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R J Willis

Publications and source records attributed to R J Willis.

17 recordsLinked to original sources
PubMed1992

Critical micelle concentration and hemolytic activity--a correlation suggested by the marine sterol, halistanol trisulfate.

The marine natural product, halistanol trisulfate, has a relatively low critical micelle concentration of 0.001% m/v (14.5 microM) and strong hemolytic potency with an EC50 of 0.00046% m/v (6.67 microM). As expected of a detergent, it inhibits the growth of gram-positive but not gram-negative bacteria. The hemolytic activity of halistanol trisulfate and other detergents has been shown to correlate with critical micelle concentration. This correlation may have important implications in the mechanism of membranolytic bioactivity.

Animals↗
PubMed1991

Cytosolic free magnesium in stimulated, hypoxic, and underperfused rat heart.

The aim of this study was to determine whether acute changes in [Mg2+]free occur during increased hydrolysis of cytosolic ATP, and whether these changes were of sufficient magnitude to be involved in the modulation of myocardial metabolism. 31P-NMR was used to estimate free cytosolic Mg2+ levels ([Mg2+]free) during hypoxia, isoproterenol stimulation, and graded low-flow ischemia in crystalloid perfused, isovolumic rat hearts. Cytosolic [Mg2+]free was calculated to be 0.73 +/- 0.12 mM in control hearts (100 mmHg hydrostatic pressure, 95% O2, n = 18). Cytosolic [Mg2+]free increased gradually during 10 min periods of hypoxia (65%, 50%, 35%, 5% O2), and 20 min infusions of isoproterenol (0.4, 3.0, 75 nM), to maximum values greater than 250% of control (P less than 0.05). During 8 min periods of graded low-flow ischemia (12.0, 7.2, 5.3, 3.4, and 1.6 ml/min/g), [Mg2+]free did not change significantly. [Mg2+]free displayed an inverse linear correlation with total cytosolic [ATP] during isoproterenol infusion (r = 0.87), and an exponential correlation during hypoxia (r = 0.82). The data indicate that acute changes in cytosolic [Mg2+]free can occur during conditions of net ATP hydrolysis although changes in ATP alone do not appear to be solely responsible for the changes in [Mg2+]free. Since the magnitude of the changes in [Mg2+]free are sufficient to alter equilibria of enzymes such as creatine kinase and myokinase, it is possible that these changes are involved in the acute modulation of myocardial metabolism.

Adenosine Triphosphate↗
PubMed1990

Behaviour of energy metabolites and effect of allopurinol in the "stunned" isovolumic rat heart.

The pathogenesis of post-ischaemic depression of contractility in myocardium was examined in isovolumic rat heart. 31P-NMR was used to monitor changes in ATP, creatine phosphate (CrP), inorganic phosphate (Pi), and [H+] during brief periods of ischaemia and reperfusion with and without allopurinol treatment. During 5, 10, or 15 min of total global ischaemia, the decline in function (rate-pressure product) correlated inversely with [Pi] (r = 0.92, P less than 0.01). Cardiac function exhibited a slow progressive recovery during 20 min of reperfusion, ultimately reaching only 85%, 78%, and 69% of its pre-ischaemic value following 5, 10, and 15 min of global ischaemia respectively. Following each ischaemic period [ATP], [CrP], [Pi], and [H+] all recovered to control levels within 5-10 min of initiating reperfusion. Allopurinol (2 mM) treatment of hearts made ischaemic for 15 min significantly improved contractile recovery to 89 +/- 7%. Allopurinol also exhibited significant anti-arrhythmic activity during the reperfusion period, decreasing the incidence of premature contractions and the duration of tachy-arrhythmias. Allopurinol had no effect on the final repletion of [ATP] and [CrP], or the recovery of [Pi] and [H+], although the rate of ATP repletion was elevated in the initial 5 min of reperfusion. These results show that neither depletion of the cytosolic high-energy phosphate pool, nor sustained elevations in [Pi] or [H+] are important in the production of post-ischaemic contractile impairment. The beneficial action of allopurinol suggests that xanthine oxidase derived oxygen free-radicals may be involved in the sustained contractile dysfunction following brief ischaemic episodes.

Adenosine Triphosphate↗
PubMed1990

Relation between the O2 supply:demand ratio, MVO2, and adenosine formation in hearts stimulated with inotropic agents.

