Protective effect of monoclonal antibodies against LFA-1 and ICAM-1 on myocardial reperfusion injury following global ischemia in rat hearts

The effects of anti-LFA-1 and anti-ICAM-1 monoclonal antibodies (MAbs) on the reperfusion injury of rat cardiac tissues after global ischemia were studied. Studies were performed using an isolated blood perfused heart preparation in which hearts were subjected to 30 min of global ischemia followed by 40 min of reperfusion. Isolated rat hearts were perfused with blood from an anesthetized support rat with or without anti-LFA-1 or anti-ICAM-1 monoclonal antibody administration (n = 10 in each group). Ventricular function, myocardial tissue water content and myocardial energy status were evaluated in this model. In the control group, ischemia and reperfusion of isolated hearts resulted in a 63.6 ± 2.7% recovery of left ventricular developed pressure (LVDP) and a 44 ± 7 % increase in coronary vascular resistance compared with pre-ischemic baseline values. Treatment with anti-LFA-1 MAb or anti-ICAM-1 MAb resulted in a 77.2 ± 1.5% and a 80.4 ± 3.0% recovery of LVDP, respectively. In addition, increase in coronary vascular resistance was only 23 ± 7% and 13 ± 6% in anti-LFA-1 and anti-ICAM-1-treated groups, respectively. Values are significantly different between the control group and MAb-treated groups. Ischemia and reperfusion resulted in a 16% increase of myocardial tissue water content (3.71 ± 0.03 in pre-ischemic baseline versus 4.29 ± 0.08 ml/g dry weight) in the control group, whereas that resulted in only 3.0 and 5.7 % increase in anti-LFA and anti-ICAM-1-treated groups, respectively. The difference between the control group and MAb-treated groups was significant. Cardiac energy status as assessed by adenosine triphosphate (ATP) concentration was markedly reduced in the control group at 40 min of reperfusion compared with pre-ischemic baseline values (5.70 ± 0.27 vs. 14.92 ± 0.48 μmol/g dry weight). In contrast, the reduction of myocardial ATP concentration at 40 min of reperfusion was significantly inhibited by anti-LFA-1 and anti-ICAM-1 monoclonal antibody treatment (5.70 ± 0.27 vs. 8.96 ± 0.52 and 8.10 ± 0.47 μmol/g dry weight, respectively). These results suggest that a LFA-1/ICAM-1 pathway plays a critical role in the pathogenesis of postischemic myocardial injury during early reperfusion period.     

Effects of the type-1 Na+/H+-exchange inhibitor cariporide (Hoe 642) on cardiac tissue

Ischemia leads to intracellular acidification which can be counteracted by the Na⁺/H⁺-exchange mechanism. A blockade of this exchanger has been hypothesized to cause stronger intracellular acidification in the course of ischemia thereby protecting the heart from ischemic damage. The aim of our study was to find out (1) whether in the course of ischemia areas become electrically silent, (2) whether this is enhanced by the Na⁺/H⁺-exchange inhibitor cariporide (4-Isopropyl-3-methylsulfonylbenzoyl-guanidine; Hoe 642) and whether cariporide has protective effects. Therefore, we submitted isolated rabbit hearts, perfused according to the Langendorff technique to regional ischemia (LAD occlusion) for 30 min followed by 30 min reperfusion with (n=7) or without (n=7) pre-treatment with 1 μM cariporide. Under these conditions 256-channel epicardial potential mapping was carried out. Under non-ischemic conditions cariporide did not alter any of the parameters under observation. We found that ischemia led to marked alterations of the activation pattern, to action potential shortening and a marked increase in the dispersion of refractoriness. In the ischemic region there was a significant ST deviation from the isoelectrical line (control 32±10; 30 min ischemia: 290±35 arbitrary units [a.u.]). This was markedly reduced by cariporide (control 39±10; 30 min ischemia: 170±25 a.u.). The increase in dispersion by ischemia (by 50±5 ms) was significantly counteracted by cariporide (increased dispersion by 20±4 ms). In a similar way the alteration of the activation pattern was antagonized. Under the influence of cariporide we found a lower increase in the left ventricular enddiastolic pressure, and a significantly slower recovery of the action potential duration. After 30 min of ischemia 24±5 (control series) 24.5±5 mm² (cariporide) became electrically silent. In a second series of experiments the incidence of arrhythmia was assessed: we found ventricular fibrillation in 6/7 untreated control hearts and in 4/7 cariporide treated hearts. In a third series of experiments we determined the intracellular [ATP] after 30 min of LAD occlusion using a histochemical method. We observed a decrease in [ATP] in the ischemic region as compared to the non-ischemic right ventricular wall, which was less pronounced in cariporide-treated hearts. Thus, we conclude that (1) cariporide protects the heart from ischemic damage and (2) at least under these conditions an enlargement of the electrically silent area did not occur. Received: 8 August 1997 / Accepted: 23 March 1998     

