Effect of atenolol on contractile function Essays

Effect of atenolol on contractile function Essays Effect of atenolol on contractile function Essay Effect of atenolol on contractile function Essay Consequence of Tenormin on contractile map during ischaemia and reperfusion in the rat isolated perfused bosom Purpose:?-blockers are thought to exercise good effects on the ischaemic bosom. We examine the consequence of Tenormin, a selective ?1 adversary, on contractile map at low ( 10 µM ) and high ( 50 µM ) concentrations in the stray rat Black Marias. Methods:Isolated rat Black Marias ( n=8 in each group ) were perfused with Krebs solution for 5-min. They were so perfused with test solution: controls incorporating Krebs, or selective Tenormin ( 10 µM ) or high concentration of Tenormin ( 50 µM ) . After 10-min, the Black Marias were subjected to 30-min of planetary ischaemia ( zero-flow ) followed by reperfusion with the same trial solution as earlier. The starling curves were constructed prior to and after ischemia. Consequences:No important alterations in maximal ischemic contracture and clip to half maximum contracture were seen in Black Marias pre-treated with test solutions. LVEDP was increased by 4-fold in control for Tenormin ( 10 µM ) and by 12-fold in Black Marias treated with control for Tenormin ( 50 µM ) , 5-min after reperfusion, comparing to pre-ischemic values ( P lt ; 0.05 for control for atenolol 10 µM vs. control for atenolol 50 µM ) . No alterations in coronary flow or bosom rate were observed between groups at baseline and during reperfusion. LVEDP was quickly increased from 2.6 ±1.3 mmHg to 28.6 ±9.0 mmHg in control for Tenormin ( 50 µM ) and from 4.0 ±1.6 mmHg to 27.3 ±7.6 mmHg with Tenormin ( 50 µM ) , in the starling curves constructed with 60 µl of increase in the balloon, prior to the ischemia and after reperfusion ( P lt ; 0.05 for pre-ischaemic perfusion vs. post-ischaemic reperfusion ) . Decisions:The present survey shows that Tenormin has no cardioprotective effects on contractile map during ischemia and reperfusion in stray rat Black Marias. Introduction ?-blockers have been widely shown to hold cardioprotective effects on ischaemia and hypoxic Black Marias, including betterment in ventricular map, and ensuing in a reduced mortality rate in ischaemic bosom disease patients ( Wallace et al. , 1998 ) . Although, the exact mechanisms by which cardioprotective agents act are non yet to the full understood, ? blockers are thought to exercise good effects on the ischaemic bosom by take downing myocardial O ingestion as a effect of decreased contractility and bosom rate ( HR ) . The consequence of ?-adrenergic receptor adversary, Tenormin, on the contractile map in the stray bosom is still a controversial subject of research. Several surveies have shown that Tenormin does non protect against ischaemia-reperfusion in a theoretical account of an stray perfused bosom exposed to planetary or no-flow ischemia ( Singh et al. , 1995 ; Harada et al. , 1981 ) . However, on the other terminal of the spectrum there have been studies bespeaking that an ischemic period of longer than 3-4 min induces important release ( 2700pmol/g bosom ) of endogenous catelchoamines ( norepinephrine ) in the stray rate bosom ( Wollenberger and Shabab, 1965 ) . In add-on, an flood of catecholamines during the reperfusion period has besides been reported, which is thought to be a consequence of washout of norepinephrine antecedently released from the sympathetic nervousnesss or due to a reperfsion activated release ( SchSmig et al. , 1984 ; Carlsson et Al 1985 ) . It is suggested that cate cholamines mediates contractility of the cardiac musculus. These agents work by triping ?-adrenergic receptors, taking to the activation of adenylyl cyclase, which so elevates the degrees of a secondary courier camp. Increased camp activates protein kinase A ( PKA ) , which causes increased entry of Ca into the cell, ensuing in positive inotropy ( increased contractility ) in the cardiac musculus. The positive inotropic consequence due to high degrees of endogenous catecholamine should be hence attenuated by the usage of selective concentration of ?1-adrenoceptor adversary, Tenormin. In order to prove the counter consequence of Tenormin, we use a selective concentration of Tenormin ( 10 µM ) on a normal operation rat bosom and in a theoretical account in of 30-min of globally ischemic induced rat bosom followed by 