Histamine H3-receptor stimulation is unable to modulate noradrenaline release by the isolated rat heart during ischaemia-reperfusion

The aim of this study was to evaluate the ability of H3-histaminergic prejunctional receptors to modulate the noradrenaline release induced by myocardial ischaemia in the rat, and the effects of an eventual modulation on haemodynamic, biochemical and electrophysiological parameters. Isolated rat hearts were perfused according to the Langendorff technique. Control hearts (n = 13) were not treated; two groups were treated with the H3-agonist R-alpha-methyl-histamine at 0.3 microM (n = 14) and 1 microM (n = 11) and one group, used as positive control, was treated with the selective alpha 2-agonist Mivazerol at 0.5 microM (n = 14) added to the perfusion medium. Noradrenaline, lactate and transaminase output in the coronary effluent, as well as various haemodynamic and electrophysiological parameters, were measured during global and total ischaemia (30 min) and reperfusion (30 min). alpha 2-receptor stimulation increased ischaemia-induced noradrenaline release during reperfusion (195 +/- 13 vs. 145 +/- 12 pmol.g-1 in control group, P < 0.05). In contrast, R-alpha-methyl-histamine, at both doses, did not significantly modify these parameters. Both treatments did not affect ischaemia- and reperfusion-induced haemodynamic (decrease in heart rate or in left ventricular developed pressure), biochemical (lactate and GOT release) and electrophysiological (arrhythmias or increase in action potential duration) alterations. Unlike other species, the rat appears to be insensitive to H3-histaminergic receptor modulation of ischaemia-induced noradrenaline release, although a modulation can be seen with other prejunctional receptor agonists.     

Met5-enkephalin-Arg6-Phe7 (MEAP): A Cardioprotective Hormonal Opioid

Background: Acute myocardial ischemia is an important cause of morbidity and mortality worldwide. The heart and other organs can be rendered more resistant to the deleterious effects of ischemia through a variety of preconditioning strategies, including treadmill exercise and brief ischemia of skeletal muscle. Some of the beneficial effects of these preconditioning strategies appear to be mediated by as‐of‐yet unidentified hormonal opioids. Objectives: To test the hypothesis that endogenous opioids of the enkephalin class are capable of improving ischemic tolerance and acting in a hormonal manner. Methods: In phase one of the investigation, the authors assessed the cardioprotective potential of all four known enkephalins. This was achieved by subjecting isolated buffer‐perfused rabbit hearts to a 25‐minute period of test ischemia and two hours of reperfusion (protocol 1) after receiving treatment with either saline vehicle (controls) or increasing concentrations of purified enkephalins. On the basis of results from these initial studies, the authors performed additional experiments (protocol 2) to determine whether Met⁵‐enkephalin‐Arg⁶‐Phe⁷ (MEAP) could be absorbed from skeletal muscle and exert a cardioprotective effect. Specifically, MEAP or vehicle (controls) was given intramuscularly 24 hours before the hearts were harvested. A similar assessment of ischemic tolerance as described in protocol 1 was then performed. Postischemic myocardial viability (infarct size) was assessed in all cases by triphenyltetrazolium chloride (TTC) staining. Hemodynamic parameters and infarct sizes for concentration‐dependence studies were compared by two‐way analysis of variance, and infarct sizes from protocol 2 studies were compared by using Student's t‐test (significance set at p ≤ 0.05). Results: Mean infarct size in control hearts (± SEM) was 33% (± 4%) and 36% (± 6%) for protocol 1 and 2, respectively. Of the four enkephalins tested in protocol 1, only MEAP treatment showed a tendency toward cardioprotection. Interestingly, an alternative enkephalin, methionine⁵‐enkephalin‐Arg⁶‐Gly⁷‐Leu⁸, tended to exert an injurious effect. In protocol 2, MEAP treatment 24 hours before ischemia significantly reduced infarct size (14%± 4%) compared with controls, suggesting that it can be released from muscle and exert a distant cardioprotective effect. Conclusions: When given either directly to the heart or absorbed from a distant tissue, MEAP induces cardioprotection, supporting the hypothesis that it can act as a hormonal modulator of ischemic tolerance.     