R 56865 exerts cardioprotective properties independent of the intracellular Na<Superscript>+</Superscript>-overload in the guinea pig heart

Reducing intracellular Na⁺-accumulation during ischemia exerts cardioprotective effects in reperfusion in a variety of models. Since slowly-inactivating Na⁺-channels may contribute to Na⁺-influx in ischemia, we investigated whether the ischemia-protective properties of R 56865, an inhibitor of slowly inactivating Na⁺-channels, are mediated by inhibition of the ischemic Na⁺-overload. Monitoring intracellular Na⁺ (Na⁺_i) by ²³Na-NMR-spectroscopy revealed a continuous rise of Na⁺_i during ischemia in the isolated perfused guinea pig heart. Within 30 and 60 min of ischemia, respectively, Na⁺_i had risen 2.6±0.2- and 4.4±0.2-fold compared to baseline (n=6). R 56865 (1 M) did not influence the time course of the Na⁺_i-accumulation at any point of the ischemic period. R 56865, however, showed marked cardioprotective properties: in the reperfusion period the agent markedly improved the restoration of left ventricular developed pressure (29.1±6.8 mm Hg vs. 2.4±2.0 mm Hg), ATP (2.8±0.3 mM vs. 1.7±0.6 mM) and phosphocreatine (10.9±2.2 mM vs. 6.8±1.1 mM), furthermore contracture development was reduced. The present study strongly suggests slowly-inactivating Na⁺-channels being at best a minor port of Na⁺-entry in the ischemic guinea pig heart. It clearly demonstrates that the potent cardioprotective properties of R 56865 are unrelated to intracellular sodium homeostasis.     

Comparison of the protective actions of Na+/H+ and Na+/Ca2+ exchange inhibitors in ischemic/reperfused rat hearts

The protective effects of the Na⁺/H⁺ exchange inhibitors amiloride, EIPA (5‐(N‐ethyl‐N‐isopropyl)‐amiloride), and HOE 694 (3‐methylsulfonyl‐4‐(1‐piperidino) benzoyl‐guanidine) and the Na⁺/Ca²⁺ exchange inhibitor, DCB (3,4‐Dichlorobenzamil) on ischemia (30 min) / reperfusion (30 min) injury were studied using Langendorff perfused rat hearts. EIPA and HOE 694 given before ischemia protected the heart during reperfusion from mechanical and metabolic disturbances. A weak protective effect was observed with amiloride, but not with DCB. The cardioprotective efficacies of these compounds correlated with their potencies as Na⁺/H⁺ exchange inhibitors as assessed by the NH₄Cl prepulse method. None of the inhibitors was effective when given at reperfusion. EIPA and HOE 694 decreased myocardial rigidity as assessed by the resting tension (RT) which elevated during reperfusion. EIPA led to a more marked attenuation of RT elevation during reperfusion rather than ischemia, whereas diltiazem, a Ca²⁺ channel blocker, suppressed RT elevation during ischemia but did not cause a further attenuation of RT during reperfusion. Treatment with EIPA as well as diltiazem before ischemia showed a direct negative chronotropic effect. Cardioprotective effects were also observed with diltiazem. These results suggest that Na⁺/H⁺ exchange plays a more important role in ischemia‐reperfusion‐induced myocardial injury than does Na⁺/Ca²⁺ exchange. The cardioprotective effects of EIPA appear to be produced by Ca²⁺ channel blockade during ischemia and by Na⁺/H⁺ exchange inhibition during reperfusion. Drug Dev. Res. 48:160–170, 1999. © 1999 Wiley‐Liss, Inc.     

