A Striking Confluence Between Theory and Observations of High-Mass X-ray Binary Pulsars.

We analyse the most powerful X-ray outbursts from neutron stars in ten Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray sources. Most of the outbursts rise to L max which is about the level of the Eddington luminosity, while the rest and more powerful outbursts also appear to recognize that limit when their emissions are assumed to be anisotropic and beamed toward our direction. We use the measurements of pulsar spin periods P S and their derivatives P ˙ S to calculate the X-ray luminosities L p in their faintest accreting ("propeller") states. In four cases with unknown P ˙ S , we use the lowest observed X-ray luminosities, which only adds to the heterogeneity of the sample. Then we calculate the ratios L p /L max and we obtain an outstanding confluence of theory and observations from which we conclude that work done on both fronts is accurate and the results are trustworthy: sources known to reside on the lowest Magellanic propeller line are all located on/near that line, whereas other sources jump higher and reach higher-lying propeller lines. These jumps can be interpreted in only one way, higher-lying pulsars have stronger surface magnetic fields in agreement with empirical results in which P ˙ S and L p values were not used.

Retrograde Accretion Disks in High-Mass Be/X-ray Binaries.

We have compiled a comprehensive library of all X-ray observations of Magellanic pulsars carried out by XMM-Newton, Chandra, and RXTE in the period 1997-2014. In this work, we use the data from 53 high-mass Be/X-ray binaries in the Small Magellanic Cloud to demonstrate that the distribution of spin-period derivatives vs. spin periods of spinning-down pulsars is not at all different than that of the accreting spinning-up pulsars. The inescapable conclusion is that the up and down samples were drawn from the same continuous parent population, therefore Be/X-ray pulsars that are spinning down over periods spanning 18 years are in fact accreting from retrograde disks. The presence of prograde and retrograde disks in roughly equal numbers supports a new evolutionary scenario for Be/X-ray pulsars in their spin period-period derivative diagram.

Haptic-Assisted Target Acquisition in a Visual Point-and-Click Task for Computer Users with Motion Impairments.

Haptic assistance is the process of using force feedback to aid the operator in human-computer interaction (HCI). This may take the form of guiding the operator toward a target or assisting them in its selection. Haptic feedback has previously been investigated to assist motion-impaired computer users; however, limitations of previous 2 DOF haptic target acquisition techniques such as gravity wells and high-friction-targets have hampered progress. In this paper, two new haptic-assistive techniques are presented that utilize the 3 DOF capabilities of the Phantom Omni to produce assistance that is designed specifically for motion-impaired computer users. These include haptic cones and V-shaped funnels. To evaluate the effectiveness of the new haptic techniques, a series of point-and-click experiments were undertaken in parallel with cursor analysis to compare the levels of performance. The task required the operator to produce a predefined sentence on the Windows-On-Screen Keyboard. The results of the study prove that higher performance levels can be achieved using techniques that are less constricting than traditional assistance and without many of the drawbacks. Haptic cones produced the most significant results when compared to an unassisted interface with a mean improvement of 53 percent in the number of missed clicks and 145 percent improvement in throughput.

Applying forces to elastic network models of large biomolecules using a haptic feedback device.

Elastic network models of biomolecules have proved to be relatively good at predicting global conformational changes particularly in large systems. Software that facilitates rapid and intuitive exploration of conformational change in elastic network models of large biomolecules in response to externally applied forces would therefore be of considerable use, particularly if the forces mimic those that arise in the interaction with a functional ligand. We have developed software that enables a user to apply forces to individual atoms of an elastic network model of a biomolecule through a haptic feedback device or a mouse. With a haptic feedback device the user feels the response to the applied force whilst seeing the biomolecule deform on the screen. Prior to the interactive session normal mode analysis is performed, or pre-calculated normal mode eigenvalues and eigenvectors are loaded. For large molecules this allows the memory and number of calculations to be reduced by employing the idea of the important subspace, a relatively small space of the first M lowest frequency normal mode eigenvectors within which a large proportion of the total fluctuation occurs. Using this approach it was possible to study GroEL on a standard PC as even though only 2.3% of the total number of eigenvectors could be used, they accounted for 50% of the total fluctuation. User testing has shown that the haptic version allows for much more rapid and intuitive exploration of the molecule than the mouse version.