10-min of reperfusion. Since the release of endogenous catecholamines upon ischaemia is controversial, we besides used a high concentration of Tenormin ( 50 µM ) to find counter action of non-selective atenolol dose on receptors other than ?1-adrenoceptors, and to see if it enhances recovery in contractile map upon ischemia. The Langendorff scenes were used in this experiment as it is a widely used readying which provides valuable information on left ventricular systolic and diastolic force per unit areas and their derived functions in Black Marias, subjected to ischemia ( Skrzypiec-Spring et al. , 2007 ) Methods Anaesthesia, bosom deletion and perfusion All experiments were carried out in understanding with the United Kingdom Home Office Guide on the Operation of the Animals ( Scientific Procedures ) Act 1986. Rats ( male Wistar strain ; Sigma chemicals U.K. , 230-280g ; n=8 in each group ) were anaesthetised with Nembutal by an intraperitoneal injection ( 60mg/kg ) . An endovenous injection of Lipo-Hepin ( 300 I.U ) , an decoagulant, was given to forestall the formation of thrombi. Heartss were so excised: foremost, the stop was accessed by a transabdominal scratch and cut carefully to expose the thoracic pit. The thorax was opened by a bilateral scratch along the lower border of the last to first ribs and the pectoral coop was so reflected over the animate being s caput, thereby exposing the bosom. The bosom was so cupped between the fingers ( in order to avoid bruise hurt ) and lifted somewhat before incising the aorta, vena cava and pneumonic vass. To avoid any ischaemic hurt, after deletion, Black Marias were instantly immersed in ice-cold perfusion solution ( 4 °C ) incorporating following composing ( in millimeter ) : NaClA 118.5, NaHCO3 25.0, KCl 3.0, MgSO4 1.2, NaH2PO4 1.2, gluc ose 11.1, CaCl2 1.4, followed by the canulation of the aorta and the bosom was so perfused retrogradely down the aorta, harmonizing to the Langendorff manner ( 1895 ) with a changeless hydrostatic force per unit area equivalent to 100 cmH2O, and perfusion solutions aerated with a gas mixture of 95 % O2 + 5 % CO2, delivered at pH of 7.4 at 37 °C. A changeless temperature 37 °C of the perfusate was maintained with a heat money changer ( Techne Circulators C85-A, UK ) . Perfusion solutions were non recirculated. Measurement of left ventricular force per unit area utilizing intraventricular balloons After remotion of the left atrial extremity, a fluid-filled compliant balloon was attached via a blunt-ended acerate leaf ( 21 gage ) and a catheter to a force per unit area transducer, which was carefully inserted into the left ventricular pit via the mitral valve. The balloon was used to find the contractile activity of the bosom: the measuring of left ventricular systolic ( LVEDP ) and diastolic force per unit areas and ( by difference ) left ventricular developed force per unit area ( LVDP ) and the bosom rate. The balloon was ab initio inflated with H2O from a microsyringe until a developed force per unit area of 100 mmHg was obtained so farther volume was added to bring forth starling curve. The force per unit area transducer was connected to a biological recording system equipped with amplifier ( PowerLab 4/25, AD Instruments ) . Experimental protocol The stableness and duplicability of each readying was monitored by mensurating the baseline contractile map during the first 15-min of aerophilic perfusion. Heartss were perfused for an initial 5-min with a standard Krebs solution, followed by another 10-min perfusion with one of the several trial solutions, which were perfusion solutions incorporating Tenormin ( 10 µM ) , control for Tenormin ( 10 µM ) , atenolol ( 50 µM ) and control for Tenormin ( 50 µM ) . Standard Krebs solution was switched to one of the trial solution in a randomized blinded mode, in order to avoid prejudice. Blinding was achieved by coding the solutions, with the codification unknown to the person. Ethanol ( 0.05 % v/v ) was moving as a drug vehicle for Krebs solution, and added to all the perfusion solutions to extinguish vehicle as a beginning of discrepancy. The relationship between the intraventricular volume and the force per unit area was studied as described by Otto Frank in 1895, the Frank-Starling jurisprudence of the bosom ( Frank et al. , 1895 ) . The balloon was deflated to the nothing volume, prior to the building of starling curves, and so increasingly inflated by adding 