Dose‐dependent effects of sildenafil on post‐ischaemic left ventricular function in the rat isolated heart

Objectives Sildenafil may be beneficial during myocardial ischaemia/reperfusion, but this effect may be dose‐dependent, accounting for previous conflicting results. We have explored the effects of two acute and one chronic administration regimen on left ventricular function. Methods The study was conducted on 36 Wistar rats (290 ± 7 g). Sildenafil was administered 30 min before ischaemia at a low (0.7 mg/kg, n= 8) or high (1.4 mg/kg, n= 8)dosage. The chronic treatment arm (n= 8) consisted of two daily injections of sildenafil (0.7 mg/kg) for three weeks. The control group was formed by 12 rats. Ischaemic contracture, post‐ischaemic recovery and hypercontracture were measured in isolated, Langendorff‐perfused preparations. Key findings Ischaemic contracture tended to be lower after high‐dose sildenafil, while remaining unchanged after low‐dose or chronic sildenafil administration. Compared with controls (62.9 ± 2.0% of baseline developed pressure), post‐ischaemic recovery was higher (P= 0.0069) after low dose (75.1 ± 2.4%), unchanged (P= 0.13) after high dose (69.1 ± 2.1%), but lower (P < 0.001) after chronic (42.9 ± 4.5%) sildenafil administration. Compared with controls (71.8 ± 3.9 mmHg), hypercontracture was higher (P= 0.0052) after chronic sildenafil administration (89.5 ± 4.1 mmHg), but similar after acute low dose (65.7 ± 3.3 mmHg, P= 0.33) or high dose (67.1 ± 4.7 mmHg, P= 0.43). Conclusions The effects of sildenafil after ischaemia/reperfusion were strongly dose‐dependent. Beneficial actions on left ventricular function were evident after acute pretreatment with a low dosage, but were lost after doubling the dose. Chronic sildenafil administration deteriorated left ventricular function during ischaemia and reperfusion.     

A NEW METHOD FOR COMBINED ISOMETRIC AND ISOBARIC PHARMACODYNAMIC STUDIES ON PORCINE CORONARY ARTERIES

1. The principal aim of the present study was to explore the isometric and isobaric capacity of a new intravascular technique, impedance planimetry, in basic pharmacodynamic investigations on porcine isolated epicardial coronary arteries. 2. The balloon-based catheter technique provides simultaneous measurements of luminal cross-sectional area and pressure. Sources of errors that may influence the accuracy of measurements were evaluated in detail. 3. Under isometric conditions, the stretch ratio-tension diagram showed typical developments of resting and active tensions of the smooth muscle when exposed to alternating maximal K⁺ depolarization and mechanical stretching. The mean (±SEM) maximum active tension was 28.43 ± 1.72 mN/mm, which was reached at a stretch ratio of 1.26 ±0.02, corresponding to a resting tension of 10.50±0.53 mN/mm (n= 7). The concentration-response relationship to K⁺ at optimal basal tension was characterized by a mean (±SEM) pD2 value of 1.67±0.01 (n= 7). 4. Under isobaric conditions in the pressure range 40-140 mmHg, the method allowed the investigation of active vascular responses to partial K depolarization. The maximal active response to 25 mmol/L K⁺ was found at the transmural pressure of 60 mmHg (n= 7). To obtain full K⁺ concentration-response curves, a basal tension corresponding to a transmural pressure of 120 mmHg was required. The mean (±SEM) pD₂ value for the concentration-response relationship to K⁺ was 1.53±0.01 (n= 10).     