A novel dephosphorylation-activated conductance in a mouse renal collecting duct cell line.

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited renal diseases. It is associated with the progressive development of renal tubular cysts, which may subsequently lead to renal failure. Studies into the genetic basis of ADPKD have identified two genes, PKD1 and PKD2, that are mutated in ADPKD patients. The PKD1 and PKD2 genes encode for two different proteins, TRPP1 and TRPP2. Previous studies have demonstrated the presence of both TRPP1 and TRPP2 in the renal collecting duct cell line M8. The aim of the following study was to investigate the functional properties of cation currents in these cells and to examine the effect of overexpression of TRPP1 using a transgenic cell model (M7). In M8 cells, initial whole cell currents were low. However, over time there was activation of a flow-sensitive current, which was inhibited by gadolinium (I(Gd)). The I(Gd) was more selective for cations over anions, but did not discriminate between monovalent cations and was Ca2+ permeable. Activation of I(Gd) was dependent on the presence of Ca2+ and also required dephosphorylation. The protein phosphatase 2A inhibitor okadaic acid prevented activation of I(Gd), suggesting that protein phosphatase 2A plays an important role in channel activation. The properties and magnitude of I(Gd) were unaffected in M7 cells, suggesting that overexpression of TRPP1 was without effect. I(Gd) was selectively inhibited by an antibody raised against the C-terminus of TRPP2. However, its selectivity profile was different to TRPP2, suggesting that it is attributable to a TRPP2-like channel or a TRPP2-containing heteromeric channel. In conclusion, these data describe the functional identification of a novel dephosphorylation- and flow-activated TRPP2-related channel in mouse collecting duct cells.

Plasma nitrate accumulation during the development of pacing-induced dilated cardiac myopathy in conscious dogs is due to renal impairment.

Heart failure is associated with an increase in plasma nitrate and nitrite (NOx). To date there is still some controversy regarding the causes of nitrate accumulation during the development of heart failure. The goal of this study was to analyze the underlying mechanisms that cause accumulation of plasma nitrates during the development of heart failure in dogs. Dogs were chronically instrumented for measurement of hemodynamics and renal function. Hearts were paced initially at 210 bpm for 3 weeks and then at 240 until the development of heart failure. Hemodynamics, renal function, renal blood flow, arterial blood gases, hemoglobin, plasma and urine NOx levels, and creatinine levels were measured weekly. Heart failure was assessed by hemodynamic alterations, physical signs such as lethargy, ascites, cachexia, and postmortem evidence of cardiac hypertrophy. LVSP (from 127 +/- 3 to 106 +/- 3 mmHg), LV dP/dt (from 2658 +/- 173 to 1439 +/- 217 mmHg/s), MAP (from 101 +/- 1.9 to 83 +/- 1.8 mmHg) fell, whereas LVEDP tripled (from 6.4 +/- 0.9 to 20 +/- 2.6 mmHg), and heart rate rose (from 101 +/- 4.2 to 117 +/- 6.3 bpm), all changes P < 0.05. RBF (from 146 +/- 10 to 96 +/- 9.9 ml/min), urine output (V) (from 0.26 +/- 0.02 to 0.16 +/- 0.02 ml/min), GFR (from 63 +/- 1.8 to 49 +/- 2 ml/min), and Na excretion (from 45 +/- 4.5 to 14 +/- 4.6 microEq/min) all decreased (P < 0.05), whereas RVR increased (from 0.68 +/- 0.05 to 0.94 +/- 0.1 mmHg/ml/min). These changes took place during a rise in plasma NOx (from 3.7 +/- 0.5 to 16+/-3.3 microM), a decrease in urine NOx (from 33 +/- 9.9 to 8.1 +/- 4.9 microM), and a concurrent increase in NOx reabsorption (from 221 +/- 31 to 818 +/- 166 nmol/min). There was a direct correlation between the increase in plasma NOx levels and an increase in filtered load (r(2) = 0.97, P = 0.02), a negative correlation between NOx levels and NOx excretion (r(2) = 0.65 P < 0.09), and a direct correlation between plasma NOx levels and NOx reabsorption (r(2) = 0.97, P = 0.02). These results indicate that elevated plasma NOx during heart failure are most likely the result of an impairment of the renal function and not increased NOx production. Furthermore, without knowing changes in renal function the measurement of plasma NOx in and of itself is a meaningless index of NO formation.