0.02ml increases to the balloon ( 30s at each increase ) , until a diastolic force per unit area of 20 mmHg could be observed, during which clip systolic, diastolic, and developed force per unit area, bosom rate and coronary flow were monitored. The balloon was deflated back to zero volume. After baseline experiments, the Black Marias were made globally ischemic ( zero-flow ischemia ) for 30-min by clamping off the aortal flow. During ischemia, Black Marias were immersed in Krebs solution and temperature was recorded with a thermometer. Heartss were so reperfused for 10-min under the same conditions of baseline ; therefore the intraventricular balloon was deflated sufficiently to re-establish a developed force per unit area of 100 mmHg. Another starling curve was so constructed via the same intraventricular balloon method and the appropriate measurings were recorded. Measurement of coronary flow The measuring of coronary flow was performed by mensurating timed volumes of perfusate run outing out of the right atrium. Flow was calculated as ml/min/g of wet tissue, therefore taking into history any differences in weight between single Black Marias. Drugs All the drugs were obtained from Sigma Chemical Co. ( Dorset, UK ) . Atenolol was diluted in Krebs solution, in order to accomplish appropriate concentrations ( 10 µM and 50 µM ) . Statisticss Datas are expressed as mean ±SEM. Two-tailed t-test was performed presuming two-sample equal discrepancy ( homoscedastic ) . A difference was considered to be statistically important when P lt ; 0.05. Consequences Development of ischaemic contracture during 30 min of planetary Ischemia Maximal ischemic contracture was determined by mensurating the maximal rise in diastolic force per unit area from the baseline point. Time to onset 50 % of the maximum contracture was besides found, which is an accurate step to measure ischemia-induced diastolic disfunction ( Fig.1 ) . Conventional representation of development of ischemic contracture ( during 30 min of planetary ischemia ) for an single hint of Tenormin ( 10 µM ) in the rat isolated bosom. A rapid rise in LVEDP was noticed shortly after the initiation of planetary ischemia. Owing to the fact that volume in the balloon was kept changeless therefore any addition in LVEDP was stand foring contracture of the stray rat bosom. Function during the ischemia was non the Centre of attending here and merely certain effects of the intercessions were noted. There were no important differences, in footings of the maximum contracture and clip to achieve 50 % of maximal contracture, between the two control groups and the comparative values of Tenormin ( 10 µM ) and Tenormin ( 50 µM ) group ( Fig.2 ) . The clip to half-maximal contracture was 20.8 ±4.3 min with a peak contracture of 30.8 ±6.1 mmHg in the Black Marias treated with control for Tenormin ( 10 µM ) . No important consequence of planetary ischaemic on contracture development was seen in Black Marias treated with Tenormin ( 10 µM ) i.e. , the clip to half maximal contracture occurred at 16.0 ±2.7 min and peak contracture at 38 ±7.2 mmHg. This was besides the instance for Black Marias perfused with high concentration of Tenormin ( 50 µM ) , ensuing in peak contracture of 41.3 ±4.5 mmHg and the clip to half maximum contracture of 14.4 ±2.2 min, in comparing to the matching values of control for high concentration in which peak contracture and half-maximal contracture were delayed to 43.0 ±7.6 mmHg and 15.8 ±2.4 min, severally. Consequence of Tenormin ( 10 µM ) and Tenormin ( 50 µM ) on extremum ischaemic contracture development and clip to half-maximal ischemic contracture. Datas are mean ±S.E.M. There were no important differences between groups. n=8 in each group. Postischaemic profile for: ( a ) terminal diastolic force per unit area, ( B ) developed force per unit area, ( degree Celsius ) bosom rate and ( vitamin D ) coronary flow in stray rate Black Marias treated with Tenormin ( 10 µM ) , control for Tenormin ( 10 µM ) , atenolol ( 50 µM ) and control for Tenormin ( 50 µM ) . Baseline represents values taken 1-min anterior to the ischemia ; 5 and 9 min represents reperfusion clip points after 30-min of planetary ischemia. Valuess are average  ± SEM ; n=8 in each group. *P lt ; 0.05 ( control for atenolol 10 µM vs. control for atenolol 50 µM ) . Postischaemic recovery of terminal diastolic force per unit area, developed force per unit area, bosom rate and coronary