Assessing the neurotoxic effects of palytoxin and ouabain,both Na+/K+-ATPase inhibitors,on the myelinated sciatic nerve fibres of the mouse: An ex vivo electrophysiological study

Palytoxin (PlTX) is a marine toxin originally isolated from the zoantharians of the genus Palythoa. It is considered to be one of the most lethal marine toxins that block the Na⁺/K⁺-ATPase. This study was designed to investigate the acute effects of PlTX and ouabain, also an Na⁺/K⁺-ATPase blocker, on the mammalian peripheral nervous system using an ex vivo electrophysiological preparation: the isolated mouse sciatic nerve. Amplitude of the evoked nerve compound action potential (nCAP) was used to measure the proper functioning of the sciatic nerve fibres. The half-vitality time of the nerve fibres (the time required to inhibit the nCAP to 50% of its initial value: IT₅₀) incubated in normal saline was 24.5 ± 0.40 h (n = 5). Nerves incubated continuously in 50.0, 10.0, 1.0, 0.5, 0.250 and 0.125 nM of PlTX had an IT₅₀ of 0.06 ± 0.00, 0.51 ± 0.00, 2.1 ± 0.10, 8.9 ± 0.30, 15.1 ± 0.30 h, and 19.5 ± 0.20 h, respectively (n = 5, 3, 4, 4, 10). PlTX was extremely toxic to the sciatic nerve fibres, with a minimum effective concentration (mEC) of 0.125 nM (n = 5) and inhibitory concentration to 50% (IC₅₀) of 0.32 ± 0.08 nM (incubation time 24 h). Ouabain was far less toxic, with a mEC of 250.0 μM (n = 5) and IC₅₀ of 370.0 ± 18.00 μM (incubation 24.5 h). Finally, when the two compounds were combined – e.g. pre-incubation of the nerve fibre in 250.0 μM ouabain for 1 h and then exposure to 1.0 nM PlTX – ouabain offered minor a neuroprotection of 9.1–17.6% against PlTX-induced neurotoxicity. Higher concentrations of ouabain (500.0 μM) offered no protection. The mouse sciatic nerve preparation is a simple and low-cost bioassay that can be used to assess and quantify the neurotoxic effects of standard PlTX or PlTX-like compounds, since it appears to have the same sensitivity as the haemolysis of erythrocytes assay – the standard ex vivo test for PlTX toxicity.     

The antiarrhythmic dipeptide ZP1609 (danegaptide) when given at reperfusion reduces myocardial infarct size in pigs

Connexin 43 is located in the cardiomyocyte sarcolemma and in the mitochondrial membrane. Sarcolemmal connexin 43 contributes to the spread of myocardial ischemia/reperfusion injury, whereas mitochondrial connexin 43 contributes to cardioprotection. We have now investigated the antiarrhythmic dipeptide ZP1609 (danegaptide), which is an analog of the connexin 43 targeting antiarrhythmic peptide rotigaptide (ZP123), in an established and clinically relevant experimental model of ischemia/reperfusion in pigs. Pigs were subjected to 60 min coronary occlusion and 3 h reperfusion. ZP1609 (n?=?10) was given 10 min prior to reperfusion (75 μg/kg b.w. bolus i.v. + 57 μg/kg/min i.v. infusion for 3 h). Immediate full reperfusion (IFR, n?=?9) served as control. Ischemic postconditioning (PoCo, n?=?9; 1 min LAD reocclusion after 1 min reperfusion; four repetitions) was used as a positive control of cardioprotection. Infarct size (TTC) was determined as the end point of cardioprotection. Systemic hemodynamics and regional myocardial blood flow during ischemia were not different between groups. PoCo and ZP1609 reduced infarct size vs. IFR (IFR, 46?±?4 % of area at risk; mean?±?SEM; PoCo, 31?±?4 %; ZP1609, 25?±?5 %; both p?<?0.05 vs. IFR; ANOVA). There were only few arrhythmias during reperfusion such that no antiarrhythmic action of ZP1609 was observed. ZP1609 when given before reperfusion reduces infarct size to a similar extent as ischemic postconditioning. Further studies are necessary to define the mechanism/action of ZP1609 on connexin 43 in cardiomyocytes.     