Amiodarone offsets the cardioprotective effects of ischaemic preconditioning against ischaemia/reperfusion injury

Both ischaemic preconditioning (IPC) and amiodarone protect against myocardial ischaemia. We examined whether a combination of IPC and amiodarone demonstrated an additive protective effect in isolated rat hearts (n = 40). The controls (group I) were subjected to ischaemia/ reperfusion injury; group II was subjected to cycles of IPC prior to ischaemia/ reperfusion injury; group III was subjected to ischaemia in the presence of amiodarone (10(-10) mol/1); and group IV was subjected to IPC followed by ischaemia in the presence of amiodarone (10(-10) mol/l). Amiodarone produced the best preserved left ventricular end-systolic pressure and dP/dtmax, less developed ventricular stiffness, the shortest arrhythmia duration, and the smallest infarct size among the groups. All of the myocardial protective effects against ischaemia/reperfusion injury were diminished or abolished when IPC and amiodarone were applied sequentially.     

Myocardial protection by volatile anesthetics

Myocardial ischaemia/reperfusion situations may occur during the perioperative period. The cardioprotective effects of anaesthetics have been known for a long time: volatile anaesthetics reduce the ischaemic cell damage and infarct development. Besides ischaemia, reperfusion itself can also lead to cellular damage, thereby further increasing the ischaemic injury (reperfusion injury). Inhalational anaesthetics offer specific protective effects against reperfusion injury in isolated hearts as well as in rabbit hearts in vivo. This protection does not depend on haemodynamic side-effects of the substances and is even present after protecting the heart against ischaemic damage using a cardioplegic solution. Short periods of ischaemia render the myocardium resistant to subsequent longer periods of ischaemia. This strongest endogenous protective mechanism against the consequences of an ischaemia is known as ischaemic preconditioning. The protective effect can also be produced by stimulation of different types of receptors: the respective agonists produce pharmacological (chemical) preconditioning. The common pathway of the signal transduction cascade of both ischaemic and chemical preconditioning includes the sarcolemnal and/or mitochondrial ATP-sensitive potassium channel. Volatile anaesthetics can imitate the protective effects of a short ischaemia, thereby producing chemical preconditioning. This effect depends, at least in part, on anaesthetic-induced opening of ATP-sensitive potassium channels.     

New evidence for the role of TNF-alpha in liver ischaemic/reperfusion injury

Background Tumour necrosis factor‐alpha (TNF‐α) plays a key role in causing ischaemia/reperfusion (I/R) injury. I/R also causes activation of xanthine oxidase and dehydrogenase (XDH + XO) system that, via generated free radicals, causes organ damage. We investigated the effect of ischaemia, reperfusion and non‐ischaemic prolonged perfusion (NIP) on TNF‐α and XDH + XO production in an isolated perfused rat liver model. Materials and methods Rat livers underwent 150 min NIP (control group) or two hours of ischaemia followed by reperfusion (I/R group). TNF‐α (TNF‐α mRNA and protein level), XDH + XO production and bile secretion were determined in tissue and effluent at baseline, at 120 min of ischaemia, after 30 min of reperfusion (I/R group) and after 120 and 150 min of prolonged perfusion (control). Results Unexpectedly, neither ischaemia nor reperfusion had any effect on TNF‐α production. TNF‐α in effluent was 11 ± 4·8 pg mL^?1 at baseline, 7 ± 3·2 pg mL^?1 at the end of ischaemia, and 13 ± 5·3 pg mL^?1 after 30 min of reperfusion. NIP, however, caused a significant increase of TNF‐α synthesis and release. TNF‐α effluent level after 120 and 150 min of perfusion was 392 ± 78·7 pg mL^?1 and 408 ± 64·3 pg mL^?1, respectively. TNF‐α mRNA in tissue was also significantly elevated compared to baseline levels (1·31 ± 0·2 P < 0·001 and 1·38 P < 0·002, respectively). Decrease of liver function (expressed by bile secretion) during I/R and NIP was accompanied by significant XDH + XO elevation. Conclusion This is the first evidence that NIP, and not I/R, is the decisive trigger for TNF‐α production. This study leads to a better understanding of pathogenesis of liver I/R and perfusion damage.     

