Apelin-induced cardioprotection against ischaemia/reperfusion injury: roles of epidermal growth factor and Src.

AIM: Apelin, the ligand of the G-protein-coupled receptor (GPCR) APJ, exerts a post-conditioning-like protection against ischaemia/reperfusion injury through activation of PI3K-Akt-NO signalling. The pathway connecting APJ to PI3K is still unknown. As other GPCR ligands act through transactivation of epidermal growth factor receptor (EGFR) via a matrix metalloproteinase (MMP) or Src kinase, we investigated whether EGFR transactivation is involved in the following three features of apelin-induced cardioprotection: limitation of infarct size, suppression of contracture and improvement of post-ischaemic contractile recovery. METHOD: Isolated rat hearts underwent 30 min of global ischaemia and 2 h of reperfusion. Apelin (0.5 µm) was infused during the first 20 min of reperfusion. EGFR, MMP or Src was inhibited to study the pathway connecting APJ to PI3K. Key components of RISK pathway, namely PI3K, guanylyl cyclase or mitochondrial K+ -ATP channels, were also inhibited. Apelin-induced EGFR and phosphatase and tensing homolog (PTEN) phosphorylation were assessed. Left ventricular pressure and infarct size were measured. RESULTS: Apelin-induced reductions in infarct size and myocardial contracture were prevented by the inhibition of EGFR, Src, MMP or RISK pathway. The involvement of EGFR was confirmed by its phosphorylation. However, neither direct EGFR nor MMP inhibition affected apelin-induced improvement of early post-ischaemic contractile recovery, which was suppressed by Src and RISK inhibitors only. Apelin also increased PTEN phosphorylation, which was removed by Src inhibition. CONCLUSION: While EGFR and MMP limit infarct size and contracture, Src or RISK pathway inhibition suppresses the three features of cardioprotection. Src does not only transactivate EGFR, but also inhibits PTEN by phosphorylation thus playing a crucial role in apelin-induced cardioprotection.

Injured cardiomyocytes promote dental pulp mesenchymal stem cell homing.

BACKGROUND: The heart is unable to regenerate its tissues after severe injuries. Stem cell therapy appears to be one of the most promising approaches, though preclinical results are hitherto contradictory and clinical trials scanty and/or limited to phase-I. The limited knowledge about stem cell early homing in infarcted cardiac tissues can concur to this scenario. METHODS: The stem cell migration was assessed in in-vitro and ex-vivo models of heart ischemia, employing a rat dental pulp stem cell line (MUR-1) that shares the same ontogenic progenitors with portions of the heart, expresses markers typical of cardiac/vascular-like progenitors and is able to differentiate into cardiomyocytes in-vitro. RESULTS: Here, we demonstrated that the MUR-1 can reach the injured cells/tissue and make contacts with the damaged cardiomyocytes, likely through Connexin 43, N-cadherin and von Willebrand Factor mediated cell-cell interactions, both in in-vitro and ex-vivo models. Furthermore, we found that SDF-1, FGF-2 and HGF, but not VEGF are involved as chemotactic factors in MUR-1 migration, notifying a similarity with neural crest cell behavior during the organogenesis of both the splanchnocranium and the heart. CONCLUSIONS: Herein we found a similarity between what happens during the heart organogenesis and the early migration and homing of MUR-1 cells in ischemic models. GENERAL SIGNIFICANCE: The comprehension of molecular aspects underlying the early phases of stem cell migration and interaction with damaged organ contributes to the future achievement of the coveted stem cell-mediated organ regeneration and function preservation in-vivo.

WITHDRAWN: Activity of endothelial factors on myocardial inotropy.

Ahead of Print article withdrawn by publisher.

Low concentrations of an nitric oxide-donor combined with a liposoluble antioxidant compound enhance protection against reperfusion injury in isolated rat hearts.