KR-31761, a Novel K+ATP-Channel Opener,Exerts Cardioprotective Effects by Opening Both Mitochondrial K+ATP and Sarcolemmal K+ATP Channels in Rat Models of Ischemia/Reperfusion-Induced Heart Injury

The cardioprotective effects of KR-31761, a newly synthesized K⁺_ATP opener, were evaluated in rat models of ischemia/reperfusion (I/R) heart injury. In isolated rat hearts subjected to 30-min global ischemia/30-min reperfusion, KR-31761 perfused prior to ischemia significantly increased both the left ventricular developed pressure (% of predrug LVDP: 17.8, 45.1, 54.2, and 62.6 for the control, 1 μM, 3 μM, and 10 μM, respectively) and double product (DP: heart rate × LVDP; % of predrug DP: 17.5, 44.9, 56.2, and 64.5 for the control, 1 μM, 3 μM, and 10 μM, respectively) at 30-min reperfusion while decreasing the left ventricular end-diastolic pressure (LVEDP). KR-31761 (10 μM) significantly increased the time to contracture during the ischemic period, whereas it concentration-dependently decreased the lactate dehydrogenase release during reperfusion. All these parameters were significantly reversed by 5-hydroxydecanoate (5-HD, 100 μM) and glyburide (1 μM), selective and nonselective blockers of the mitochondrial K⁺_ATP (mitoK⁺_ATP) channel and K⁺_ATP channel, respectively. In anesthetized rats subjected to 30-min occlusion of left anterior descending coronary artery/2.5-h reperfusion, KR-31761 administered 15 min before the onset of ischemia significantly decreased the infarct size (72.2%, 55.1%, and 47.1% for the control, 0.3 mg/kg, i.v., and 1.0 mg/kg, i.v., respectively); and these effects were completely and almost completely abolished by 5-HD (10 mg/kg, i.v.) and HMR-1098, a selective blocker of sarcolemmal K⁺_ATP (sarcK⁺_ATP) channel (6 mg/kg, i.v.) administered 5 min prior to KR-31761 (72.3% and 67.9%, respectively). KR-31761 only slightly relaxed methoxamine-precontracted rat aorta (IC₅₀: >30.0 μM). These results suggest that KR-31761 exerts potent cardioprotective effects through the opening of both mitoK⁺_ATP and sarcK⁺_ATP channels in rat hearts with a minimal vasorelaxant effect.     

Urate and antioxidants inhibit Na+-adenosine transport in rat renal brush border membranes

The effects of urate and antioxidants were evaluated on sodium-dependent [³H]adenosine transport (Na⁺/ADO) in rat renal brush border membrane vesicles (BBMV). Na⁺/ADO was estimated for a range of adenosine concentrations of 1–10 μmol/l in BBMV preincubated with urate (0.5–50 μmol/l). Michaelis-Menten kinetics showed a significant increase in K_m values from 2.48±0.49 μmol/l in control to 20.58±4.56 μmol/l with 50 μmol/l urate; V_max (243±15 pmol/mg protein×min) was not modified. Menadione (10 μmol/l) significantly increased the Na⁺/ADO activity, from 17.57±5.50 in the control, to 27.70±7.60 pmol/mg prot.×min (a 1.60 times increase, p<0.05). This stimulation was prevented when BBMV were preincubated with either 1 μmol/l α-tocopherol (trolox) or urate. Similarly conjugated dienes and malonaldehyde were stimulated in a dose-dependent fashion by menadione and the effect was inhibited with 10 μmol/l trolox. The antioxidants probucol, captopril and allopurinol inhibited in a concentration-dependent manner the Na⁺/ADO (IC₅₀ were 79±8, 100±9 and 89±9 nM, respectively). This effect might be specific on K_m of the Na⁺/ADO, since 1 μmol/l trolox (IC₅₀=1000±20 nM), inhibited V_max but not K_m of the Na⁺/glucose transport. Our results suggest that the Na⁺/ADO in BBMV is modified by agents that affect the redox status of the membranes.     