Tonic block of the Na+ current in single atrial and ventricular guineapig myocytes, by a new antiarrhythmic drug, Ro 22-9194

Summary— Ro 22-9194 reduced the Na⁺ current in the atrial myocytes as well as ventricular myocytes in a tonic block fashion. Ro 22-9194 had a higher affinity to the inactivated state Na⁺ channels (Kd₁ = 3.3 μM in atrial myocytes, Kd₁ = 10.3 μM in ventricular myocytes) than to those in the rested state (Kd_R = 91 μM in atrial myocytes, Kd_R = 180 μM in ventricular myocytes), which indicated that Ro 22-9194 had a higher affinity to the Na⁺ channels in atrial myocytes than in ventricular myocytes. Ro 22-9194 shifted the inactivation curve in the hyperpolarized direction in both atrial and ventricular myocytes. These findings suggest that Ro 22-9194 more strongly inhibited the Na⁺ channel of the atrial myocytes of the diseased hearts with the depolarized membranes potentials than the Na⁺ channels in ventricular myocytes.     

Influence of a selective 5HT1-receptor agonist GR43175 on platelet responsiveness

The possible interaction of sumatriptan, a selective 5HT₁-receptor agonist, with platelet responsiveness has been investigated. Stimulation of platelet rich plasma with sumatriptan (1–100 μM) did not induce shape change, aggregation or modification of intraplatelet cytosolic calcium levels. Total inhibition of aggregation induced by 20 μM 5HT was observed in platelets preincubated for 20 min with 100 μM sumatriptan. In the same model, platelet stimulation with 4 μM adenosine 5'-diphosphate (ADP), concentration known to induce an irreversible single-phase curve, determined a decrease of aggregatory response. Concentrations from I μM to 50 μM of sumatriptan did not influence the aggregatory response induced by 5HT and ADP. These effects appear not to be determined by modifications of platelet calcium homeostasis. The possibility to modulate platelet responsiveness by sumatriptan offers a further approach for evaluating the probable link between platelet behaviour and pathophysiology of migraine.     

Effects of prostaglandin-E1 on ST segment elevation and regional myocardial blood flow during experimental myocardial ischaemia in dogs

Abstract. The effects of prostaglandin E₁ (PGE₁) on myocardial ischaemia (as measured by epicardial ST segment changes), myocardial flow and substrate exchange has been studied in dogs. Myocardial ischaemia was induced by intermittent external clipping of a branch of the left anterior descending coronary artery.
During occlusion with a continuous intravenous infusion of isoprenaline, elevated epicardial ST segments (∑ST), were raised to 46 ± 6 mV (mean ± SEM). Pretreatment with PGE₁ reduced ∑ST to 34 ± 6 mV ( P <0.001), but had no effect on mean aortic blood pressure (AP¯) or on regional myocardial blood flow. Isoprenaline infusion increased plasma free fatty acids (FFA) to 1925 ± 150 μmol/l and this was reduced to 1320 ± 220 μmol/l by PGE₁ ( P <0.005).
During occlusion without isoprenaline, PGE₁ did not effect ∑ST or plasma FFA when infused intravenously or into the left atrium. Mean aortic blood pressure decreased from 131 ± 7 to 108 ± 10 (PGE₁ i.v.) or 109 ± 8 mmHg (PGE₁ i.a.) ( P <0.001). This was associated with a decrease in regional myocardial blood flow, both in the ischaemic and non-ischaemic myocardium. However, when blood pressure was maintained constant, intravenous PGE₁ tended to decrease occlusion-induced ST segment elevation.
These results suggest that PGE₁ can reduce isoprenaline-stimulated myocardial ischaemia through its antilipolytic action but in the absence of catecholamine stimulation the main effect is to reduce blood pressure thereby counterbalancing any potentially beneficial effects on the ischaemic myocardium.     