Role of nitric oxide in the control of cardiac oxygen consumption in B(2)-kinin receptor knockout mice.

The aim of this study was to determine whether bradykinin, the angiotensin-converting enzyme inhibitor ramiprilat, and the calcium-channel antagonist amlodipine reduce myocardial oxygen consumption (MV(O2)) via a B(2)-kinin receptor/nitric oxide-dependent mechanism. Left ventricular free wall and septum were isolated from normal and B(2)-kinin receptor knockout (B(2) -/-) mice. Myocardial tissue oxygen consumption was measured in an airtight chamber with a Clark-type oxygen electrode. Baseline MV(O2) was not significantly different between normal (239+/-13 nmol of O(2). min(-1). g(-1)) and B(2) -/- (263+/-24 nmol of O(2). min(-1). g(-1)) mice. S-nitroso-N-acetyl-penicillamine (10(-7) to 10(-4) mol/L) reduced oxygen consumption in a concentration-dependent manner in both normal (maximum, 36+/-3%) and B(2) -/- mice (28+/-3%). This was also true for the endothelium-dependent vasodilator substance P (10(-10) to 10(-7) mol/L; 22+/-7% in normal mice and 20+/-4% in B(2) -/- mice). Bradykinin (10(-7) to 10(-4) mol/L), ramiprilat (10(-7) to 10(-4) mol/L), and amlodipine (10(-7) to 10(-5) mol/L) all caused concentration-dependent decreases in MV(O2)in normal mice. At the highest concentration, tissue O(2) consumption was decreased by 18+/-3%, 20+/-5%, and 28+/-3%, respectively. The reduction in MV(O2) to all 3 drugs was attenuated in the presence of N(G)-nitro-L-arginine-methyl ester. However, in the B(2) -/- mice, bradykinin, ramiprilat, and amlodipine had virtually no effect on MV(O2). Therefore, nitric oxide, through a bradykinin-receptor-dependent mechanism, regulates cardiac oxygen consumption. This physiological mechanism is absent in B(2) -/- mice and may be evidence of an important therapeutic mechanism of action of angiotensin-converting enzyme inhibitors and amlodipine.

Nitric oxide modulates mitochondrial respiration in failing human heart.

Background-Our objective for this study was to investigate whether nitric oxide (NO) modulates tissue respiration in the failing human myocardium. Methods and Results-Left ventricular free wall and right ventricular tissue samples were taken from 14 failing explanted human hearts at the time of transplantation. Tissue oxygen consumption was measured with a Clark-type oxygen electrode in an airtight stirred bath containing Krebs solution buffered with HEPES at 37 degrees C (pH 7.4). Rate of decrease in oxygen concentration was expressed as a percentage of the baseline, and results of the highest dose are indicated. Bradykinin (10(-4) mol/L, -21+/-5%), amlodipine (10(-5) mol/L, -14+/-5%), the ACE inhibitor ramiprilat (10(-4) mol/L, -21+/-2%), and the neutral endopeptidase inhibitor thiorphan (10(-4) mol/L, -16+/-5%) all caused concentration-dependent decreases in tissue oxygen consumption. Responses to bradykinin (-2+/-6%), amlodipine (-2+/-4%), ramiprilat (-5+/-6%), and thiorphan (-4+/-7%) were significantly attenuated after NO synthase blockade with N-nitro-L-arginine methyl ester (10(-4) mol/L; all P<0.05). NO-releasing compounds S-nitroso-N-acetyl-penicillamine (10(-4) mol/L, -34+/-5%) and nitroglycerin (10(-4) mol/L, -21+/-5%), also decreased tissue oxygen consumption in a concentration-dependent manner. However, the reduction in tissue oxygen consumption in response to S-nitroso-N-acetyl-penicillamine (-35+/-7%) or nitroglycerin (-16+/-5%) was not significantly affected by N-nitro-L-arginine methyl ester. Conclusions-These results indicate that the modulation of oxygen consumption by both endogenous and exogenous NO is preserved in the failing human myocardium and that the inhibition of kinin degradation plays an important role in the regulation of mitochondrial respiration.

