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Biomedical subjects

P Canfield

Publications and source records attributed to P Canfield.

32 records · Page 2Linked to original sources
PubMed1989

Effect of luminal perfusion rate on duodenal alkalinization in the rat in vivo and in vitro.

This study investigates the effects of luminal perfusion rate on the observed rate of alkalinization of an unbuffered saline by anesthetized rat distal duodenum. Increases in perfusion rate (range 0.3-22 ml/min) increased both alkalinization (3-15 mumol/cm hr) and intraluminal pressure (6-22 mm Hg). Increases in pressure (6-30 mm Hg) at constant perfusion rate (3 ml/min) did not change alkalinization. The effect of perfusion rate on alkalinization was rapid, reversible, and could be repeated several times. It was unaffected by indomethacin (10 mg/kg subcutaneously) or tetrodotoxin (1 mg/ml in perfusate). A limited in vitro study at two flow rates (0.3 and 22 ml/min) showed a similar enhancement of alkalinization. It is concluded that the rate of alkalinization is increased by raising the perfusion rate of the lumen both in vivo and in vitro. The mechanism remains to be established but may involve the reduction of a diffusion barrier between the mucosa and luminal bulk fluid. These results may have implications for the movement of other substances across intestinal segments.

Acid-Base Equilibrium↗
PubMed1985

The action of two mast cell stabilising agents and verapamil on rat gastric acid secretion in vitro.

The actions of two mast cell stabilising agents, FPL 52694 and disodium cromoglycate and the Ca2+ channel antagonist verapamil on acid secretion by the rat isolated stomach have been studied. FPL 52694 (1-5 mM) in the serosal medium stimulated acid secretion. This was antagonised by prostaglandin E2 but not by atropine, metiamide, propranolol or tetrodotoxin. FPL 52694 (1-5 mM) in the mucosal medium had an inhibitory effect on basal acid secretion and that stimulated by pentagastrin and histamine. The inhibition reversed only slowly after removal of FPL 52694. Disodium cromoglycate and serosal application of verapamil had no significant effects on acid output. Removal of calcium from the bathing solutions and mucosal verapamil inhibited basal secretion. Topically applied, FPL 52694 is a potent inhibitor of acid secretion in vitro. This effect may involve an action upon the availability of calcium to the tissue. The stimulatory effects of serosal FPL 52694 are discussed in relation to previous in vivo findings.

Animals↗
PubMed1984

Observations on the effects of CO2-laser on rat myocardium.

The effect of CO2-laser burn on rat myocardium was studied to evaluate a hypothesis developed by Mirhoseini and Cayton that infarcted myocardium may be revascularized by establishing an alternative circulation from a ventricle to the coronary arteries by means of laser channels burned through the myocardium. The hearts of 22 rats were examined histologically for a period ranging from a few minutes to 50 days after CO2 laser was applied to the myocardium. The laser initiated an intense inflammatory response in the myocardium adjacent to the target site. The authors believe that the inflammatory response, observed in this study to the Biophy-Las 80 surgical laser, must be reduced if laser is to be an effective means of myocardial revascularization.

Animals↗
PubMed1984

The effect of sympathomimetic agents on gastric acid secretion in rats.

Beta-adrenoceptor agonists have been reported to inhibit gastric acid secretion in vivo but their site and mode of action is uncertain. A study of the effects of such agents on acid secretion in the rat has been made using both an in vivo preparation and an in vitro one where possible effects due to neural, hormonal or cardiovascular actions of beta-agonists are avoided. In conscious rats with Heidenhain pouches, isoprenaline (40 micrograms kg-1h-1) inhibited the response to pentagastrin (20 micrograms kg-1h-1). This inhibition was abolished by propranolol (2 mg kg-1) and butoxamine (8 mg kg-1) and partially reversed by practolol (8 mg kg-1). Propranolol alone (2 mg kg-1) significantly increased the response to pentagastrin in the pouch rats but butoxamine and practolol (both at 8 mg kg-1) and the inactive isomer (+)-propranolol were without effect on the pentagastrin response. In the rat isolated stomach preparation isoprenaline, salbutamol, salmefamol , adrenaline and nor-adrenaline all stimulated acid output over the range 2 X 10(-7) to 10(-5)M. These responses were antagonised by propranolol (2 X 10(-5)M), pindolol and timolol (10(-6)M) but only nor-adrenaline stimulated secretion was inhibited by the selective antagonists practolol, atenolol, butoxamine and ICI 118551. In vitro responses to beta-adrenoceptor agonists were not antagonised by atropine (10(-5)M), metiamide (10(-4)M) or prostaglandin E2 (10(-5)M).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Bovine normal peripheral nerve and nerve sheath tumour in explant culture.

When bovine normal nerve and nerve sheath tumours were cultured using explant techniques, the same morphological cell types were seen:thin bipolar cells with bulging nuclei;found refractile cells; large quadrangular cells; variable polar, wide-processed cells. However, differences in the pattern of cell growth and the proportions of morphological cell types occurred between normal and tumour nerve. The bovine nerve sheath tumours cultured showed a range of histological areas which did not appear to affect the pattern of cell growth in culture or the cell types present. Antoni type A tissue was prominent in many explant blocks and probably gave rise to most cell growth. On comparison with human schwannomas maintained in explant culture, bovine nerve sheath tumours appeared to have a similar range of morphological cell types. Although suggestions for the origin of human schwannomas have been made on the basis of cell morphology, it was felt that morphology alone did not allow speculation on the origin of cells present in bovine nerve sheath tumour explant cell growth.

