Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from kT=5-100 keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

Mechanism of the apparent parasympathetic inhibition of adenosine induced heart rate slowing in the dog.

The inhibitory action of intravenously administered adenosine on the sinoatrial (SA) node is not expressed in the conscious dog in the presence of normal vagal tone. After pharmacological or surgical parasympathetic blockade, however, adenosine exerts a powerful negative chronotropic effect. In order to determine the reason why this action of adenosine is blocked by the intact parasympathetic nervous system, we measured the chronotropic effects of adenosine while applying a constant cholinergic stimulus to the SA node. In conscious dogs during a systemic infusion of acetylcholine at a rate sufficient by itself to inhibit the SA node, intravenous adenosine injections caused further dose dependent reductions in heart rate. In anaesthetised, vagotomised dogs, intravenous adenosine caused similar negative chronotropic effects with or without concomitant electrical stimulation of the vagus nerve. As an example, 5 mumol.kg-1 adenosine reduced heart rate by 22 (SEM 4)% from a baseline heart rate of 172(10) beats.min-1; when heart rate was lowered to 66(1) beats.min-1 by electrical vagal stimulation, this dose of adenosine reduced heart rate by 36(8)%. Propranolol had no effect on these responses. We conclude that there is no direct cholinergic inhibition of the negative chronotropic action of adenosine on the canine SA node but rather that the inhibitory action of systemically administered adenosine on the SA node is simply masked by the withdrawal of vagal tone in response to the arterial hypotension resulting from this mode of adenosine administration.

Coronary vascular resistance and myocardial oxygen consumption dynamics in response to catecholamine infusion.

These experiments were performed in order to ascertain whether activation of coronary vascular adrenergic receptors could change the time course of the coronary vasodilatation accompanying increases in myocardial metabolic activity. The left common coronary arteries of dog hearts were perfused in situ with blood at constant flow. Coronary perfusion pressure and coronary sinus blood 02 content were continuously monitored. Norepinephrine was infused into the coronary artery at 0.5 to 5 microgram.min-1. and isoprenaline at 0.5 to 2 microgram.min-1. The amplitude of the vascular resistance change was less with norepinephrine than with isoprenaline infusion for a similar change in oxygen consumption. The time course of coronary vascular resistance, after correction for the effects of vascular transit, lagged significantly behind the time course of coronary sinus 02 content in the case of norepinephrine infusion. On the average, no lag was observed with isoprenaline infusion. It is concluded that stimulation of coronary vascular adrenergic receptors can alter the time course and the magnitude of the coronary vascular response to increases in myocardial metabolic activity resulting from myocardial beta-receptor stimulation.

Insulin resistance in Cushing's syndrome.

It is well established that cortisol excess causes insulin resistance in man, but the mechanisms responsible for this insulin resistance are poorly understood. We studied five women with Cushing's syndrome with impaired oral glucose tolerance tests and seven normal subjects, plotting the shape of the insulin-induced disposal dose-response curve obtained by means of the euglycemic clamp procedure during four different plasma insulin plateaus at four infusion rates of 21, 73, 760, and 1200 mU/M2 . min. Glucose disposal (M = mg/M2 . min) was calculated as glucose amount infused to maintain euglycemia. In Cushing's syndrome the dose-response curve was shifted to the right in comparison with normal subjects, with a significantly lower M (337 +/- 35 vs. 657 +/- 76 P less than 0.01) during the highest insulin infusion rate [maximal glucose disposal (MGD)] without any significant difference in the levels of insulin half-maximally effective in the stimulation of glucose utilization. Neither erythrocyte nor monocyte maximum insulin receptor binding were different between the two populations. Four Cushing's syndrome patients were studied again after surgical treatment. A marked improvement of MGD was observed without any significant change in insulin-binding capacity. These results, particularly the marked decrease in MGD, a typical feature of postreceptor defects, indicate that cortisol-induced insulin resistance in man is due to an impairment of peripheral insulin action located beyond the hormone-receptor binding step.

The mechanism of adenosine release from hypoxic rat liver cells.