Na+/H+ exchange inhibition improves long-term myocardial preservation.

BACKGROUND: Na+/H+ exchange plays an important role in the ionic changes observed during myocardial ischemia and reperfusion. We investigated the cardioprotective efficacy of a selective Na+/H+ exchange inhibitor, 4-isopropyl-3-methylsulfonyl-benzoylguanidin-methanesulfonate (HOE642), in a canine model of long-term heart preservation. METHODS: Canine donor hearts were stored for 24 hours in hyperkalemic crystalloid cardioplegic solution; in cardioplegic solution enriched with HOE642; in cardioplegic solution enriched with HOE642, with donor and recipient treated with HOE642; in standard cardioplegic solution, with donor and recipient treated with HOE642; or in standard cardioplegic solution, with only the recipient treated. After orthotopic transplantation, pressure-volume relationships were obtained and dogs were weaned from bypass. Morphology was studied. RESULTS: Myocardial compliance was well preserved when donor and recipient were treated. These groups had the lowest myocardial water content, and no morphologic signs of irreversible damage. In these groups, weaning from cardiopulmonary bypass was successful in 10 of 10 animals, with a cardiac index around 2 L x min(-1) x m(-2). Only 3 of 5 animals in each of the other three groups could be weaned, with significantly lower cardiac indices. CONCLUSIONS: Treatment with HOE642 in both donor and recipient improves myocardial compliance, postweaning cardiac index, and ultrastructure of donor hearts preserved for 24 hours and orthotopically transplanted.

Role of nitric oxide in the control of renal oxygen consumption and the regulation of chemical work in the kidney.

Inhibition of NO synthesis has recently been shown to increase oxygen extraction in vivo, and NO has been proposed to play a significant role in the regulation of oxygen consumption by both skeletal and cardiac muscle in vivo and in vitro. It was our aim to determine whether NO also has such a role in the kidney, a tissue with a relatively low basal oxygen extraction. In chronically instrumented conscious dogs, administration of an inhibitor of NO synthase, nitro-L-arginine (NLA, 30 mg/kg i.v.), caused a maintained increase in mean arterial pressure and renal vascular resistance and a decrease in heart rate (all P<0.05). At 60 minutes, urine flow rate and glomerular flow rate decreased by 44+/-12% and 45+/-7%, respectively; moreover, the amount of sodium reabsorbed fell from 16+/-1.7 to 8.5+/-1.1 mmol/min (all P<0.05). At this time, oxygen uptake and extraction increased markedly by 115+/-37% and 102+/-34%, respectively (P<0.05). Oxygen consumption also significantly increased from 4.5+/-0.6 to 7.1+/-0.9 mL O2/min. Most important, the ratio of oxygen consumption to sodium reabsorbed increased dramatically from 0.33+/-0.07 to 0.75+/-0.11 mL O2/mmol Na+ (P<0.05), suggesting a reduction in renal efficiency for transporting sodium. In vitro, both a NO-donating agent and the NO synthase-stimulating agonist bradykinin significantly decreased both cortical and medullary renal oxygen consumption. In conclusion, NO plays a role in maintaining a balance between oxygen consumption and sodium reabsorption, the major ATP-consuming process in the kidney, in conscious dogs, and NO can inhibit mitochondrial oxygen consumption in canine renal slices in vitro.

Photobactericidal activity of phenothiazinium dyes against methicillin-resistant strains of Staphylococcus aureus.

The photodynamic antibacterial properties of a closely related series of phenothiazinium dyes were tested against several pathogenic strains of Staphylococcus aureus, four of which were methicillin-resistant. Illumination of the photosensitisers at a fluence rate of 1.75 mW cm-2 generally resulted in the enhancement of antibacterial activity in liquid culture and in greater efficacy than the methicillin analogue flucloxacillin. For methylene blue, dimethyl methylene blue and new methylene blue illumination led to increases in bactericidal activity < or = 16-fold, typically 4-fold. In addition dimethyl methylene blue and new methylene blue were active against epidemic strains of methicillin-resistant Staphylococcus aureus at concentrations lower than that of vancomycin (> or = 0.5 microM).