flow LVEDP rose by 4-fold in control for Tenormin ( 10 µM ) 5-min after reperfusion comparing with the values before the oncoming of ischemia ( Fig.2 ) . In contrast, a rapid addition by 12-folds was noticed in Black Marias treated with control for Tenormin ( 50 µM ) ( P lt ; 0.05 control for atenolol 10 µM vs. control for atenolol 50 µM ) . LVDP fell down by 21 % and 57 % in Black Marias treated with controls for Tenormin ( 10 µM and 50 µM, severally ) 5-min after the oncoming of reperfusion comparing with the values before the oncoming of ischemia. This clearly shows that post-ischaemic recovery of LVDP was hapless in Black Marias treated with control solutions. The corresponding decrease in LVDP by a little border of 4 % and 13 % in Black Marias treated Tenormin ( 10 µM ) and Tenormin ( 50 µM ) severally, may be a small surprising but such values are non extremely important in comparing to the controls, hence no important betterment in post-ischaemic LVDP recovery is observed. No important alterations in coronary flow were seen between groups at baseline. During reperfusion, no damage in the coronary flow was apparent in the Black Marias treated with Tenormin ( 10 µM ) and high Tenormin ( 50 µM ) in comparing to the comparative values for control groups. Besides, no important difference in the bosom rate was found at the baseline and at the terminal of 10-min reperfusion between any of the groups. With 60 µM of increase in the balloon, there was a significant rise in the diastolic force per unit area for the starling curve taken prior to the oncoming of ischemic in comparing with values taken 30-min after the ischemia, for Black Marias treated with Tenormin ( 50 µM ) , and control for Tenormin ( 50 µM ) . The diastolic force per unit area drastically increased from 2.6 ±1.3 mmHg to 28.6 ±9.0 mmHg ( P lt ; 0.05 ) for Black Marias treated with control for Tenormin ( 50 µM ) and a corresponding rise from 4.0 ±1.6 mmHg to 27.3 ±7.6 mmHg ( P lt ; 0.05 ) in Tenormin ( 50 µM ) treated Black Marias. This clearly indicates a presence of diastolic disfunction. No important rise in diastolic force per unit area was seen in Black Marias treated with control for Tenormin ( 10 µM ) and Tenormin ( 10 µM ) . Relationship between diastolic force per unit areas obtained with 60 µM of increase in the balloon prior to the oncoming of 30 min ischemic and postischaemia in the rat isolated bosom treated perused with the trial solutions. Datas are mean ±S.E.M. ( *P lt ; 0.05 pre-ischaemic perfusion vs. post-ischaemic reperfusion ) . n=8 in each group. Developed force per unit area dropped down by 21 % and 28 % in Black Marias treated with Tenormin ( 10 µM ) and Tenormin ( 50 µM ) , severally, for the values taken before the oncoming of ischemia and after 30 min of ishaemic period with 60 µM of increase in the balloon. In contrast, a little rise in developed force per unit area by 9 % and 24 % in Black Marias treated with control for Tenormin ( 10 µM ) and control for Tenormin ( 50 µM ) . In both instances, an addition or lessening in developed force per unit area was non extremely important. Discussions A rise in ischaemic contracture was noticed in the current survey, which is thought to be due to depletion of ATP production via glycolytic tract ( anaerobiotic glycolysis ) instead than entire cellular ATP content ( Kingsley et al. , 1991 ) . It is besides believed that an early contracture may hold Ca constituent as intracellular free Ca ions are reported as a cardinal go-between of ischemic hurt ( Tani M. , 1990 ) . In order to understate ischaemic hurt we used a recommended concentration of Ca ( 1.4mmol/L ) in the perfused solutions ( Fiona et al. , 2003 ) . No decrease in the maximal-ischemic contracture was seen in Black Marias pre-treated with atenolol therefore Tenormin did non hold any contraceptive consequence on ischemic contracture development. This was farther apparent by no protraction of the clip to half maximum contracture, in the presence of Tenormin, proposing that ischaemic hurt was non reversed in this instance. An expected ague rise in ventricular diastolic force per unit area and a diminution in developed force per unit area was detected in all ischemic-subjected Black Marias ( Porter T. , 1895 ) . Atenolol did non do important postischaemic recovery in LVPD and LVEDP during reperfusion. Although, Black Marias treated with control for Tenormin ( 50 µM ) had a rapid rise in LVEDP in