Uptake of [14C]-adenosine into freshly dispersed rat hepatocytes was inhibited 44% by dipyridamole (50 microM) and 60% by nitrobenzylthioinosine (NBTI, 20 microM). The results are consistent with the known ability of these drugs to inhibit adenosine transport in other cell types. The nucleotide analogue, alpha, beta-methylene adenosine diphosphate (AOPCP, 50 microM), inhibited by 84% the degradation of exogenous 5' AMP that occurred rapidly when this substrate alone was presented to isolated hepatocytes. This confirms the ecto-5'-nucleotidase inhibitory properties of this analogue in isolated hepatocytes. During hypoxic incubation, isolated hepatocytes released adenosine, which accumulated in the extracellular volume. Dipyridamole and NBTI each markedly attenuated this extracellular adenosine accumulation. In contrast, AOPCP had no inhibitory effect on net hypoxic adenosine release. It is concluded that hypoxic rat hepatocytes produce adenosine intracellularly and that this adenosine is released via facilitated diffusion to the extracellular space, based on the inhibition observed with the transport inhibitors. The plasma membrane enzyme ecto-5'-nucleotidase does not appear to participate in hypoxic adenosine release from these cells as indicated by the lack of effect of the nucleotidase inhibitor, AOPCP.

Mechanisms of coronary vasodilatation produced by ATP in guinea-pig isolated perfused heart.

1. Isolated hearts of guinea-pigs were perfused in vitro with a physiological salt solution via a retrograde aortic cannulation (Langendorff preparation) at constant perfusion pressure. Bolus intra-arterial injections of various vasodilator drugs were made and the coronary flow responses were measured with an electromagnetic flow probe placed in the arterial inflow circuit. Inhibitory drugs were infused intra-arterially. 2. Nitro-L-arginine (NLA; 500 microM), an NO synthesis inhibitor, decreased coronary baseline flow by 16 +/- 0.8%, converted acetylcholine-induced coronary vasodilatation to vasoconstriction and had no effect on coronary flow responses to adenosine or papaverine. Sodium nitroprusside-induced responses were enhanced during NLA infusion by 46 +/- 11%. 3. Adenosine 5'-triphosphate (ATP) increased coronary flow but coronary flow responses to ATP were not altered by infusion of NLA. 4. ATP-induced coronary dilatation was not significantly attenuated by infusion of the adenosine receptor antagonist XAC, (xanthine amine congener; 2 microM), whereas XAC decreased coronary flow responses to adenosine by 75% +/- 5%. 5. ATP-induced coronary flow responses were reduced by only 31 +/- 4% during indomethacin infusion (2.8 microM) whereas indomethacin completely eliminated the initial vasoconstriction phase and greatly attenuated the peak flow and duration of the later vasodilatation phase seen in response to arachidonic acid (0.75 nmol). Indomethacin had no effect on vasodilatations produced by adenosine or prostaglandin I2. 6. These results indicate that ATP-induced coronary dilatation in the isolated, perfused heart of the guinea-pig is not dependent upon NO production or upon degradation of ATP to adenosine. The coronary dilator action of ATP may be partially dependent (approximately 30%) upon the production of vasodilator prostaglandins.

Differential effectiveness of solar UVB subcomponents in causing cell death, oncogenic transformation and micronucleus induction in human hybrid cells.

PURPOSE: (1). To determine the biological effectiveness of two solar ultraviolet (UVB) spectra with different lower wavelength thresholds for oncogenic transformation and micronucleus induction in CGL1 cells; (2). to investigate whether the action spectra for short- and long-term effects are similar; and (3). to investigate possible links between transformation and other delayed effects. MATERIALS AND METHODS: Two spectra were derived from a solar UV simulator by using two filters: the first transmitted radiation with lambda > 284 nm, the second with lambda > 293 nm. The resulting spectra have the same UVA, but different UVB components (lambda between 284 and 320 nm, 19 W m(-2), and lambda between 293 and 320 nm, 13 W m(-2)). CGL1 cells were irradiated with 466 J m(-2) with lambda > 284 nm and 1582 J m(-2) with lambda > 293 nm. These doses were approximately equilethal. The endpoints examined were oncogenic transformation, and centromere-positive and -negative micronucleus frequencies in the directly irradiated cells and in transtheir progeny. RESULTS: At equilethal doses, the oncogenic transformation frequency in the directly irradiated cells was greater by a factor of at least 7 for lambda > 284 nm irradiation compared with lambda > 293 nm. The micronucleus induction frequency was also significantly higher with the lambda > 284 spectrum. Consistent with our previous findings, no delayed micronucleus formation was found in the progeny of cells exposed to lambda > 293 nm, while a threefold elevation above controls was seen in the progeny of cells exposed to lambda > 284 nm irradiation. This was also the case for formation of micronuclei with a centromere. CONCLUSIONS: It was found that: (1). for equilethal doses the lambda > 284 nm spectrum was more biologically effective than the lambda > 293 nm spectrum for induction of oncogenic transformation and micronucleus formation; and (2). the higher effectiveness of the lambda > 284 nm spectrum found at equilethal doses for delayed effects in the progeny of irradiated cells resembles that found for transformation. The results suggest that the UVB action spectrum for cell killing is different from that of some delayed effects, and from that of transformation.