Protection of the right ventricle from ischemia and reperfusion by preceding hypoxia

We have previously shown that 2 weeks of hypoxia protect the right ventricle of the rat heart from subsequent ischemia and reperfusion (I/R). In the present study, we examined the following: (1) Do shorter periods of hypoxia protect from subsequent I/R? (2) Does intermittent normoxia increase the cardioprotective effect? (3) Is hypoxia-inducible factor-1α (HIF-1α), erythropoietin (EPO), or vascular endothelial growth factor (VEGF) involved in the protective effects? Preischemic cardiac work was followed by global ischemia, reperfusion, and postischemic cardiac work (15 min each). External heart work was determined at the end of both work phases. Four groups of hearts were investigated: hearts from normoxic rats (n?=?8), hearts from rats after 24 h of continuous hypoxia (10.5% inspired oxygen, n?=?7), hearts from rats after 24 h hypoxia with a single intermission of 30 min normoxia (n?=?9), and hearts from rats after 24 h hypoxia and multiple intermissions of 30 min normoxia (n?=?7). Protein levels of HIF-1α and mRNA levels of EPO and VEGF were determined in right ventricular tissue of normoxic and hypoxic hearts. Postischemic right heart recovery was better in all three hypoxic groups compared with normoxic hearts (61.8?±?5.9%, 65.6?±?3.0%, and 75.7?±?2.6% vs. 46.0?±?3.9%, p?p?p?=?0.02). No differences in EPO and VEGF mRNA levels were found between normoxic and hypoxic hearts. Twenty-four hours of continuous hypoxia protect the isolated working right heart from subsequent ischemia and reperfusion. When preceding hypoxia is interrupted by multiple reoxygenation periods, there is a further significant increase in cardiac functional recovery. HIF-1α may be involved in the protective effect.     

Na+ channel modulation and force-frequency relationship in human myocardium

The enhancement of force of contraction (FOC) following increasing frequencies of stimulation is an important mechanism of positive inotropy in human myocardium. The present study aimed to investigate the influence of alterations in Na⁺ influx on FFR in human myocardium. Isometric FOC of electrically stimulated right auricular trabeculae (AUT, n=12) from human nonfailing hearts (n=8) was measured at different stimulation rates (0.5-3 Hz) under control conditions, after increasing Na⁺ influx by the addition of (±)BDF 9148 (BDF, 3 μmol l^-1) and after decreasing Na⁺ influx by the addition of lidocaine (LIDO, 10 μmol l^-1). Additionally, the rate dependent changes in diastolic tension (DT) were measured in all experiments. Under control conditions FOC increased with increasing frequencies of stimulation. The rate at which maximal FOC was observed (SFmax) was 2.0±0.2 Hz and maximal increase in FOC (PIEmax) by increasing frequency of stimulation was +1.5±0.5 mN. After increase of Na⁺ influx by BDF (3 μmol l^-1) SFmax was decreased to 0.8±0.1 Hz (p<0.05 versus control) and PIEmax was +0.1±0.3 mN (p<0.05). When Na⁺ influx was diminished by LIDO (10 μmol l^-1) SFmax and PIEmax were increased compared to control (2.4±0.1 Hz and +4.1±0.9 mN, p<0.05 versus control). The diastolic tension (DT) of AUT at 3 Hz was not changed at higher rates in the control group and after application of LIDO (10 μmol l^-1), whereas after enhancement of Na⁺ influx by BDF there was an increase in DT of +0.7±0.2 at 3Hz (p<0.05 versus control and LIDO). An enhanced Na⁺ influx leads to a decrease in the optimal frequency and to a smaller force potentiation by higher stimulation rates which could be at least partly due to incomplete relaxation at higher frequencies, whereas a reduced Na⁺ influx is followed by opposite alterations. It is concluded that besides Ca²⁺ handling also Na⁺ influx and Na⁺ homeostasis might determine the frequency-induced force potentiation in human myocardium. Thus, the negative FFR in diseased human myocardium might result from changes in cellular Ca²⁺ or Na⁺ regulatory sites. Received: 20 November 1996 / Accepted: 21 February 1997     