comparing to the Black Marias treated with control for Tenormin ( 10 µM ) such difference could be due to variableness in the consequences as experiment was carried out in two different yearss and environmental conditions may hold influenced consequences to a certain extent. In add-on, the dependability of consequences is besides questionable as few values could non be taken during the experiments due to an oncoming of ventricular fibrillation taking to inaccurate average values. No major alterations in bosom rate and coronary flow were seen between groups at baseline and 10 min after reperfusion in Black Marias subjected to ischaemia. Changes in coronary flow are usually accompanied by alterations in LVDP ; hence no important alterations in coronary flow confirm the cogency of LVDP step as antecedently described. There was a mark of diastolic disfunction as evident in the starling curve constructed prior to the oncoming of ischemic in comparing to the values taken after reperfusion. This diastolic disfunction further indicates no mediated cardioprotective effects of Tenormin as preconditioning, and reperfusion with Tenormin did non rarefy contractile disfunction. In drumhead the present survey shows that both low ( 10 µM ) and high ( 50 µM ) doses of Tenormin did non hold any cardioprotective effects on ischaemic/reperfusion hurt in stray rat Black Marias. The effectivity of ?-adrenoceptor encirclement in the ischaemic reperfused stray Black Marias has been demonstrated in the past surveies. Lu et al reported that pretreatment with Tenormin did non demo betterment in postischemic recovery in the stray coney Black Marias ( Lu et al. , 1990 ) . They used 10 mg/l of Tenormin in the Black Marias subjected to 25-min ischemia, followed by 30 min of reperfusion. The average functional recovery of aortal flow was merely 6 % in Black Marias treated with a control solution and no important rise in aortal flow recovery could be observed with Tenormin treated Black Marias. In the bosom, ?-adrenergic responses to catecholamines are most normally associated with the activation of ?1-adrenergic receptors. Nevertheless, cardiac musculus besides possesses a important population of ?2-adrenergic receptors ( Brodde. , 1991 ; Kaumann et al. , 1987 ) and a infinitesimal population of a1-adrenoceptors ( Lutz et al. , 2003 ) . In this survey, we used a selective concentration of Tenormin, which has antecedently shown to hinder the positive ionotrophic consequence of catecholamines. The selective concentration of the Tenormin ( 10 µM ) was chosen to be 1  ± 2 orders of magnitude above its several pA2 ( Borje J. , 1979 ; Kenakin. , 1993 ) . No consequence of selective Tenormin on cardiac recovery was seen, which could be due to two grounds: a ) there was no endogenous release of catecholamine B ) an increased contractility was a consequence of catecholamine moving on receptors other than ?1-adrenoceptors ( ?2 and a1 receptors ) , which are non antagonised by selective concentration of Tenormin. If latter was the instance, should we have observed a recovery in contractile map with higher concentration of Tenormin? Well, no discernible recovery in cardiac map was seen with higher doses of Tenormin ( 50 µM ) . For case, if atenolol ( 50 µM ) was moving on ?2-adrenoreceptors so it would hold caused a diminution in bosom rate, which was non the instance in this survey. It could besides intend that 5-fold higher concentration of Tenormin ( 50 µM ) . used in this survey, was non powerful plenty to move on receptors other than ?1-adrenoceptors ( ?2 or a1 receptors ) . On the footing of our consequences, we conclude that Tenormin did non hold a cardioprotective consequence, which could be due to really low concentration of catecholamines present in the nervus terminations. However, the dependability of our decision is so problematic as there was a batch of variableness in the consequences which made it complicated to construe. Study restrictions Perfusion force per unit area was provided by adding appropriate sum of trial solution to the reservoir. In some instances, reservoir was non topped up and this would hold led to low hydrostatic force per unit area, therefore a low coronary flow the latter is thought to be straight relative to perfusion force per unit area ( Fiona et al. , 2003 ) . It is hence of import to utilize a changeless perfusion force per unit area of 60-100 mmHg utilizing a perfusion force per unit area transducer, connected to a tripartite pat instantly above the aortal cannula ( Fiona et al. , 1999 ) . In this survey we merely controlled temperature of perfusion solution utilizing a heat money changer. Surveies have shown that alterations in tissue temperature are associated with LVDP and bosom rate steps ( Fiona et al. , 2003 ) . A alteration could be made by environing the bosom with a thermostatically controlled water-jacked chamber to keep its temperature at 37.0 ±0.2 °C throughout the experiment. In add-on, Black Marias could besides be maintained at 37 °C during ischaemic period. For better reading of consequences, one could utilize another ?