Mooted controllers of adenosine formation in heart are the oxygen supply:demand ratio, myocardial oxygen consumption (MVO2), the cytosolic phosphorylation potential (log[ATP]/[ADP][Pi]). The relationship between these parameters and purine release (adenosine + inosine) into the venous effluent was examined in isovolumic rat hearts perfused at 20 and 12 mL.min-1.g-1 with a glucose containing crystalloid buffer and stimulated with inotropic agents (isoproterenol, norepinephrine, 3-isobutyl-1-methylxanthine, and ouabain). The oxygen supply:demand ratio and MVO2 were continuously determined using an oxygen electrode to monitor oxygen supply and consumption. The phosphorylation potential was calculated from phosphorus metabolite levels determined by 31P-NMR spectroscopy and HPLC analysis. Left ventricular function was assessed as the rate-pressure product. All inotropic agents increased the rate-pressure product, with increases in function being greater in the hearts perfused at 20 mL.min-1.g-1. MVO2 was linearly related to the rate-pressure product at each flow rate; however, the hearts perfused at 20 mL.min-1.g-1 exhibited approximately twofold greater MVO2 values for similar rate-pressure product values. All inotropic agents increased adenosine release into the venous effluent. While there was a significant linear relation between adenosine formation and MVO2 in hearts perfused at both flow rates and stimulated with drugs, the relations differed with adenosine release being approximately fourfold greater in hearts perfused at 12 mL.min-1.g-1 under similar conditions of MVO2. Adenosine formation correlated exponentially with the ratio of oxygen supply:demand under all conditions (r = 0.97) and the relation did not differ significantly between hearts perfused at different rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1990

Adenosine formation and energy metabolism: a 31P-NMR study in isolated rat heart.

Temporal and quantitative relations between cytosolic energy metabolism, adenosine efflux, and coronary flow were examined during 10 min of isoproterenol (ISO) infusion (60 nM) or hypoxia (5% O2) in isolated isovolumic rat heart. Myocardial metabolism was monitored using 31P-nuclear magnetic resonance spectroscopy, and venous effluent was collected and assayed for adenosine. During ISO infusion, coronary flow increased to approximately 170%, and [ATP]/[ADP] [Pi] (cytosolic phosphorylation potential) declined to less than 25% of preinfusion levels, respectively (P less than 0.001). During hypoxia, coronary flow increased to 190%, and [ATP]/[ADP] [Pi] declined to less than 25% of normoxic levels (P less than 0.001). Release of adenosine into the coronary venous effluent increased greater than 10-fold and displayed significant inverse linear correlations with log[ATP]/[ADP] [Pi] and positive linear correlations with free cytosolic [AMP] and coronary flow during ISO infusion and hypoxia. Adenosine deaminase (ADA) treatment reduced coronary vasodilation by approximately 30% during ISO infusion and 40% during hypoxia (P less than 0.001) and augmented chronotropic and inotropic responses to ISO infusion (P less than 0.01). Infusion of ADA potentiated changes in [ATP]/[ADP] [Pi] and [AMP] observed during ISO infusion and hypoxia (P less than 0.05). These results indicate that 1) endogenous adenosine mediates metabolic vasodilation in the heart, 2) adenosine modulates the response of isolated myocardium to catecholamines, 3) myocardial adenosine formation appears to be linked to cytosolic metabolism via changes in [ATP]/[ADP] [Pi] and [AMP], and 4) endogenous adenosine provides a significant, metabolically beneficial action in isolated hearts during hypoxia and inotropic stimulation.

Adenosine↗
PubMed1989

5'-Nucleotidase activity and adenosine formation in stimulated, hypoxic and underperfused rat heart.

Changes in 5'-nucleotidase activity were calculated on the basis of alterations in ATP, ADP, phosphocreatine, Pi, Mg2+, IMP and AMP, determined by using 31P n.m.r. spectroscopy and h.p.l.c., during isoprenaline infusion, graded hypoxia and graded underperfusion in isolated rat heart. Calculated activity changes were compared with the total efflux of purines (adenosine + inosine + hypoxanthine) in order to assess the involvement of various 5'-nucleotidases in formation of adenosine. Purine efflux exhibited an exponential relation with cytosolic [AMP] during isoprenaline infusion and hypoxia (r = 0.92 and 0.95 respectively), supporting allosteric activation of 5'-nucleotidase under these conditions. Purine efflux displayed a linear relation with cytosolic [AMP] during graded ischaemia (r = 0.96), supporting substrate regulation in the ischaemic heart. The calculated activities of membrane-bound ecto-5'-nucleotidase were similar to the observed relations between purine efflux and cytosolic [AMP] in all hearts. The calculated activities of the ATP-activated cytosolic and lysosomal enzymes and of the ATP-inhibited cytosolic 5'-nucleotidase could not explain the observed release of purines under the conditions examined. These results indicate that the kinetic characteristics of the membrane-bound ecto-enzyme are consistent with an important role in the formation of extracellular adenosine, whereas the characteristics of the other 5'-nucleotidases are inconsistent with roles in adenosine formation under the conditions of the present study.