Cardioprotective Effects of Red Blood Cells on Ischemia and Reperfusion Injury in Isolated Rat Heart: Release of Nitric Oxide as a Potential Mechanism

BACKGROUND: Circulating cells influence myocardial function during ischemia and reperfusion, (eg, neutrophils exacerbate, and platelets protect the myocardium from deterioration). This study was designed to determine the role of red blood cells on myocardial function following ischemia and reperfusion in isolated rat hearts. METHODS AND RESULTS: Exposure of buffer-perfused hearts to 40 minutes of total ischemia followed by 30 minutes of reperfusion resulted in myocardial dysfunction and injury, indicated by decrease in the force of cardiac contraction (FCC, -25 +/- 4%), increase in the coronary perfusion pressure (CPP, +20 +/- 3%) and decrease in myocardial superoxide dismutase (SOD, 2.5 +/- 0.2 vs 3.5 +/- 0.4 U/mg protein in sham ischemic hearts, P <.05). Perfusion of the hearts with washed rat red blood cells showed significant protective effects against ischemia and reperfusion, indicated by minimal change in FCC (-10 +/- 4%) and CPP (+3 +/- 3%) (both P <.01 vs buffer alone perfused hearts) and preservation of myocardial SOD activity (2.8 +/- 0.4 U/mg protein, P <.05 vs buffer alone perfused hearts). The cardioprotective effects of red blood cells were attenuated when the red blood cells were preincubated with the nitric oxide blood cells were attenuated when the red blood cells were preincubated with the nitric oxide blood cells were attenuated when the red blood cells were preincubated with the nitric oxide synthase inhibitors N(omicron)-nitro-l-arginine (l-NNA, 5 x 10(-4)M) or N(omicron)-nitro-l-arginine methyl ester (l-NAME, 5 x 10(-4)M) at 37 degrees C for 60 minutes before perfusion of the heart. Perfusion of hearts with the nitric oxide precursor l-arginine (2 x 10(-4)M) also exerted significant protective effects on FCC ( - 14 +/- 4%), CPP (+12 +/- 3%) and myocardial SOD activity (2.9 +/- 0.2 U/mg protein) following ischemia and reperfusion. In other studies, washed rat red blood cells expressed nitric oxide synthetase activity which was inhibited by both l-NNA and l-NAME. CONCLUSIONS: These results suggest that red blood cells exert cardioprotective effects against ischemia and reperfusion at least in part by the l-arginine-nitric oxide pathway in isolated rat hearts.     

Effects of cyclooxygenase inhibitors, prostaglandins F2α and I2, on isolated coeliac and basilar arteries of alloxan-diabetic dogs

Abstract. The effects of prostaglandin synthetase inhibitors PGF_2α and PGI₂ on the tone of isolated basilar and coeliac arteries were studied in healthy and alloxan-diabetic dogs. PGF_2α (1 μmol l^-1) produced a significantly higher tone in diabetic basilar arteries (1·15 ± 0·16 mN) than in normal cerebral vessels (0·7 + 0·10 mN). By contrast, the contractile responses of normal and diabetic coeliac arteries to PGF_2α did not differ. The cyclooxygenase inhibitors indomethacin (3 μmol l^-1) and suprofen (0·58 μmol l^-1) potentiated the PGF_2α-evoked contractions in all of the vessels studied. The percent potentiation was greater (50–60%) in the basilar arteries from alloxan-treated dogs than in normal basilar vessels (22–30%). There was not such a difference between diabetic and normal coeliac arteries. Prostacyclin produced a concentration-related relaxation in the presence of indomethacin or indomethacin + PGF_2α. The relaxant potencies of PGI₂ were similar in the vessels from metabolically healthy and diabetic dogs. The IC₅₀ values for PGI₂ were 11·6 ± 1·3 and 11·8 ± 1·8 nmol l^-1 in normal and diabetic basilar arteries, respectively; they were 25·4 ± 3·2 and 26·2 ± 3·9 nmol l^-1 in control and alloxan-treated coeliac vessels. These results indicate that normal and diabetic vessels may have differential reactivity to cyclooxygenase inhibitors, this difference being dependent on the vascular region.     