Localization and determination of infarct size by Gd-Mesoporphyrin enhanced MRI in dogs.

BACKGROUND: Accurate localization and sizing of a myocardial infarction are necessary for clinical decision making and even more in research. Gd-Mesoporphyrin enhanced magnetic resonance imaging (MRI) was recently shown to specifically delineate necrosis in liver tumors, renal and muscle necrosis and myocardial infarction in rats. In this study, we investigated this technique's potential to accurately delineate myocardial infarction in a larger animal species, the dog. METHODS: Myocardial infarction was induced in 8 dogs by ligation of the left anterior descending coronary artery, 4 of which were reperfused after 3 hr Gd-Mesoporphyrin (0.05 mmol/kg) was injected intravenously 210 min after the onset of ischemia (n = 6) or after 24 hr in 2 dogs with non-reperfused infarctions. MRI was performed 10 hr after administration of Gd-Mesoporphyrin. In vivo MRI consisted of EKG-triggered, respiratory gated T1-weighted spin echo and segmented turboFLASH long and short axis measurements. Post-mortem, a spin echo short axis measurement was repeated. Infarct size was determined planimetrically by TTC staining of left ventricular slices. RESULTS: In all instances, there was a very close qualitative agreement between the MRI and TTC defined myocardial infarction. Quantitatively, the linear regression from post-mortem MRI to TTC determined infarct size yielded a result very close to the line of identity (regression coefficient: 0.980 +/- 0.026, p < 0.000001, adjusted R2 = 0.964). CONCLUSION: We conclude that Gd-Mesoporphyrin enhanced MRI is a promising tool for the accurate delineation of myocardial infarction.

Effects of failure of the right side of the heart and increased pulmonary resistance on mechanical circulatory support with use of the miniaturized HIA-VAD displacement pump system.

This experimental study was designed to assess the influence of failure of the right side of the heart or pulmonary hypertension, or both, on the performance of a novel miniaturized left ventricular assist device. In small-sized dogs (n = 50) ischemic global left ventricular failure was induced and support was provided by the HIA-VAD displacement pump (stroke volume 10 or 25 ml) installed as a left ventricular assist device. In three groups of animals (n = 10 each) pulmonary hypertension was created before induction of global left ventricular failure. During left ventricular assist device support temporary ischemic failure of the right side of the heart was induced in four groups of animals (n = 10 each). In the group subjected to left ventricular failure, support with the left ventricular assist device, and right ventricular failure during left ventricular assist, left atrial pressure and cardiac index were significantly lower than in the group subjected to left ventricular failure and left ventricular assist alone (2 +/- 6 versus 11 +/- 6 mm Hg and 1.6 +/- 0.4 versus 1.0 +/- 0.4 L/(min/m2), respectively, p < 0.05). In the group subjected to pulmonary hypertension, left ventricular failure, and left ventricular support, left atrial pressure dropped to values near zero but cardiac index remained unaltered as compared with results with the same regimen without pulmonary hypertension. However, when right ventricular failure was added (that is, pulmonary hypertension, left ventricular failure, left ventricular support, and right ventricular failure during support with the left ventricular assist device) left atrial pressure dropped to negative values (p < 0.05) and cardiac index progressively deteriorated. When, in an additional group of dogs, biventricular support was installed in the latter regimen, circulation was initially well supported but oxygenation deteriorated in 60% of cases. We conclude that (1) adequate right ventricular function was indispensable during support with the left ventricular assist device, (2) the combination of pulmonary hypertension and right ventricular failure led to the "low left ventricular assist device output syndrome," and (3) biventricular mechanical support in the presence of pulmonary hypertension may be complicated by the alveolar leakage syndrome.

The heart-Hemopump interaction: a study of Hemopump flow as a function of cardiac activity.