Nitric oxide (NO) and reactive oxygen species (ROS) are double-edged swords in reperfused hearts. The effects of a NO-donor and an antioxidant compound against ischemia/reperfusion were studied. The compounds were tested separately, as a mixture and as a new hybrid molecule containing both leads. Isolated rat hearts underwent 30 min global ischemia and 2 hrs reperfusion. Compounds were infused either at 1 or 10 microM concentrations during the first 20 min of reperfusion. Hybrid was also tested in the presence of mitochondrial K(+) ATP-sensitive (mKATP) channel blockade by 5-HD (100 microM). Reduction of infarct size and recovery of left ventricular developed pressure during reperfusion were evaluated. When given at 1 microM concentration, hybrid significantly improved all indices of protection; its beneficial effects were abolished by mKATP channel blockade. At the same concentration, mixture and NO-donor alone improved recovery of left ventricular developed pressure but did not reduce infarct size; antioxidant was ineffective. When given at 10 microM concentration, antioxidant and mixture improved all parameters of protection; NO-donor and hybrid were ineffective. Our data suggest that different signaling cascades could be elicited by low and high concentrations of antioxidant compound and/or NO-donor. It is likely that a different NO-induced release of reactive oxygen species via mKATP channel activation may play a pivotal role in affecting infarct size and post-ischemic contractile recovery.

Nitric oxide and cardiac function.

Nitric oxide (NO) participates in the control of contractility and heart rate, limits cardiac remodeling after an infarction and contributes to the protective effect of ischemic pre- and postconditioning. Low concentrations of NO, with production of small amounts of cGMP, inhibit phosphodiesterase III, thus preventing the hydrolysis of cAMP. The subsequent activation of a protein-kinase A causes the opening of sarcolemmal voltage-operated and sarcoplasmic ryanodin receptor Ca(2+) channels, thus increasing myocardial contractility. High concentrations of NO induce the production of larger amounts of cGMP which are responsible for a cardiodepression in response to an activation of protein kinase G (PKG) with blockade of sarcolemmal Ca(2+) channels. NO is also involved in reduced contractile response to adrenergic stimulation in heart failure. A reduction of heart rate is an evident effect of NO-synthase (NOS) inhibition. It is noteworthy that the direct effect of NOS inhibition can be altered if baroreceptors are stimulated by increases in blood pressure. Finally, NO can limit the deleterious effects of cardiac remodeling after myocardial infarction possibly via the cGMP pathway. The protective effect of NO is mainly mediated by the guanylyl cyclase-cGMP pathway resulting in activation of PKG with opening of mitochondrial ATP-sensitive potassium channels and inhibition of the mitochondrial permeability transition pores. NO acting on heart is produced by vascular and endocardial endothelial NOS, as well as neuronal and inducible synthases. In particular, while in the basal control of contractility, endothelial synthase has a predominant role, the inducible isoform is mainly responsible for the cardiodepression in septic shock.

Endothelial cytochrome P450 contributes to the acetylcholine-induced cardiodepression in isolated rat hearts.

AIMS: Acetylcholine (ACh) is known to reduce the contractility of the heart by acting on myocardial muscarinic M2 receptors. ACh induces also an endothelial-dependent vasodilatation by causing the release of nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factors from the vascular endothelium. It has been proposed that ACh elicits a hyperpolarization of the coronary endothelial cells which may be accompanied by the activation of cytochrome P450 (CYP) and the resulting release of epoxyeicosatrienoic acids (EETs). The study aims at investigating whether endothelial CYP is involved in the cardiodepression by ACh. METHODS AND RESULTS: In isolated rat hearts, cardiodepression by ACh (i.e. 25-30% reduction of developed left ventricular pressure) was partially attenuated either by inhibition of CYP with 1-aminobenzotriazole (ABT) or by endothelial dysfunction obtained with Triton X-100. No attenuation of cardiodepression was seen after nitric oxide synthase and cyclooxygenase inhibition by L-nitro-arginine methyl ester and indomethacin, respectively. CONCLUSION: The results suggest that the negative inotropic effect of ACh depends not only on a direct myocardial effect but also on the endothelial CYP activation.