Effects of K+ channel inhibitors and antagonists on NS-004 evoked relaxations in guinea-pig isolated trachea

Summary— The smooth muscle relaxant responses to NS-004, an activator of charybdotoxin-sensitive, large conductance Ca²⁺-dependent K⁺ channels (BKCa) were studied on the basal spontaneous tone in guinea-pig trachea in vitro. The sensitivity of these responses to a range of K⁺ channel inhibitors and antagonists were also evaluated. NS-004 (0.1–30 μM) evoked concentration-related relaxations (pIC₅₀ 5.48 ± 0.13) on the spontaneous tone in guinea-pig tracheal rings, suspended in Krebs bicarbonate solution, with a maximum response not different to that to aminophylline (1 μM). Charybdotoxin (0.03 and 0.1 μM) or iberiotoxin (0.1 μM) significantly displaced the NS-004 concentration-response curve to the right of control with no change in maximum response. In contrast, glibenclamide (1.0 μM), apamin (0.1 μM) and dofetilide (1.0 μM) each failed to modify the responses to NS-004 on spontaneous tone in guinea-pig trachea. These results suggest that relaxations in guinea-pig tracheal smooth muscle to the substituted benzimidazolone, NS-004, involve the activation of BK_Ca channels.     

Effect of Na+ reduction and monensin on ion content and contractile response in normoxic and ischaemic reperfused rat hearts

Summary— The possibility was explored whether the functional properties of Na+/Ca²⁺ exchange are altered after ischaemia, thereby contributing to the elevated intracellular (i) Ca²⁺ levels in ischaemic reperfused hearts. The intracellular Na+, K+ and Ca²⁺ contents in rat Langendorff heart preparations were determined by atomic absorption spectrometry under normoxic conditions, after ischaemia (30 min) and after ischaemia (30 min) plus reperfusion (30 min). In addition, the influence of modulating the Na+ gradient (Na+_o/Na+_i) across the sarcolemma was studied with respect to cardiac contractility and intracellular ion content. This was done by either decreasing extracellular (o) Na+ or by increasing Na+_i with monensin, both in normoxic and reperfused hearts. Both Na+_o reduction and monensin led to an increase in contractility and coronary flow, an effect which was nearly abolished in reperfused hearts. Under normoxic conditions the intracellular ion contents amounted to Na+ = 12.4 ± 0.4, K+ = 99.0 ± 3.1 and Ca²⁺ = 0.64 ± 0.02 mmol/kg cell (means ± SEM, n = 7). In normoxic hearts, lowering Na+_o reduced and monensin increased Na+_i, thereby both leading to a decrease in Na+ gradient; no effect on total Ca²⁺_i content was observed. Na+_i increased twofold after ischaemia as compared to the normoxic situation, an effect which was aggravated (4 fold increase) in reperfused hearts. The opposite effects were observed for K+_i with a 25% decrease after ischaemia and a 40% decrease in reperfused hearts. Only after ischaemia plus reperfusion was Ca²⁺_i increased (6 fold). In reperfused hearts, lowering Na+_o again reduced and monensin increased Na+_i, whereas a further rise in Ca²⁺_i was now observed depending on the Na+ gradient across the sarcolemma: the larger the drop in Na+ gradient, the more pronounced the increase in Ca²⁺_i in the reperfused heart. We conclude that the Ca²⁺_i increase in reperfused hearts can be modulated by changing the Na+ gradient across the sarcolemma. This suggests that inhibited or reversed Na+/Ca²⁺ exchange is predominantly responsible for the rise in Ca²⁺_i in ischaemic hearts that are subjected to reperfusion.     

Protective role of glutathione on α1 proteinase inhibitor inactivation by the myeloperoxidase system. Hypothetic study for therapeutic strategy in the management of smokers' emphysema

Summary— In smoking subjects with obvious emphysema, the interaction between neutrophil-derived MPO and H₂O₂ produced by alveolar inflammatory cells (alveolar macrophages (AM) and polymorphonuclear neutrophils (PMN)) has the ability to spontaneously inactivate, in vitro , the α₁ proteinase inhibitor (α₁PI). This inactivation can induce a desequilibrium of the protease-antiprotease balance in the lungs. In this study, we investigated the ability of glutathione to protect α₁PI. In a cellular model of α₁PI inactivation mimicking the effects of alveolar inflammatory cells present in the lower respiratory tract of smoking patients with emphysema, we demonstrated that glutathione can protect α₁PI against the oxidative inactivation by these activated cells. This protection has been computed in a cellular experimentation (AM and MPO-system) with a 50% inhibitory concentration of 62 μM. Moreover, glutathione has an important inhibitory effect directly on H₂O₂ released by PMA-stimulated AM (IC₅₀ = 30 μM) or PMA stimulated PMN (IC₅₀ = 70 μM). The mechanism, which governs glutathione may be a result of a scavenging effect on H₂O₂ as demonstrated in a free cellular experiment. With this in vitro demonstrated effectiveness, glutathione as a therapeutic antioxidant, via the aerosol, has been proposed, in order to prevent tissue damage, inflicted by an excess of activated phagocytic cells, in some lung diseases such as smoking patients with emphysema.     