The Hemopump is a useful left ventricular assist device. Because it is a rotary blood pump, the pump performance is not constant and is dependent on the cardiac cycle. We measured the static flow delivered by the pump at varying pressure heads (delta P) in a mock circulation. These data are compared to the pump performance in vivo. On the basis of these results, 5 sheep were instrumented for continuous Hemopump flow measurement as well as left ventricular and aortic pressure measurements. The Hemopump flow was relayed instantaneously to the pressure head. Low filling and ventricular failing (through intravenous administration of a beta-blocker) conditions were applied. The in vivo measured flows also are pressure head dependent, but the flow curve shows hysteresis resulting in a loop during each cardiac cycle. The in vivo peak flows (delta P = 0) are similar to the in vitro data. The in vivo means flows (delta = 50 mm Hg) are similar to the in vitro data for the lower pump speeds but are less than that at the higher pump speeds (3.74 +/- 0.55 L/min in vivo at Speed 7 versus 4.6 L/min in vitro). Low filling interrupts the delta P-flow loop and reduces flow. In the failing ventricle, delta P increases and flow is reduced. The cannula leaks and results in aortic insufficiency (0.36 +/- 0.05 L/min) when the pump is turned off. Several conclusions have been drawn from these tests: Cardiac activity is beneficial for the pump performance as well as when the aortic pressure curve is nonpulsatile; the longer the systolic phase, the higher the pump flow; the pump should never be turned off in clinical use, and filling is important for the pump's performance.

Captopril and norepinephrine-induced hypertrophy and haemodynamics in rats.

We wished to determine whether pretreatment with captopril, an angiotension-converting enzyme (ACE) inhibitor, modified the myocardial and haemodynamic consequences of chronic administration of norepinephrine (NE) in rats. Administration of NE (0.15 mg kg(-1) h(-1) by an osmotic minipump implanted subcutaneously for 28 days) resulted in left but not right ventricular hypertrophy. Captopril (250 but not 52 mu g kg(-1) h(1) administered for 28 days) significantly attenuated the development of left ventricular hypertrophy (weight of left ventricle to body weight ratio was 0.46 +/- 0.01 0.57 +/- 0.02, 0.53 +/- 0.02, and 0.51 +/- 0.01 for vehicle, NE, and NE plus low and high dose of captopril, respectively). Chronic administration of NE caused significant increases in systolic arterial blood pressure (BP: 194 +/- 11 vs. 130 +/- 6 mm Hg), systolic left ventricular pressure, heart rate (HR: 458 +/- 13 vs. 389 +/- 15 beats/min) and dP dt(-1)(max) P(-1), an index of myocardial contractility (202 +/- 29 vs. 91 +/- 3 s(-1)). Captopril (250 mu g kg(-1) h(-1) for 28 days) significantly reduced diastolic arterial BP (from 86 +/- 6 to 53 +/- 3 mm Hg). Concomitant administration of this dose of captopril together with NE prevented the NE-induced increase in systolic arterial BP but did not modify the increases in HR or dP dt(-1) max P(-1) (261 +/- 41 and 202 +/- 29 s(-1) in captopril and NE vs. NE-alone groups). Acute administration of NE (0.1-10 mu g kg(-1) intravenously, i.v.) produced less marked increases in cardiac contractility and in arterial BP in rats chronically pretreated with NE or NE plus captopril than in animals receiving vehicle or captopril alone. Chronic administration of NE and/or captopril did not significantly modify the haemodynamic effects of the acute administration of calcium chloride. We conclude that administration of captopril at 250 but not 52 mu g kg(-1) h(-1) for 28 days attenuates NE-induced cardiac hypertrophy and that this effect is associated with a decrease in systolic arterial BP. Captopril did not modify the reduced effects of acutely administered NE in rats treated with NE for a prolonged period.

Effects of chronic norepinephrine administration on cardiac function in rats.