Mitochondrial ATP-sensitive channel opener does not induce vascular preconditioning, but potentiates the effect of a preconditioning ischemia on coronary reactive hyperemia in the anesthetized goat.

Preconditioning ischemia (PI) increases the speed of the initial vasodilatation (vascular preconditioning) of a subsequent coronary reactive hyperemia (CRH) and reduces total hyperemic flow (THF). We investigated whether changes in CRH similar to those induced by PI are obtained with diazoxide, a mitochondrial ATP-sensitive K+ channel opener, and whether diazoxide influences the effects of a subsequent PI on CRH. In anesthetized goats, flow was recorded from the left circumflex coronary artery (LCCA). CRH and PI were obtained with 15-s and 5-min LCCA occlusions, respectively. CRH was studied before and after PI, before and after diazoxide (2.5 mg/kg i.v.) as well as before and after PI was induced after diazoxide pre-treatment. After PI, the time to peak (ttp) of CRH and THF decreased by 51+/-13% and 23+/-8%, respectively. Diazoxide did not change CRH. After diazoxide and PI, when basal flow had returned to the control level, the ttp of CRH was reduced as after PI alone (-45+/-12%), whereas THF was reduced to a greater extent (-41+/-9% versus -23+/-8%; P<0.01). In conclusion, PI alters CRH by decreasing THF and reducing the ttp of CRH. Whilst diazoxide does not reproduce the effects of PI on CRH, pre-treatment with diazoxide potentiates the effects of PI on THF.

Involvement of nitric oxide in ischemic preconditioning.

In ischemic preconditioning, nitric oxide (NO) limits the extension of a subsequent infarct and protects against ischemia/reperfusion-induced endothelial dysfunction, arrhythmias and myocardial stunning. The protective activity concerns both the first and the second window of protection. The antiarrhythmic effect is attributed to microvessel dilation and to the production of cyclic guanosine monophosphate in the myocardium. The limitation of the infarct size is likely to depend on the opening of the mitochondrial adenosine triphosphate-sensitive potassium channels, to which NO participates via the activation of a protein kinase C (PKC). The endothelial protection involves an NO-mediated reduction in neutrophil adherence to the coronary endothelium and platelet aggregation and is accompanied by an enhanced response to vasodilator stimuli. During preconditioning ischemia, NO is released from the coronary endothelium as a result of bradykinin-induced activation of B2 endothelial receptors. In addition to the early protection, endothelium-derived NO is also responsible for a signaling cascade which leads to the activation of myocardial inducible NO synthase, which in turn is responsible for the release of NO involved in the delayed protection. The signaling cascade includes the activation of PKC-epsilon, tyrosine kinase and some mitogen-activated protein kinases. It has been suggested that the activation of PKC-epsilon is mediated by peroxynitrite produced by the combination of NO and the superoxide anion, the latter being generated during reperfusion which follows preconditioning ischemia.

Ischemic preconditioning: from the first to the second window of protection.

In many species one or more brief coronary occlusions limit the injuries which a subsequent ischemia-reperfusion can produce in the myocardium. A similar protection has been observed in the majority of organ systems. A first period or window of protection can lasts up to 3 hours and is followed by a second window of protection (SWOP) which begins about 24 hours after the brief coronary occlusions and lasts about 72 hours. Increase of the release of endogenous agents such as adenosine and nitric oxide (NO) may be responsible for both windows through the activation of a protein-kinase C (PKC) which in turn activates ATP sensitive potassium (K+(ATP)) channels. Nitric oxide is also reported to act directly on K+(ATP) channels. Recently, it has been suggested that the channels involved in the protection are mitochondrial rather than sarcolemmal. In SWOP the origin of NO is attributed to the activity of an inducible NO-synthase. Free oxygen radicals released during preconditioning are likely to take part in the delayed protection through the production of peroxynitrite which activates PKC and through the increase of the activity of antioxidant enzymes such as Mn superoxide-dismutase. The production of heat shock proteins is considered a marker rather than a mechanism of SWOP.