Lack of efficacy of 5-HT2A receptor antagonists to reduce brain damage after 3 minutes of transient global cerebral ischaemia in gerbils

Summary— Stimulation of the 5-HT_2A receptors by serotonin has been reported to exert an excitatory effect on neocortical neurons in rats and mice, to facilitate ischaemia-induced release of excitatory amino acids and to mediate the vasomotor constrictor component of the response of blood vessels to 5-HT. 5-HT_2A receptor antagonists have, therefore, been proposed as potential protectants against the effects of cerebral ischaemia. The aim of this study was to evaluate the effects of two relatively selective 5-HT_2A receptor antagonists, ketanserin and ritanserin, on delayed hyperactivity and the ensuing neuronal degeneration induced by 3 minutes of bilateral carotid artery ligation in Mongolian gerbils. Effects were compared to that of flunarizine, which blocks calcium overload and served as a positive control in this paradigm. Temporal and/or rectal temperatures were measured and strictly controlled during the ischaemia and the early reperfusion phase. Locomotor activity was measured one day after the ischaemia and neuronal degeneration quantified 7 days later using an image analysis system (Quantimet 570, Leica). Global ischaemia in gerbils elicits hyperactivity associated with a delayed neuronal degeneration predominantly in the CA1 zone of the hippocampus. Ketanserin and ritanserin (3 and 10 mg/kg ip, twice daily for 3 days, pre- and postischaemia) did not protect the CA1 neurons against ischaemic damage. The postischaemic hyperactivity was inhibited only with the higher dose of ketanserin. As previously reported, flunarizine (30 mg/kg po) markedly reduced neuronal degeneration (-44.2%, p < 0.01) and totally abolished the ischaemia-induced hyperactivity. These data demonstrate that ketanserin and ritanserin are not effective protectants of the gerbil hippocampus against ischaemic damage when the body temperature of the animals is controlled, thus suggesting that 5-HT_2A receptors are not directly implicated in the pathogenesis of global cerebral ischaemia in this model.     

α1 and α2-adrenergic control of large and small coronary arteries during exercise in conscious dogs under β-blockade

Summary— The aim of this study was to determine the relative roles of α₁-and α₂-adrenoceptors at the level of large epicardial and small resistance coronary arteries when sympathetic tone is increased by exercise in conscious dogs. The responses of left circumflex coronary artery diameter and blood flow were investigated at rest and during graded treadmill exercise (5, 10 and 12 km/h) in six chronically instrumented dogs during control conditions (saline) and after administration of propranolol (1 mg/kg) either alone or in combination with either prazosin (50 μg/kg), or idazoxan (300 μg/kg), or the association of prazosin + idazoxan (same doses). In control conditions, graded treadmill exercise resulted in a progressive increase in coronary artery diameter (+ 3.8 ± 0.6% from 3479 ± 80 μm) and in a decrease in coronary vascular resistance (- 46.0 ± 4.5% from 8.49 ± 1.51 mmHg/cm/s). Propranolol significantly constricted large (- 4.4 ± 0.6% from 3486 ± 87 μm) and limited dilation of small coronary arteries during exercise. These coronary effects of propranolol remained unchanged following additional α₂-adrenoceptor blockade by idazoxan but were abolished following α₁-adrenoceptor blockade by prazosin, given either alone or combined with idazoxan. Thus, α₁- but not α₂-adrenoceptors are responsible for propranolol-induced constriction of large coronary arteries and limitation of small coronary arteries dilation during exercise in conscious dogs.     