5'-Nucleotidase↗
PubMed1989

Effect of inotropic stimulation on cytosolic Mg2+ in isolated rat heart: a 31P magnetic resonance study.

Alterations in cytosolic metabolites and [Mg2+]i were monitored using 31P magnetic resonance spectroscopy during inotropic stimulation of isolated rat heart [10 nM isoproterenol, 0.6 microM isobutyl-1-methylxanthine (IBMX), 5 microM ouabain]. All drugs significantly elevated contractile function (rate-pressure product) and MVO2 by approximately 100-150% (P less than 0.001), decreased cytosolic [creatine phosphate] ([CrP]) and [ATP] (approximately 65 and 80% of control values, respectively) (P less than 0.001), increased [Pi] to more than 180% of pretreatment values, and decreased [H+] by less than 15% (P less than 0.05). A significant relative shift in the alpha-P and beta-P resonances of ATP (P less than 0.01) occurred with inotropic stimulation. [Mg2+]i calculated on the basis of these shifts was found to be 0.78 +/- 0.1 mM in control hearts, and increased to maxima of 1.9 +/- 0.2, 2.0 +/- 0.2, and 2.9 +/- 0.2 mM during infusion of isoproterenol, IBMX, and ouabain, respectively. Changes in [Mg2+]i correlate with cytosolic [ATP] + [CrP] in all hearts (r = 0.89, 0.91, and 0.88 in isoproterenol-, IBMX-, and ouabain-treated hearts, respectively). The significantly higher [Mg2+]i with ouabain infusion (P less than 0.01) at similar workloads and [ATP] + [CrP] supports the proposal that a ouabain-inhibited Mg2+ pump exists in the plasma membrane. The data support acute changes in [Mg2+]i during alterations in inotropic state that may be important in modulating metabolic and contractile function.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Adenosine production and energy metabolism in ischaemic and metabolically stimulated rat heart.

Adenosine may modulate blood flow and electrical activity in heart in response to changes in myocardial energy metabolism. In the present study, 31P NMR spectroscopy was used to examine the relation between cytosolic phosphate metabolite levels and release of adenosine into the venous effluent of isovolumic heart during graded low-flow ischaemia or metabolic stimulation with isoproterenol. When coronary flow rate was varied in steps between 1.6 and 12 ml/min/g, cytosolic ATP levels did not change significantly but the phosphorylation potential exhibited a linear correlation with flow rate below approximately 7 ml/min/g. Purine release (adenosine and inosine) correlated linearly with the cytosolic phosphorylation potential and free AMP concentration. Metabolic stimulation of hearts with isoproterenol (0.4, 3.0, and 60 nM), produced a significant fall in cytosolic ATP levels and decreased the cytosolic phosphorylation potential. Purine release in these hearts increased exponentially as the cytosolic phosphorylation potential dropped, and as cytosolic free AMP increased. These results support a link between the phosphorylation potential and the mechanism of adenosine production during ischaemia and metabolic stimulation. Presumably, this link is the activity of the enzyme 5'-nucleotidase, which is responsible for converting AMP to adenosine, together with the concentration of its substrate, AMP. In low-flow ischaemia, cytosolic AMP may control adenosine formation. With isoproterenol stimulation, a more complex relationship exists, indicating possible allosteric regulation of the enzyme(s) responsible for adenosine formation, in addition to changes in AMP concentration.

5'-Nucleotidase↗
PubMed1989

Effects of adenosine antagonism and beta-blockade during low-flow ischaemia in rat heart.

1. The effects of adenosine antagonism (8-phenyltheophylline) and beta-blockade (1-propranolol) were examined during low-flow ischaemia (0.5 mL/min per g for 20 min) in rat heart. 2. Myocardial adenosine release, heart rate, and left ventricular developed pressure were monitored to determine whether endogenous adenosine affected ischaemic function directly, and/or via interaction with endogenous catecholamines. 3. Adenosine release increased more than 10-fold during low-flow ischaemia. Release displayed a phasic pattern, with maximal release occurring at 10 min. Ischaemia produced bradycardia (-180 beats/min) which was reduced by 8-phenyltheophylline infusion (P less than 0.001, n = 10). Adenosine antagonism also significantly increased left ventricular developed pressure in the initial 5 min of ischaemia (P less than 0.001, n = 10). 4. beta-blockade alone was without effect in ischaemic hearts, however, beta-blockade significantly reduced the initial increases in heart rate and developed pressure observed during infusion of 8-phenyltheophylline (P less than 0.001, n = 10). The effect of beta-blockade was transient, occurring in the initial 5-6 min of ischaemia. 5. The data indicate that endogenous adenosine directly mediates greater than 30% of the bradycardia associated with low-flow ischaemia, and that endogenous adenosine inhibits the release and/or the effects of endogenous catecholamines produced during the initial 5-6 min of ischaemia.