We assessed the changes in the contractile response of rat hearts in vivo after chronic exposure to a range of doses of norepinephrine (NE) and determined whether free radical production played a role in these changes. Osmotic minipumps were implanted subcutaneously (s.c.) in male rats and delivered either NE (0.15-0.35 mg/kg/h) or acid saline for 10-28 days. The animals were then anaesthetised and prepared for haemodynamic measurement, and dose-response curves to acutely administered NE and calcium chloride were constructed. We analysed plasma for evidence of free radical activity by measuring the levels of thiobarbituric acid-reactive substances (TBARS). All doses of NE studied produced left, but not right, ventricular hypertrophy. Treatment with 0.25 mg/kg/h NE for 28 days produced signs of distress and, by 10 days, treatment with 0.35 mg/kg/h resulted in 33% mortality. Treatment with the two lower doses, but not the highest dose, of NE resulted in increases in basal left ventricular (LV) maximum rate of pressure generation and a marked increase in systolic, but not diastolic, arterial blood pressure (SBP, DBP). All doses of NE caused reduced responses to acutely administered NE but no marked change in the response to calcium chloride. Levels of plasma free radicals were increased only with the highest dose of NE. Over the concentration range studied, chronic administration of NE to rats causes beta-adrenoceptor downregulation and free radical production was associated only with the administration of a dose of NE that resulted in high mortality.

Effects of the xanthine oxidase system on cardiac function in anaesthetised rats.

This investigation aimed to determine whether contractile dysfunction of the myocardium could be produced upon generation of free radicals in the anaesthetised rat. The enzyme xanthine oxidase, combined with its substrate purine and an iron source, was used to generate free radicals in the venous circulation. The suspended form of xanthine oxidase, with substrate, produced a transient, significant depression in the contractile indices dP dt-1 max and dP dt-1 P-1 and arterial blood pressure, 1146 +/- 87 mm Hg s-1, 9 +/- 1 s-1, and 18 +/- 1 mm Hg, respectively. This could not be attenuated by the enzymatic free radical scavengers superoxide dismutase and catalase. Furthermore, the suspended xanthine oxidase alone or its vehicle were able to produce a similar effect to that of the complete free-radical-generating system. The maximum soluble dose of the crystalline form of the enzyme when employed in the generating system had no effect upon administration despite its production of superoxide radicals in vitro. These results suggest that the haemodynamic effects of the free-radical-generating system containing the suspended form of xanthine oxidase were due to the effects of its vehicle and that the free-radical-generating system containing the crystalline form of the enzyme did not produce sufficient free radicals in vivo to modify myocardial contractility.

The effects of drugs on Sephadex-induced eosinophilia and lung hyper-responsiveness in the rat.

1. Rats given an intravenous injection of Sephadex particles (0.5 mg of G200 in 1 ml of saline) on days 0, 2 and 5 had a blood eosinophilia which was maximal on day 7. 2. On day 7, broncho-alveolar lavage (BAL) fluids taken from the rats contained an increased number of eosinophils and fewer mononuclear cells but there was no change in the small number of neutrophils. In addition the rats were hyper-sensitive to the increase in resistance to artificial respiration produced by 5-hydroxytryptamine (5-HT), given intravenously, with a shift to the left of the log dose-response curve. Lung parenchymal strips, taken from the rats on days 6, 7 and 8, were hyper-reactive to 5-HT with an increase in slope of the log dose-response curve. 3. Compounds with a wide variety of activities were evaluated for their effects on the blood eosinophilia on day 7 when given before each injection of Sephadex. The eosinophilia was reduced by glucocorticosteroids, beta-adrenoceptor agonists, aminophylline, dapsone and phenidone. 4. Dexamethasone, isoprenaline, dapsone and phenidone at doses that reduced the blood eosinophilia also reduced the changes in number of leucocytes in the BAL fluids and the hyper-responsiveness to 5-HT in vivo and in vitro, except that the effects of dapsone on the hyper-sensitivity to 5-HT in vivo did not reach significance. Aminophylline was the least effective of the drugs at reducing the blood eosinophilia and its effects on the other changes did not reach significance. Sodium cromoglycate reduced the BAL eosinophilia but had no effect on the other changes produced by Sephadex. 5. The correlation coefficients between blood eosinophil numbers and reactivity to 5-HT in vitro and sensitivity in vivo were r = 0.76, (n = 88; P < 0.001) and r = 0.53, (n = 61; P < 0.001) respectively. 6. Doses of dexamethasone, isoprenaline, dapsone and phenidone that reduced the blood eosinophilia when given before each injection of Sephadex were inactive when given up to 8 h after the Sephadex. 7. These data show an association between blood eosinophilia and hyper-responsiveness of the lung. The blood eosinophilia in the rats was triggered within the first few hours of injecting the Sephadex and drugs have been identified which inhibit this trigger.