The endothelium-derived hyperpolarizing factor: does it play a role in vivo and is it involved in the regulation of vascular tone only?

Several investigations performed in vitro have shown that vascular endothelia can release diffusible compounds capable of inducing hyperpolarization of the smooth muscle fibers. Experiments in vitro have shown that these compounds can cause coronary vasodilation and alter cardiac performance. Experiments in vivo only showed the occurrence of vasodilation. While it has been shown that the release of these endothelium-derived hyperpolarizing factors (EDHFs) is not impaired by the inhibition of nitric oxide synthase and cyclooxygenase, the precise nature of the compound(s) has not yet been identified. It is possible that they vary depending on the organ and animal species. However, a common feature of the activity of EDHFs is the activation of calcium-dependent potassium channels, inhibitable by charybdotoxin and apamin. Furthermore in the coronary circulation of many species EDHF seems to be a cytochrome P450-dependent non-prostanoid metabolite of arachidonic acid activated by a number of chemical and physical stimuli similar to those which are known to activate endothelial nitric oxide synthase. Using compounds which inhibit cytochrome P450 and blockers of the calcium-dependent potassium channels, researchers can study the physiological and pathophysiological relevance of EDHF in vivo thus disclosing the potential therapeutic applications of the basic knowledge in this field.

Model-based assessment of pressure and flow-dependent coronary responses following abrupt pressure drops.

The response of the coronary vasculature to an experimental manoeuvre of step-like decrease of the perfusion pressure has been investigated with a model. The coronary vasculature was simulated using a 'windkessel' scheme. Proximal resistance and compliance were assumed to be pressure-independent. The distal resistance, on the contrary, was controlled by a feed-back loop which accounts for the smooth muscle activation induced by the pressure variation. Three more parameters were introduced, and namely the smooth muscle activation time constant and the pressure-induced and flow-induced gains. The parameter values were assessed by comparing the model predicted coronary flow with the one actually measured in animals.

Systolic and diastolic changes in human coronary blood flow during Valsalva manoeuvre.

Valsalva manoeuvre is reported to be sometimes successful for the relief of angina pectoris. The present study investigated how haemodynamic changes produced by Valsalva manoeuvre can interact to improve the relationship between cardiac work and coronary blood flow. Ten male subjects aged 53 +/- 12 years (SD) were considered. Blood velocity in the internal mammary artery, previously anastomosed to the left descending coronary artery, was studied with Doppler technique. The subjects performed Valsalva manoeuvres by expiring into a tube connected to a mercury manometer, to develop a pressure of 40 mmHg. The arterial blood pressure curve was continuously monitored with a Finapres device from a finger of the left hand. During expiratory effort, an increase in heart rate and a decrease in arterial pulse pressure were followed by a more delayed and progressive increase in mean and diastolic pressures. Systolic blood velocity markedly decreased along with the reduction in pulse pressure and increase in heart rate. By contrast, diastolic and mean coronary blood velocities did not show any significant change. Since it is known that the Valsalva manoeuvre strongly reduces stroke volume and cardiac output, it is likely that a reduction in cardiac work also takes place. Since in diastole, i.e. when the myocardial wall is better perfused, coronary blood velocity did not show any significant reduction, it is likely that unchanged perfusion in the presence of reduced cardiac work is responsible for the relief from angina sometimes observed during Valsalva manoeuvre. It is also likely that the increase in heart rate prevents the diastolic and mean blood coronary velocity from decreasing during the expiratory strain, when an increased sympathetic discharge could cause vasoconstriction through the stimulation of the coronary alpha-receptors.

Italian high altitude laboratories: past and present.