Adenosine↗
PubMed1978

Gas identity hazards and major contamination of the medical gas system of a new hospital.

During commissioning of the medical gas system of a new hospital, fourteen connection defects were found; six of these were potentially lethal cross-connections. A major contaminant was also detected throughout the medical gas system. The methods of testing a new medical gas system described in this report highlight the need for up-grading of existing standards.

Australia↗
PubMed1978

Red cell damage induced by peroxidized microsomes: the relationship between hemolytic activity and peroxide content.

Rat red blood cells will hemolyze if they are present in vitro in mixtures of rat liver microsomes in which lipid peroxidation has been initiated by NADPH. Recent work from this laboratory indicated that a toxic factor not having radical properties could be generated from the lipids of the peroxidizing microsomes. This toxic factor produced prelytic damage in rat red blood cells. In this communication we show that if Ca(++)-aggregated microsomes are first peroxidized and then sedimented by centrifugation, the resuspended peroxidized microsomes are capable of hemolyzing red cells in the absence of any further microsomal lipid peroxidation. This result shows conclusively that the microsomal lipid peroxidation step can be separated from the attack on red cells leading to frank hemolysis. Furthermore, lipids extracted from the peroxidized microsomes with chloroform-methanol account quantitatively for the degree of hemolysis produced. The active hemolytic material could not be detected in resuspended microsomal centrifugates obtained during the first 10 minutes of NADPH-stimulated microsomal lipid peroxidation. It appeared rapidly after 10 minutes. It was maximal at 20 minutes, and fell to a low level of activity by 60 minutes. Peak hemolytic activity correlated with peak generation of lipid soluble peroxides. High, but less than maximal levels of peroxides appearing at 10 minutes did not cause hemolysis, and high, but less than maximal levels remaining at 60 minutes were only weakly hemolytic. The extracted lipoidal material with hemolytic potency is more reactive than hydrogen peroxide in a peroxide assay.

Animals↗
PubMed1977

Hemolytic activity of a lipid material obtained from peroxidized microsomes.

Lipid peroxidation was induced in rat liver microsomes by the addition of NADPH. When mixed with red cells in the presence of EDTA, these peroxidized microsomes caused hemolysis. All of the hemolytic activity of peroxidized microsomes could be extracted with lipid solvents and recovered as an aqueous lipid emulsion.

Animals↗
PubMed1976

Extracellular ascorbic acid in lung.

Fifty percent of the ascorbic acid content of sliced rat lung was released from the tissue to the media within a few minutes by either washing or incubating the slices with Krebs-phosphate solution. Measurement of the lactate dehydrogenase and potassium content of the medium after incubating lung slices for 5 min showed that about 20% of the cells were damaged by slicing. Sephadex chromatography of tissue extracts prepared from washed lung slices showed that none of the ascorbic acid in these slices were bound to protein. Also, metabolic poisons were shown to deplete the ascorbic acid content of washed lung slices. Approx. 57% of the lung ascorbic acid of guinea pigs that had been supplemented with ascorbic acid and 78% of the lung ascorbic acid of ascorbic acid-deficient guinea pigs were found in the medium when lung slices from these animals were incubated with Krebs-phosphate solution. These results were taken to indicate the presence of an extracellular pool of ascorbic acid in lung which is maintained even during scurvy.

Animals↗
PubMed1975

Transport of ascorbic acid in perfused rat lung.

Rat lungs were perfused by recycling Krebs-bicarbonate solution in an apparatus which allowed negative pressure ventilation of the lungs. After addition of either reduced or oxidized ascorbic acid to the perfusion fluid serial samples were taken over 60 min and assayed for ascorbic acid. At the end of perfusion, lungs were assayed for ascorbic acid. The results show that reduced ascorbic acid was taken up by the lung and concentrated in the tissue. No appreciable transport of oxidized ascorbic acid was measured.

Animals↗
PubMed1975

Pulmonary edema and ascorbic acid loss.

Loss of ascorbic acid from lung and pulmonary edema were produced in mice by intravenous injection of either adrenaline or noradrenaline (5 mumol/kg). While adrenalectomy performed before noradrenaline administration reduced the degree of pulmonary edema, a prior dose of hexamethonium accentuated this effect. Given alone, hexamethonium caused both loss of ascorbic acid and pulmonary edema. The results show that although endogenous catecholamines can potentiate the pulmonary edema produced by either adrenaline or noradrenaline, they play no specific role in the ascorbic acid loss. The evidence suggests that lung ascorbic acid levels are decreased following the development of pulmonary edema, irrespective of how it was caused.

Adrenal Glands↗