Solar UV radiation: differential effectiveness of UVB subcomponents in causing cell death, micronucleus induction and delayed expression of heritable damage in human hybrid cells.

PURPOSE: To determine the effectiveness of two UV spectra with different UVB components for cell kill and micronucleus induction in irradiated human HeLaxskin fibroblast (CGL1) hybrid cells and their progeny. To determine the presence of reactive oxygen species (ROS) in the progeny of the irradiated cells at various post-irradiation times and their relationship with induced delayed biological effects. MATERIAL AND METHODS: A commercial solar ultraviolet simulator was used. Two different filters were employed: the first transmitted radiation with lambda>284nm and the second radiation with lambda>293nm. The resulting spectra have different UVB components (lambda between 284 and 320nm, 19 W/m(2), and between 293 and 320nm, 13 W/m(2)) and the same UVA component (lambda between 320 and 400nm, 135 W/m(2)). CGL1 cells were irradiated with various doses. Clonogenic survival and micronucleus formation were scored in the irradiated cells and their progeny. ROS were detected by incubation of cultures at various post-irradiation times with dichlorodihydrofluorescein diacetate followed by flow cytometric measurement of the final product, dichlorofluorescein. RESULTS: The biological effectiveness of the lambda>284nm spectrum was higher by a factor of 3 compared to the lambda>293nm spectrum for cell kill, and by a factor of 5 for micronucleus induction. No delayed cell death or micronucleus formation was found in the progeny of cells exposed to lambda>293nm, while a large and dose-dependent effect was found in the progeny of cells exposed to lambda>284nm for both of these endpoints. ROS levels above those in unirradiated controls were found only in the progeny of cells exposed to the lambda>284nm spectrum. CONCLUSIONS: The spectrum with lambda>284nm was more effective than that with lambda>293nm for induction of cell kill and micronucleus formation in the directly irradiated cells as well as induction of delayed effects in the progeny in the form of delayed reproductive death and micronucleus formation. The presence of ROS in the progeny of the irradiated cells may be the cause of the delayed effects.

Inactivation cross sections for mammalian cells exposed to charged particles: a phenomenological approach.

Published data on inactivation of V79 cells irradiated with monoenergetic proton and ion beams (He, C, O, Ne) have been analysed. Values for RBE alpha, RBE10% and the inactivation cross section sigma have been evaluated in the LET range between 5 and 400 keV.micron-1. RBE against LET curves and inactivation cross sections against LET and against Z*2/beta 2 curves have been studied in a comparative approach with respect to the different ion types. RBE-LET curves depend strongly on the type of ion for LET > 30 keV.micron-1. At LET < 30 keV.micron-1 and low doses protons show the greatest effectiveness; at LET > 30 keV.micron-1 and high doses He ions provide the most effective radiation. Apart from protons, separation among the various ion curves is less marked in the sigma against Z*2/beta 2 plot than in the sigma against LET plot. sigma against Z*2/beta 2 curves for ions with 2 < or = Z < or = 10 and 200 < Z*2/beta 2 < 1500 show a common trend independent of Z and are well represented by a linear relationship.

Investigating incorporation and distribution of radionuclides in trinitite.

Most of the surface explosions in nuclear tests have released radioactivity to the environment in the form of bulk glassy materials originating from the melting of sandy soil in the neighbourhood of ground zero. In view of clarifying issues concerning the mechanism of formation and the radiological impact of these materials, we investigated incorporation and volume distribution of radionuclides in a typical fragment of trinitite, the glassy substance generated following the first nuclear test (Trinity Site, New Mexico, 1945). Specific activities were determined by γ-spectrometry for the most significant fission and activation products. In particular, (152)Eu activity was used to estimate the original point of collection of the sample with respect to ground zero. After embedding in an epoxy resin, the sample was then sliced to perform cross-sectional ß- and α-autoradiograph. α-spectrometry was also carried out on a fine powder obtained by surface abrasion. In the ß-autoradiography, hot spots were distinguishable in the proximity of the blast side, over a 1000 times less intense background of sand activation products. Also α-contamination (from (239+240)Pu and (241)Am) was mostly concentrated within the superficial layer, in a fraction of only 20% of the overall volume of the sample, exhibiting a discontinuous, droplet-like distribution. This evidence would partially support a recent hypothesis on trinitite formation according to which most of the glass layer was formed not on the ground but by a rain of material injected into the fireball that melted, fell back, and collected on a bed of already fused sand.