Role of Na+-H+ Exchange on Reperfusion Related Myocardial Injury and Arrhythmias in an Open-Chest Swine Model

The inhibition of Na⁺-H⁺ exchange (NHE) with amiloride analogues in vitro has been shown to prevent reperfusion arrhythmias and additional cell necrosis. Inhibition of intracellular Ca²⁺ overload via NHE inhibition has been suggested as a mechanism of these protective effects. The aim of this study was to examine whether treatment with amiloride analogues reduces the incidence of reperfusion arrhythmias and limits infarct size in vivo. Open-chest swine were exposed to a 30-minute left anterior descending artery (LAD) occlusion and 180 minutes of reperfusion during atrial pacing at 150 ppm. Intravenous 5-(N,N-dimethyI)-amiloride (AML, 5 μg/kg per min) was administered in the treatment group (n = 7) and intravenous saline in the control group (n = 7), starting 10 minutes before coronary occlusion. The infusion was continued during ischemia and reperfusion. The area at risk was defined by monastral blue dye and infarct size by triphenyltetrazolium chloride staining. Limb leads ECG and monophasic action potentials (MAPs) from the epicardium in the ischemic area were recorded. There was no significant difference in the size of the area at risk and hemodynamic parameters between the groups. However, the infarcted area was 0.4%± 1.0% of the area at risk in the treatment group, whereas it was 62%± 29% in the control group (P < 0.05). Pathological examination (Hematoxylin-eosin and mallory s phosphotungstic acid-hematoxylin staining) revealed that all of the infarcted area consisted of contraction band necrosis. MAP duration in both groups was significantly shortened during ischemia. After reperfusion, MAP duration in the treatment group recovered earlier than that of control group. However, there was no significant difference in the incidence of ventricular tachyarrhythmia between the groups. Inhibition of NHE with AML prevented reperfusion related cell necrosis in the in vivo swine model, but did not reduce the incidence of ventricular tachyarrhythmia.     

YM022, a highly potent and selective CCKB antagonist inhibiting gastric acid secretion in the rat, the cat and isolated rabbit glands

Summary— We investigated the effects of the novel CCK_B/gastrin antagonist YM022 on gastric acid secretion in vivo and in vitro, compared to CI-988 and L365.260 as reference antagonists. In the anaesthetized rat, pentagastrin-induced stimulation of gastric acid secretion was dose-dependently and up to 100% inhibited by iv administration of YM022 with an ID₅₀ of 0.009 ± 0.0006 μmol/kg h in comparison to 0.6 ± 0.03 and 3.40 ± 0.05 μmol/kg h for CI-988 and L-365,260, respectively. In the gastric fistula cat, iv administration of YM022 produced a similar inhibitory effect with an ID₅₀ of 0.02 μmol/kg in comparison to 1.6 and 2.5 μmol/kg for CI-988 and L-365,260, respectively. Furthermore, bolus injection of 0.6 μmol/kg YM022 produced 100% inhibition within 30 min and 85% inhibition was still observed after 3 h. In the isolated rabbit gastric glands, CCK₈-stimulated ¹⁴C-aminopyrine uptake was inhibited according to the following rank order of potency: YM022 (IC₅₀ = 0.0012 μM) ≫ CI-988 (IC₅₀ = 0.2 μM) ≫ L365.260 (IC₅₀ = 2.8 μM). Unlike with L365.260, no influence of CI-988 and YM022 on histamine-stimulated acid output was shown in this study. Thus, YM022 is a highly potent and selective gastric CCK₈/gastrin receptor antagonist and has a long-lasting inhibitory effect on gastric acid secretion.     

Adenosine reduces airway excitatory non-cholinergic (e-NC) contraction through both A1 and A2 adenosine receptor activation in the guinea pig

