential. The brain displayed relatively low oxidative capabilities. White muscle remained almost inert. Although high-energy phosphate concentrations in brain and heart did not fall during submergence, glycolysis was activated as indicated by crossover plots, depletion of endogenous glycogen stores, and lactate accumulation. Blood-tissue lactate and glucose gradients indicated 1) that the heart and brain released lactate throughout submergence, 2) that after 12 h of submersion the brain and heart were probably obtaining all their required glucose from the blood, 3) that the liver released glucose throughout submergence, and 4) that white muscle was metabolically isolated from the rest of the body during submergence. It appeared that perfusion adjustments occurring during submergence were directed more toward regulating intertissue exchange of metabolites than toward oxygen conservation. Comparisons are made to diving responses in mammals.

Anaerobiosis↗
PubMed1983

Evidence for a dose-dependent inflammatory response to quartz in the rat lung and its significance in early changes in collagen metabolism.

The response of the rat lung to a range of doses of quartz at 50 and 100 days after its administration by intratracheal instillation has been assessed by bronchopulmonary lavage. The effects on the number of polymorphonuclear leukocytes (PMN), lymphocytes and macrophages are described. In addition the concentrations of soluble protein and hydroxyproline and the activities of lactate dehydrogenase, PZ peptidase and collagenase in lavage fluid supernatants were measured and an assessment of the hydroxyproline content of recovered cells was made. Finally PZ peptidase and collagenase were assayed in PMN-enriched cell fractions and in samples obtained from short-term culture of recovered macrophages. There was a dose-dependent increase in the recovery of all three cell types, and in the amounts of lactate dehydrogenase, protein and hydroxyproline in lavage fluids, which showed no signs of resolution over the 100-day period studied. Measurements of PZ peptidase and collagenase suggested that the PMN, not the macrophages, are the major source of these degradative enzymes. The relevance of these findings with regard to the importance of PMN in quartz-induced fibrosis is discussed.

Animals↗
PubMed1983

The advantages and limitations of an in vivo test system for investigating the cytotoxicity and fibrogenicity of fibrous dusts.

The acute response of the rat lung to a range of fibrous materials has been investigated by bronchopulmonary lavage, at dose levels of 0.5 and 1.0 mg, 1 and 7 days after their administration by intratracheal instillation. The materials chosen for study included UICC chrysotile A, amosite, crocidolite and anthophyllite, and samples of S. African "long" amosite and glass fiber. In addition, the subacute response to 1, 2 and 3 mg of chrysotile and amosite has been studied at 50 and 100 days after instillation. In the acute phase at 1 day after instillation, the response to chrysotile was greater than that to any of the other materials, but by 7 days there was no gradation in the response to different dusts. In the subacute phase, cell recoveries were low, and it was not possible to assess the long-term cytotoxic or fibrogenic effects of amosite and chrysotile by analyses of lung washes, even though biochemical and histological methods indicated gross changes in lung pathology.

Animals↗
PubMed1983

Dose-dependent effects in the subacute response of the rat lung to quartz. I. The cellular response and the activity of lactate dehydrogenase in the airways.

The response of the rat lung to a range of doses of quartz at 50 and 100 days after its administration by intratracheal instillation was investigated by bronchopulmonary lavage. The effects on the numbers of polymorphonuclear leucocytes, lymphocytes and macrophages recovered are described. In addition, the size distribution of the recovered macrophages was followed and measurements of total numbers of macrophages in the lung were made using a radioactive tracer technique. Finally, the activity of the cytoplasmic enzyme, lactate dehydrogenase, in lavage fluid supernatants was recorded. There was a dose-dependent increase in the recovery of all three cell types and an increase in the total numbers of macrophages in the lungs which showed no signs of resolution over the 100 day period studied. Increasing levels of lactate dehydrogenase were also dose-dependent and well correlated with the numbers of polymorphs and lymphocytes recovered. The importance of this prolonged inflammatory reaction in relation to the fibrogenic action of quartz is discussed.

Animals↗
PubMed1982

The hare and the tortoise: metabolic strategies in cardiac and skeletal muscles of the skink and the chameleon.

Two lizards--a skink capable of fast short dashes, and a chameleon, incapable of fast movement--have been studied to determine the degree of metabolic diversity that exists in this group of reptiles. Oxygen uptake measurements, skeletal muscle histochemistry, and enzyme and metabolite levels in cardiac and skeletal muscles reveal that the skink has a higher metabolic potential, both aerobic and anaerobic, than the chameleon. The difference, however, is not as large as is indicated by the behaviors of the two lizards. Levels of citrate synthase and B-hydroxybutaryl CoA dehydrogenase in the hearts of both the lizards are high and indicate mammalian-level metabolic capabilities.

Animals↗
PubMed1982

Upper gastrointestinal barium studies in the elderly: follow-up in 101 patients.

A A retrospective study of 101 elderly patients who were referred for upper gastrointestinal barium studies showed that this led to a change of management in 36 patients. The commonest management change was endoscopic referral (10 patients). However, in only on patient did this sequence lead to surgery and this was merely palliative. Dysphagia, vomiting and weight loss were shown to be the presenting features most likely to result in an abnormal barium study. The most frequently detected abnormalities were hiatus hernia, reflux, oesophageal stricture, peptic ulcer and gastric carcinoma.

Aged↗
PubMed1981

An ultrastructural and histochemical study of the axial musculature in the African lungfish.

Red, intermediate, and white axial muscle fibres of African lungfish were studied using histochemical techniques and electron microscopy. Gross dissection revealed the presence of a small wedge of red coloured muscle along the lateral line. This wedge was shown by histochemical demonstrations of lactate and succinate dehydrogenases, of adenosine triphosphatases, and of lipid to be composed of a mosaic of red and intermediate fibres measuring 23.63 and 34.30 micrometer in average diameter, respectively. The bulk of the myotome was composed of white fibres having an average diameter of 67.35 micrometer. Mitochondrial density, capillarity and lipid content were very low for all fibres. These data suggest that the axial musculature is geared primarily for anaerobic function. The mosaic arrangement of fibres, and the lack of a subsarcolemmal band of mitochondria suggests that the lungfish have a muscle organisation that is transitional between lower vertebrates and amphibians.

Adenosine Triphosphatases↗