-adrenoceptor adversary, such as propranolol, which acts on both ?1 and ?2-adrenoceptors. This would bespeak drug action on ?2-adrenoceptors, therefore giving us a clearer image of the presence of catecholamines, if any. On the other manus, catecholamine could be added exogenously, in the presence or absence of Tenormin, to detect any differential effects. Other possible betterments include widening the reperfusion clip from 10-min to 1hr, in order to detect farther alterations in cardiac map. Furthermore, the whole experiment could be done in one twenty-four hours clip to minimise influences of environmental conditions. Mentions: 1. Brodde, O.-E. ?1- and ?2-Adrenoceptors in the human bosom: belongingss, map, and changes in chronic bosom failure. Pharmacol. Rev. 43: 203-242, 1991 2. Frank O. Zur Dynamik des Herzmuskels.Z Biol32: 370-437, 1895. 3. Harada S, Ban T, Fujita T, Koshiro A. Negative inotropic effects and the hydrophobicity of beta-adrenergic barricading agents. Arch Int Pharmacodyn 1981 ; 252:262-71. 4. Hein A ; Schmitt, 2003. L. Hein and J.P. Schmitt, a1-Adrenoceptors in the bosom: friend or foe? . J Mol Cell Cardiol 35 ( 2003 ) , pp. 1183-1185. 5. Johansson B. Effectss of Tenormin, metroprolol, and pamatolol on cardiac and vascular ?-adrenoceptorsA in the rat.J Cardiovasc Pharmacol 1979 ; 1:287-98 6. Kaumann, A. J. , and H. Lemoine. ?2-adrenoceptor-mediated positive inotropic consequence of epinephrine in human ventricular myocardium. Quantitative disagreements with binding and adenylate cyclase stimulation. Naunyn Schmiedebergs Arch. Pharmacol. 335: 403-411, 1987 7. KENAKIN, T. ( 1993 ) . Pharmacological Analysis of Drug-Receptor Interaction. pp. 376- 378. New York: Raven Imperativeness 8. Kingsley PB, Sako EY, Yang MQ, Zimmer SD, Ugurbil K, Foker JE, From AH. Ischemic contracture begins when anaerobiotic glycolysis Michigans: a 31P-NMR survey of stray rat Black Marias. Am J Physiol. 1991 ; 261: H469-H478. 9. L. Carlsson, T. Abrahamsson and O. Almgren, Local release of myocardial noradrenaline during acute-ischemia an experimental-study in the stray perfused rat-heart, J. Cardiovasc. Pharm. 7 ( 1985 ) , pp. 791-798. 10. Lu HR, Vandeplassche G, Wouters L, Flameng W, Borgers M. Effects of /3-adrenoceptor adversaries on cardiac map in ischemic-reperfused myocardium of the stray on the job coney bosom. Eur J Pharmacol. 1990 ; 184:65-74. 11. Porter T. On the consequences of ligation of the coronary arterias. J Physiol ( London ) 1895 ; 15:121. 12. Schomig A, Dart AM, Dietz R, Mayer E, KObler W. Release of endogenous catecholamines in the ischaemic myocardium of the rat. Separate A: Locally mediated release. Circ Res 1984 ; 55: 689-701. 13. Singh N, Seneviratne CK, Singal PK. Propranolol protection against ischaemic hurt is accompanied by addition in antioxidant activities without any alteration in messenger RNA. FASEB J 9 ( 1995 ) 14. Skrzypiec-Spring M, Grotthus B, Szelag A, Schulz R, Isolated bosom perfusion harmonizing to Langendorff still feasible in the new millenary, J. Pharmacol. Toxicol. Methods 55 ( 2007 ) , pp. 113-126. 15. Sutherland FJ, Hearse DJ. The stray blood and perfusion fluid perfused bosom. Pharmacol Res 2000 ; 41:613-27. 16. Sutherland, F. , Shattock, M. , Baker, K. , and Hearse, D. 2003a. Mouse isolated perfused bosom: features and cautiousnesss. Clin. Exp. Pharmacol. Physiol. 30: 867-878. 17. Tani M. Mechanisms of Ca2+ overload in reperfused ischaemic myocardium. Annu Rev Physiol 1990 ; 52: 543-59. 18. Wallace A, Layug B, Tateo I, et Al. Contraceptive Tenormin reduces postoperative myocardial ischaemia. McSPI Research Group. Anesthesiology 1998 ; 88: 7-17. 19. Wollenberger and Shabab, 1965. A Wollenberger and L Shabab, Anoxia-induced releases of norepinephrine from isolated perfused bosom. Nature 207 ( 1965 ) , pp. 88-89.