Summary— The influence of adenosine and selective A₁ and A₂ agonists and antagonists was investigated on the cholinergic and the excitatory non-cholinergic (e-NC) contractions induced by electrical field stimulation in the guinea-pig bronchi. Adenosine (10 nM-1 mM) induced a concentration-dependent inhibition of the e-NC contraction (EC₅₀ = 90 ± 14 μM), whereas the cholinergic peak was only slightly affected. Preincubation of the tissue with the adenosine uptake blocker dipyridamole (10 μM) significantly shifted the concentration-inhibition curve to adenosine to the left (EC₅₀ = 10 ± 1 μM), suggesting an interaction with extracellular adenosine receptors of A₁ and/or A₂ subtype. To characterize the receptor type involved in this effect, selective adenosine derivatives were studied. The agonist to both A₁ and A₂ adenosine receptors, 5′-N-ethylcarboxamidoadenosine (NECA) was more potent than the selective A₁ agonist, (-)-R-6-phenylisopropyladenosine (R-PIA), in inhibiting the e-NC contraction (EC₅₀ = 0.10 ± 0.04 and 0.60 ±0.12 μM, respectively, with a maximal inhibition of 70 and 45%, respectively). The concentration-response curve to NECA was shifted to the right by the A₂ receptor selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (10 μM) (EC₅₀ = 1.4 ± 0.5 μ) as well as by the specific A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (10 μM) (EC₅₀ = 0.7 ± 0.3 μM). The inhibitory effect induced by the association of both antagonists, DPCPX and DMPX, was considerably potentiated (EC₅₀ > 22 ± 2.5 μM). The effect of R-PIA was also shifted to the right by DPCPX (EC₅₀ = 8.2 ± 1.6 μM) but was not modified by DMPX. The contractile response to exogenous substance P was unaffected by NECA pretreatment (0.3 μM). Altogether, these results suggest that adenosine-induced inhibition of e-NC contraction of guinea-pig bronchi is mediated through activation of both A₁ and A₂ adenosine receptors linked to inhibition of the release of neuropeptides from C-fibre nerve endings.     

Radioimmunoassay of Prostaglandins Fα, E1 and E2 in Human Plasma

Abstract. Antibodies against prostaglandins (PG)F₂α, E₁ and E₂ were obtained in rabbits immunized with respectively PG F₂α, PG E₁ and PG E₂ conjugated to bovine serum albumin by carbodiimide. A radioimmunoassay capable of measuring 7 pg of PG Fα, 2 pg of PG E₂ and 14 pg of PG Ej in human peripheral plasma is described. Plasma samples (pH 3, citric acid) are extracted with cyclohexane: ethyl acetate, 1:1 and then chromatographed on silicic acid columns to separate the prostaglandins into three fractions: fraction I, PG A, PG B and some unknown immunoraactive compounds; fraction II, PG E and fraction III PG Fα. The recovery is 80 %± 6. 2. Mean plasma levels iu adults of PG Fa and PG E, expressed in pg/ml: -PG Fα 12 ± 2. 8 (n = 25 men), 8 ± 2. 3 (n = 18 women, follicular phase), 7 ± 1. 4 (n = 18 women, luteal phase). -PG E₁ 40. 5 + 7. 6 (n = 13 men), 38 + 17. 1 (n = 10 women). -PG E₂ 4. 5 ± 1 (n = 12 adult subjects).
The major characteristics of the method described herein are the following: - a large volume of plasma has to be processed (10 ml or more for PG Fa and PG E₁, 5 ml or more for PG E₂). - a chromatographic step is necessary to separate the different prostaglandins which makes it possible to circumvent problems of immunological cross reactivity and interference with unknown immunoreactive compounds. - great care has been taken in collection of blood samples, especially to insure complete removal of blood cells namely platelets.     

Blockers of NMDA-operated channels decrease glutamate and aspartate extracellular accumulation in striatum during forebrain ischaemia in rats

Summary— Brain microdialysis was used to study changes in the glutamate and aspartate extracellular concentrations in the striatum of conscious rats submitted to 30 minutes cerebral ischaemia, using the four-vessel occlusion model. Perfusion of the N-methyl-D-aspartate (NMDA) receptor channel blockers, dizocilpine (MK-801; 75 μM) and Mg²⁺ (2.5 mM), inhibited the ischaemia-induced accumulation of glutamate and aspartate. The AMPA/kainate receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamylbenzo (F) quinoxaline (NBQX; 15 μM and 450 μM) had no effect on glutamate and aspartate levels during ischaemia. On the other hand, omission of Ca²⁺ from the perfusing solution did not alter the increases in glutamate and aspartate induced by ischaemia. These results suggest that the glutamate and aspartate accumulation in four-vessel occlusion ischaemia is mediated by activation of NMDA receptors in a Ca²⁺ independent manner.