Axonal protection achieved by blockade of sodium/calcium exchange in a new model of ischemia in vivo

Ischemic white matter injury has been relatively little studied despite its importance to the outcome of stroke. To aid such research a new rat model has been developed in vivo and used to assess whether blockade of the sodium/calcium exchanger is effective in protecting central axons from ischemic injury. Vasoconstrictive agent endothelin-1 was injected into the rat spinal cord to induce ischemia. KB-R7943 or SEA0400 was administered systemically to block the operation of the sodium/calcium exchanger. Endothelin-1 caused profound reduction of local blood perfusion and resulted in a prompt loss of axonal conduction. Whereas recovery of conduction following vehicle administration was only to 10.5 ± 9% of baseline (n = 8) 4.5 h after endothelin-1 injection, recovery following KB-R7943 (30 mg/kg, i.a.) administration was increased to 35 ± 9% of baseline (n = 6; P < 0.001). SEA0400 (30 mg/kg, i.a.) was also protective (33.2 ± 6% of baseline, n = 4; P < 0.001). Neither drug improved conduction by diminishing the severity of the ischemia. The protective effect of KB-R7943 persisted for at least 3 days after ischemia, as it improved axonal conduction (76.3 ± 11% for KB-R7943 vs. 51.0 ± 19% for vehicle; P < 0.01) and reduced lesion area (55.6 ± 15% for KB-R7943 vs. 77.9 ± 9% for vehicle; P < 0.01) at this time. In conclusion, a new model of white matter ischemia has been introduced suitable for both structural and functional studies in vivo. Blocking the sodium/calcium exchanger protects central axons from ischemic injury in vivo.     

Long-term nifedipine treatment reduces calcium overload in isolated reperfused hearts of diabetic rats

• 1.1. Streptozotocin-induced diabetic rats showed poor post-ischemic recovery in isolated working rat hearts.
• 2.2. Diabetic rats showed myocardial Na⁺ accumulation after ischemia, and Ca²⁺ level and water content elevation after reperfusion.
• 3.3. A 6-wk nifedipine treatment improved post-ischemic recovery of cardiac parameters and prevented myocardial Na⁺ accumulation after ischemia and myocardial Ca²⁺ level and water content elevation after reperfusion of diabetic rats.
• 4.4. Results suggest that nifedipine treatment improves cardiac dysfunction in the reperfused ischemic hearts of diabetic rats through normalization of the Na⁺-Ca²⁺ imbalance and water content.

     

The erythrocyte-perfused “working heart” model: Hemodynamic and metabolic performance in comparison to crystalloid perfused hearts

A brief period of ischemia was used to evaluate an erythrocyte-enriched Krebs-Henseleit (KH) buffer (n=8) compared to KH only (n=8) in an isolated working rabbit heart. Experimental protocol was as follows: preischemic baseline, 5 min of global ischemia followed by 45 min of reperfusion. Preischemic heart rate was identical, coronary flow was significantly lower (2.7 versus 5.6 mL/min/g wet wt, p<0.01), the other hemodynamic and biochemical values were significantly higher in erythrocyte-perfused hearts: aortic flow 23.5 versus 12.0, p<0.01; cardiac output 26.2 versus 17.6, p<0.01; all in mL/min/g wet wt; dp/dt max 1286 versus 997 mmHg/s, p<0.01; myocardial oxygen consumption 3.5 versus 2.3 μmol/min/g wet wt, p<0.05. During early reperfusion, in the erythrocyte-perfused hearts, coronary flow further increased (p<0.003), the other hemodynamic parameters returned to baseline values in both groups. High-energy phosphates showed significantly higher values (ATP 2.0±0.1 versus 1.3±0.1, p<0.05; CrP 2.0±0.2 versus 1.6±0.1, p<0.05 all in μmol/g wct wt), water content was significantly lower (81% versus 74%, p<0.05) in erythrocyte-perfused hearts. It can be concluded that the erythrocyte-perfused working heart model provides excellent oxygenation, leading to superior hemodynamic and metabolic performance. Additionally, in the erythrocyte-perfused hearts preservation of coronary flow reserve underlines the physiological competency of this prepar-ation.     