Animals↗
PubMed1978

A light microscopic study of bovine peripheral nerve sheath tumours.

Peripheral nerve sheath tumours from 66 cattle were classified as schwannomas and neurofibromas. Bovine neurofibromatous tissue probably represents a dysplasia whilst bovine schwannomas are true neoplastic growths. Bovine schwannomas probably develop from neurofibromatous nerve and the two entities may represent parts of a single pathological condition.

Animals↗
PubMed1978

The ultrastructure of bovine peripheral nerve sheath tumours.

Bovine peripheral nerve sheath tumours from 30 cattle were similar ultrastructurally to human schwannomas and neurofibromas. Bovine neurofibromatous tissue had large amounts of extracellular material, primarily collagen and electron lucent granular material. The principal cells had basal laminae and a disorganized proliferation of the plasmalemma. Axons were consistently seen and were surrounded by the plasmalemma of principal cells. The principal cells seemed to be Schwann cells or variants of them. Bovine schwannomas had areas similar to Antoni type A tissue with sparse extracellular material, few, if any, axons, and an apparent organized layering of cytoplasmic processes clad in a basal lamina. Cell nuclei often formed palisades. The principal cells in bovine schwannomas might be derived either from Schwann cells or perinuerial cells. Bovine schwannomas appeared together with bovine neurofibromatous tissue in affected nerves.

Animals↗
PubMed1973

Equilibrium of nucleotides in frog sartorius muscle during an isometric tetanus at 20 degrees C.

1. The concentrations of creatine, phosphorylcreatine (PC), ATP, ADP, AMP and IMP have been measured in frog sartorius muscles at 20 degrees C during isometric tetani lasting from 0.5 to 12 sec. Each muscle was tetanized once only for the chosen duration. The muscles were poisoned with iodoacetic acid and nitrogen to prevent oxidative and glycolytic activity.2. The rate of PC splitting decreased exponentially with the duration of the tetanus (alpha = 0.16 sec(-1)). Net ATP splitting began after 2 sec, accompanied by an increase in AMP and ADP; inosine monophosphate (IMP) also appeared both earlier and faster than adenosine monophosphate (AMP).3. On the basis of two equilibrium reactions, the Lohmann and myokinase reactions, the concentration of adenosine nucleotides should be a function of the ratio creatine/phosphorylcreatine.4. The agreement between nucleotide concentrations predicted by this equilibrium hypothesis and those observed experimentally was good provided it was assumed that 90% of the acid-labile ADP found in resting muscle was bound in vivo and remained so throughout the tetanus. The validity of this assumption is discussed.5. The IMP concentration was an exponential function of the ratio creatine/phosphorylcreatine.

Adenine Nucleotides↗
PubMed1973

Energy balance in frog sartorius muscle during an isometric tetanus at 20 degrees C.

1. Changes in the concentrations of ATP, ADP, AMP, IMP, creatine and phosphorylcreatine (PC) have been measured in frog sartorius muscles after different periods of isometric stimulation at 20 degrees C. The heat production was measured in parallel experiments with a thermopile of the Hill-Downing type.2. Muscles were either in O(2) and unpoisoned or in N(2) and poisoned with iodoacetic acid to prevent aerobic and glycolytic recovery processes.3. Poisoning did not appear to alter the heat production of these muscles and had little effect on the tension for up to 8 sec tetanus.4. The break-down of high-energy phosphates ( approximately P) during contraction was faster in the poisoned muscles. Normal muscles were thus able to resynthesize high energy phosphates during the contraction. The resynthesis began at its maximum rate; part of it was probably due to glycolytic activity.5. During the first 2 sec of contraction (poisoned muscles), the only net reaction was an hydrolysis of PC, with an apparent enthalpy change of -8.3 kcal/mole. During longer contractions, the PC hydrolysis was accompanied by a net ATP hydrolysis and appearance of AMP and IMP.6. For the first 2 sec of contraction in the poisoned muscles, the observed heat agreed with that expected from the observed chemical changes multiplied by their molar enthalpy changes. After 2 sec, the observed heat was greater than that expected. At 12 sec this excess was about 74 mcal/g. Possible explanations for this discrepancy are discussed.

Adenine Nucleotides↗
PubMedDate not supplied

Immune-mediated neutropenia suspected in five dogs.

Five cases of suspected immune-mediated neutropenia in dogs are described. Clinical signs varied depending on whether the animals had a systemic infection or concurrent immune-mediated disease. Patients were diagnosed by excluding other causes of neutropenia, supportive bone marrow aspirate findings, an initial favourable response to corticosteroid administration in four of the cases, and concurrent immune-mediated disease. Four of the dogs were receiving medications at the time of diagnosis, and immune-mediated neutropenia secondary to drug therapy cannot be excluded. This study shows that appropriate immunosuppressive treatment can lead to a favourable outcome, however, care is required to avoid adverse effects associated with corticosteroid use. It is also imperative that medications are not withdrawn abruptly as a second remission may not always be achievable.

Animals↗