Italy is a mountainous country with a total of 88 huts and bivouacs at altitudes higher than 3,000 m. Starting in the 19th century a great deal of research in high altitude pathophysiology has been carried out in Italy and many Italian physicians have been involved in mountain medicine. Most of the Italian research has been carried out at two locations: the scientific laboratories "Angelo Mosso" on Monte Rosa (Capanna Regina Margherita and Laboratorio Angelo Mosso), and the "Pyramid" in Nepal. The Capanna Regina Margherita, located on the top of Punta Gnifetti (Monte Rosa, 4,559 m), was inaugurated in 1893. With the support of Queen Margherita of Savoy, an Observatory for scientific studies was built beside this hut in 1894. In 1980 the hut was completely rebuilt by the Italian Alpine Club. The Istituto Angelo Mosso at Col d'Olen, at the base of Monte Rosa (at 2,900 m) was inaugurated in 1907. The high altitude laboratory named the "Pyramid" was built in 1990. Made of glass and aluminium, this pyramid-shaped structure is situated in Nepal at 5,050 m. The scientific laboratories "Angelo Mosso" on Monte Rosa (mainly the Capanna Regina Margherita) and the Pyramid form a nucleus for high altitude research: the former is especially devoted to research regarding acute mountain sickness and the response to subacute hypoxia, whereas the latter is a unique facility for research responses to chronic hypoxia, the effect of exposure to very high altitude, and the study of the resident population living in the Himalayas for at least 25,000 years.

New insights into nitric oxide and coronary circulation.

Since its discovery over 20 years ago as an intercellular messenger, nitric oxide (NO), has been extensively studied with regard to its involvement in the control of the circulation and, more recently, in the prevention of atherosclerosis. The importance of NO in coronary blood flow control has also been recognized. NO-independent vasodilation causes increased shear stress within the blood vessel which, in turn, stimulates endothelial NO synthase activation, NO release and prolongation of vasodilation. Reactive hyperemia, myogenic vasodilation and vasodilator effects of acetylcholine and bradykinin are all mediated by NO. Ischemic preconditioning, which protects the myocardium from cellular damage and arrhythmias, is itself linked with NO and both the first and second windows of protection may be due to NO release. Exercise increases NO synthesis via increases in shear stress and pulse pressure and so it is likely that NO is an important blood flow regulatory mechanism in exercise. This phenomenon may account for the beneficial effects of exercise seen in atherosclerotic individuals. Whilst NO plays a protective role in preventing atherosclerosis via superoxide anion scavenging, risk factors such as hypercholesterolemia reduce NO release leading the way for endothelial dysfunction and atherosclerotic lesions. Exercise reverses this process by stimulating NO synthesis and release. Other factors impacting on the activity of NO include estrogens, endothelins, adrenomedullin and adenosine, the last appearing to be a compensatory pathway for coronary control in the presence of NO inhibition. These studies reinforce the pivotal role played by the substance in the control of coronary circulation.

Ischaemic preconditioning changes the pattern of coronary reactive hyperaemia in the goat: role of adenosine and nitric oxide.