Refresher course for teaching cardiovascular physiology.

This report presents highlights of a refresher course presented at Experimental Biology '99 on Saturday, April 17, 1999, in Washington, District of Columbia.

Teaching the principles of hemodynamics.

Knowledge of hemodynamic principles is crucial to an understanding of cardiovascular physiology. This topic can be effectively taught by discussing simple physical principles and basic algebraic equations. A variety of examples from everyday observations can be used to illustrate the physical principles underlying the flow of blood through the circulation, thereby giving the student an experiential feel for the topic in addition to an understanding of theory. Moreover, opportunities abound for showing how each hemodynamic principle can explain one or another functional feature of the cardiovascular system or a cardiovascular pathophysiological state. Thus hemodynamics can be used as an organizational thread to tie together other aspects of cardiovascular physiology.

Glibenclamide attenuates adenosine-induced bradycardia and coronary vasodilatation.

The effects of the ATP-sensitive K(+)-channel blocker glibenclamide on the cardiovascular responses to adenosine in dogs were determined. Adenosine (0.01-20 mumol/kg iv) caused coronary vasodilatation, arterial hypotension, and bradycardia in dogs with either combined beta-adrenergic and muscarinic receptor blockade or with bilateral cervical vagotomy plus beta-adrenergic receptor blockade. The 50% effective dose for adenosine-induced coronary dilatation was increased from 0.13 +/- 0.04 mumol/kg in the control state to 1.1 +/- 0.5 mumol/kg after 2 mg/kg of glibenclamide (P less than 0.001). Adenosine at 5 mumol/kg reduced heart rate by 19 +/- 5% from a baseline of 158 +/- 6 beats/min in five anesthetized dogs. After glibenclamide (10 mg/kg), this dose of adenosine failed to cause a significant change in heart rate. The arterial hypotensive effects of adenosine were also attenuated by glibenclamide. Thus glibenclamide inhibited adenosine-induced bradycardia, hypotension, and coronary dilatation. On the other hand, glibenclamide did not affect the reductions in heart rate caused by vagus nerve stimulation. The mechanism of this adenosine antagonism is not known but, in the case of bradycardia, it does not appear to involve any of the steps shared in common by both adenosine-induced and vagal responses of the sinoatrial node.

Dynamics of myocardial oxygen consumption and coronary vascular resistance.

Coronary vascular resistance may be regulated in part by substances whose concentrations are determined by or reflect the rate of myocardial oxygen consumption (e.g., adenosine, vessel wall PO2). We tested this hypothesis by comparing the time course of changes in myocardial oxygen consumption and coronary vascular resistance following 20 beat/min changes in heart rate. Main left coronary arteries of in situ dog hearts were perfused with blood at constant flow. Coronary sinus O2 content was monitored continuously with a densitometer and reflected the time course of changes in oxygen consumption and also the effects of vascular transit between tissue and the coronary sinus. These transit effects were estimated from dye transit curves and added to the time course of changes in coronary perfusion pressure which was proportional to coronary vascular resistance at constant flow. Coronary sinus O2 content changes preceded the adjusted time course of vascular resistance. This supports the hypothesis that coronary vascular resistance is regulated in part by factors closely linked to oxidative metabolism.

Superoxide anion selectively attenuates catecholamine-induced contractile tension in isolated rabbit aorta.

Xanthine oxidase-derived oxygen metabolites caused a selective loss of norepinephrine-induced contractile tension in rings and helical strips from rabbit aorta. Phenylephrine-induced tension was not affected. The relaxation was selectively and completely blocked by superoxide dismutase but not by catalase. Isoproterenol-induced relaxation was also reversed by xanthine oxidase-derived oxygen metabolites. These observations are consistent with the chemical reaction of superoxide anion with catecholamines and suggest that the reaction may have significance at physiological concentrations of norepinephrine. The time course of the effects of superoxide generation on contractile tension was consistent with the properties of the chemical reaction (measured spectrophotometrically) and with the dependence of tone on norepinephrine concentration. These results indicate that superoxide anion, in situations at which submicromolar concentrations of this reduced oxygen metabolite are present, will selectively oxidize catecholamines, which may attenuate local adrenergic regulation.