OBJECTIVES: After ischaemic preconditioning (IP), obtained by short episodes of ischaemia, cardiac protection occurs due to a reduction in myocardial metabolism through the activation of A1 adenosine receptors. The antiarrhythmic effect of IP is attributed to an increase in the release of nitric oxide (NO) by the endothelium. On the basis of the above consideration the present investigation studies the changes induced by preconditioning in coronary reactive hyperaemia (RH) and how blockade of A1 receptors and inhibition of NO synthesis can modify these changes. METHODS: In anaesthetised goats, an electromagnetic flow-probe was placed around the left circumflex coronary artery. Preconditioning was obtained with two episodes of 2.5 min of coronary occlusion, separated by 5 min of reperfusion. RH was obtained with a 15 s occlusion. In a control group (n = 7) RH was studied before and after IP. In a second group (n = 7), 0.2 mg kg-1 of 8-cyclopentyl-dipropylxanthine, an A1 receptor blocker, and in a third group (n = 7) 10 mg kg-1 of NG-nitro-L-arginine (LNNA), an NO inhibitor, were given before IP. Reactive hyperaemia was again obtained before and after IP. RESULTS: In the control group, after IP, the time to peak hyperaemic flow and total hyperaemic flow decreased by about 50% and 25%, respectively. The A1 receptor blockade alone did not change RH. During A1 blockade, IP reduced the time to peak of RH similar as in control (45%), but did not alter total hyperaemic flow. LNNA alone reduced resting flow and total hyperaemic flow. After NO inhibition, IP only reduced total hyperaemic flow by about 15%, but the time to peak flow was not affected. CONCLUSIONS: IP alters RH by decreasing total hyperaemic flow and reducing the time to peak hyperaemic flow. While the former effect is attributed to a reduction in myocardial metabolism through the activation of the A1 receptors, the latter is likely to be due to an increased endothelial release of NO, suggesting that in addition to a protective effect on the myocardium, IP also exerts a direct effect on the responsiveness of the coronary vasculature (vascular preconditioning).

Systolic coronary flow impediment in the dog: role of ventricular pressure and contractility.

The present study was planned to investigate the effect of left ventricular pressure and inotropic state on coronary arterial inflow in systole in the anaesthetized dog. A wide range of left ventricular systolic pressures, including the physiological range, were studied. Experiments were done under conditions of maximal vasodilatation and low perfusion pressure in order to avoid vascular autoregulative interference and to keep the microvascular pressure within the normal range. In five anaesthetized dogs, perfused with extracorporeal circulation system, ventricular volume was changed from 20 to 50 ml in steps of 10 ml by filling an intraventricular latex balloon, and the related changes in left ventricular pressure and coronary flow were measured. The volume was then extended to 70 ml to obtain an overstretch which induced a transient decrease in cardiac contractility. During the period of low cardiac contractility the volume was brought back to 20 ml in steps of 10 ml. Systolic ventricular pressure changed with volume but was lower during the period of low contractility. For systolic pressures below 100 mmHg there was no significant relationship between pressure and coronary systolic flow, but the relationship shifted to higher flows during low contractility. For systolic pressures above 100 mmHg systolic coronary flow decreased significantly when systolic pressure increased. In this case the slopes of the relationships were not significantly different before and after the reduction in contractility. These findings suggest that for systolic pressures less than 100 mmHg (i.e. below the physiological range) the shielding effect of the contracting ventricle prevents the ventricular pressure from being transmitted in the myocardial wall. When systolic pressure exceeds 100 mmHg the shielding effect is overcome and the amplitude of the systolic flow reduction varies with ventricular pressure.

Effect of generalised sympathetic activation by cold pressor test on cerebral haemodynamics in healthy humans.

There is no general agreement regarding several aspects of the role of the sympathetic system on cerebral haemodynamics such as extent of effectiveness, operational range and site of action. This study was planned to identify the effect of a generalised sympathetic activation on the cerebral haemodynamics in healthy humans before it is masked by secondary corrections, metabolic or myogenic in nature. A total of 35 healthy volunteers aged 20-35 underwent a 5 min lasting cold pressor test (CPT) performed on their left hand. The cerebral blood flow (CBF) velocity in the middle cerebral arteries and arterial blood pressure were recorded with transcranial Doppler sonography and with a non-invasive finger-cuff method, respectively. The ratio of arterial blood pressure to mean blood velocity (ABP/Vm) and Pulsatility Index (PI) were calculated throughout each trial. CPT induced an increase in mean ABP (range 2-54 mmHg depending on the subject) and only a slight, though significant, increase in blood velocity in the middle cerebral artery (+2.4 and +4.4% on ipsi- and contralateral side, respectively). During CPT, the ratio ABP/Vm increased and PI decreased in all subjects on both sides. These changes began simultaneously with the increase in blood pressure. The increase in ABP/Vm ratio is attributed to an increase in the cerebrovascular resistance, while the concomitant reduction in PI is interpreted as due to the reduction in the compliance of the middle cerebral artery. The results suggest that generalised increases in the sympathetic discharge, causing increases in ABP, can prevent concomitant increases in CBF by acting on both small resistance and large compliant vessels. This effect is also present when a slight increase in blood pressure occurs, which suggests a moderate increase in the sympathetic discharge, i.e. when ABP remains far below the upper limit of CBF autoregulation.