Role of nitric oxide in hypoxic coronary vasodilatation in isolated perfused guinea pig heart.

To test the hypothesis that nitric oxide (NO) mediates hypoxic coronary dilatation in situ, isolated guinea pig hearts were perfused at constant pressure (Langendorff technique) with physiological salt solution. Switching from a control perfusate (95% O2-5% CO2) to one equilibrated with a lower O2 tension (20% O2) induced a large, but submaximal and reproducible, coronary dilatation. The NO synthase inhibitor NG-nitro-L-arginine (L-NNA) diminished baseline flow (3.67 +/- 0.24 vs. control 5.11 +/- 0.42 ml.min-1 x g-1; P < 0.05) and selectively blocked the coronary flow response to acetylcholine without reducing the response to papaverine. L-NNA reduced the absolute increase in coronary flow during hypoxia by 27 +/- 2% (delta flow = 5.83 +/- 0.49 vs. control delta flow = 8.04 +/- 0.74 ml.min-1 x g-1; P < 0.05). Hypoxic coronary dilatation was unaffected by infusion of the thromboxane mimetic U-46619, which decreased baseline coronary flow to the same extent as L-NNA. Prior addition of indomethacin did not alter the attenuating effect of L-NNA. Hypoxic coronary dilatation during constant flow perfusion at 14.7 +/- 0.28 ml/min was reduced by 65 +/- 5% after L-NNA. Therefore, the NO component of the response was not a consequence of the reduced baseline flow observed in the presence of L-NNA, did not depend on prostaglandin synthesis, and was not secondary to increased flow or intravascular shear stress. We conclude that hypoxic coronary vasodilatation in isolated guinea pig hearts is partially mediated by NO.

Adenosine causes bradycardia in pacing-induced cardiac failure.

BACKGROUND: In normal, conscious dogs, systemic injection of adenosine causes arterial hypotension and a baroreceptor reflex tachycardia mediated in part by withdrawal of vagal tone from the sinoatrial node. After vagal section or muscarinic receptor blockade, however, adenosine injection causes bradycardia via a direct sinoatrial node inhibition. Because cardiac failure is marked by a loss of vagal tone, we hypothesized that adenosine injection in dogs with failing hearts would reduce heart rate. METHODS AND RESULTS: Mongrel dogs were instrumented with indwelling catheters, manometers, and ventricular pacing electrodes. After the dogs had recovered from the surgery, the ventricles were paced continuously at 210 beats per minute for 3 weeks, followed by pacing at 240 beats per minute for an additional week. This regimen caused mild ventricular and more striking atrial hypertrophy and a gradual onset of physiological and clinical signs of congestive heart failure. Adenosine injections that caused large tachycardias before the pacing regimen began caused progressively smaller increments in heart rate during the first 2 weeks of pacing. After 3 and 4 weeks, adenosine injections caused overt reductions in heart rate despite the concomitant arterial depressor response. CONCLUSIONS: We conclude that the loss of vagal tone associated with the development of cardiac failure unmasks the direct negative chronotropic effect of exogenous adenosine on the sinoatrial node.

Effects of alkylxanthines and calcium antagonists on adenosine uptake by cultured rabbit coronary microvascular endothelium.

Adenosine uptake by cultured rabbit coronary microvascular endothelial cells was studied. Radiolabeled [2-3H]-adenosine, present initially in the extracellular space at 10(-6) mol/l, was incorporated into the cell cultures at a steady rate during 30 s-3 h incubations. Incorporated 3H was found mostly (83%) in adenine nucleotides. Incorporation of [3H]-adenosine was attenuated by an adenosine deaminase inhibitor (EHNA) but only at adenosine concentrations of 10(-5) mol/l or higher. Adenosine transport inhibitors (dipyridamole, nitrobenzylthioinosine) attenuated 3H incorporation. Adenosine uptake was also diminished by certain structural analogues of adenosine (e.g., 2-chloroadenosine), by several alkylxanthine drugs (theophylline, isobutylmethylxanthine, enprofylline and 8-phenyltheophylline), and by certain calcium antagonists (verapamil, nifedipine and trifluoperazine). The mechanisms of actions of these agents on adenosine uptake do not appear to be related to phosphodiesterase inhibition, adenosine receptor antagonism or calcium antagonism. The effects of varying adenosine metabolism may contribute to the pharmacologic actions of these agents.