[Mechanisms of ischemic preconditioning: relation with ischemia-reperfusion injury]. / Meccanismi del precondizionamento ischemico: relazione con i danni da ischemia-riperfusione.

If a coronary occlusion long enough to produce a myocardial infarction is preceded by one or more brief periods of occlusion, the infarct size is reduced with respect to the area at risk. Also the ischaemia reperfusion injury is remarkably reduced. Such effects form the ischaemic preconditioning. Ischaemia-reperfusion injury is attributed to a Ca2+ overload of the myocardial fibres together with an inadequate resynthesis of ATP, a loss of membrane phospholipids and a release of free oxygen radicals. The inadequate resynthesis of ATP is responsible for an increased concentration of nucleosides and purinic bases with swelling of the myocardial fibres. The cell Ca2+ overload depends on a reduced activity of the ionic pumps caused by the oxygen lack during ischaemia. During reperfusion the vascular endothelial cells of the previously ischaemic area release free oxygen radicals in response to the activity of the xanthine-oxidase on hypoxanthine produced by the ischaemic myocardium. This initial release of oxygen radicals is responsible for the adhesion of neutrophils to the endothelium. After adhesion also the neutrophils release free radicals due to the activity of NADPH-oxidase on molecular oxygen. Myocardial, neural and endothelial mechanisms account for the protective effect of preconditioning. Myocardial mechanisms include the release of adenosine as well as of antioxidant enzymes. Adenosine, which activates protein-kinase C, favours the phosphorylation of a protective protein, whereas the antioxidant enzymes impair the activity of the free oxygen radicals. Preconditioning may also involve the synthesis of a heat shock protein. Neural mechanisms are represented by a reduced release of noradrenaline from the sympathetic nerve endings and a reduced sensitivity of myocardium to noradrenaline. Finally, vascular endothelial cells take part in preconditioning by means of an increased production of nitric oxide which seems to exert a protection against arrhythmias.

The Gaboon viper, Bitis gabonica: hemorrhagic, metabolic, cardiovascular and clinical effects of the venom.

The effects of Bitis gabonica venom have been studied in several animal species, including the monkey, dog, rabbit, rat and guinea pig. Further information has been provided by observations on the effects of snake bite in man. Bitis gabonica venom exerts a number of cytotoxic and cardiovascular effects: cytotoxic effects include widespread hemorrhage, caused by the presence of two hemorrhagic proteins. These hemorrhagins bring about separation of vascular endothelial cells and extravasation of blood into the tissue spaces. Metabolic alterations include decreased oxygen utilization by tissues and increased plasma glucose and lactate concentrations. Metabolic non-compensated acidosis has also been seen in the rat as a consequence of the cytotoxicity of the venom. Cardiovascular effects include disturbances in atrio-ventricular conduction and reduction in amplitude and duration of the action potential brought about by a decreased calcium membrane conductance. A progressive decrease in myocardial contractility can also be attributed to the decreased calcium conductance, which together with the severe acidosis may cause death in experimental animals. A severe, though reversible, vasodilatation was observed after envenomation due to unidentified compounds in the venom. In man, envenomation causes a variable clinical picture depending on the time course and severity of envenomation. Frequently seen effects include hypotension, hemorrhage at the site of the bite and elsewhere and disseminated intravascular coagulation. Envenomation can be satisfactorily treated with antivenom.