Thaliporphine protects ischemic and ischemic‐reperfused rat hearts via an NO‐dependent mechanism

In ischemia or ischemia‐reperfusion (I/R), nitric oxide (NO) can potentially exert several beneficial effects. Thaliporphine, a natural alkaloid with Ca²⁺ channel‐activating and Na⁺/K⁺ channel‐blocking activities, increased NO levels and exerted cardioprotective action in ischemic or I/R rats. The role of NO in the cardioprotective actions of thaliporphine was assessed. The severity of rhythm disturbances and mortality in anesthetized rats with either coronary artery occlusion for 30 min, or 5 min followed by 30‐min reperfusion, were monitored and compared in thaliporphine‐ vs. placebo‐treated groups. Thaliporphine treatment significantly increased NO and decreased lactate dehydrogenase (LDH) levels in the blood during the end period of ischemia or I/R. These changes in NO and LDH levels by thaliporphine were associated with a reduction in the incidence and duration of ventricular tachycardia (VT) and ventricular fibrillation (VF) during ischemic or I/R period. The mortality of animals was also completely prevented by 1 × 10^–8 moles/kg of thaliporphine. In animals subjected to 4 h of left coronary artery occlusion, 1 × 10^–7 moles/kg of thaliporphine dramatic reduced cardiac infarct zone from 46 ± 6% to 7.1 ± 1.9%. Inhibition of NO synthesis with 3.7 × 10^–6 moles/kg of N^ω ‐nitro‐L‐arginine methyl ester (L‐NAME) abolished the beneficial effects of thaliporphine during 30 min or 4 h myocardial ischemia. However, the antiarrhythmic activity and mortality reduction efficacy of thaliporphine during reperfusion after 5 min of ischemia was only partially antagonized by L‐NAME. These results showed that thaliporphine efficiently exerted the cardioprotections either in acute or prolonged coronary artery occlusion or occlusion‐reperfusion situations. The fact that thaliporphine induced cardioprotective effects were abrogated by L‐NAME indicates that NO is an important mediator for the cardioprotective effects of thaliporphine in acute or prolonged ischemia, whereas antioxidant activities may contribute to the protection of I/R injury. Drug Dev. Res. 52:446–453, 2001. © 2001 Wiley‐Liss, Inc.     

Cardiovascular actions of nitric oxide synthase inhibition in the portal hypertensive rat

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Direct inhibition by taurine of the ATP-sensitive K+ channel in guinea pig ventricular cardiomyocytes

• 1.1. Effects of taurine on the ATP-sensitive K⁺ channel in isolated guinea pig ventricular cardiomyocytes were examined using an inside-out patch voltage-clamp mode. All experiments were performed at 36°C.
• 2.2. The ATP-sensitive K⁺ channel was activated outwardly. ATP-free and 140 mM K⁺ solution in the bath and 140 mM K⁺ in the pipette solution were used. The amplitude was 2.2 ± 0.3 pA (n=9) at + 50 mV. The channel conductance was 31 ± 3 pS (n=9). Glibenclamide (1 μM) blocked the channel opening.
• 3.3. Taurine decreased the open probability (as a mean patch current for 30 sec) of the channel by 21.5 ± 2.4% (n = 8, P< 0.01) at 10 mM, and almost blocked it (n = 8, P< 0.001) at 20 mM.
• 4.4. Taurine did not affect the channel conductance; these responses were reversible.
• 5.5. These results suggest that taurine directly modulates the open probability of the ATP-sensitive K⁺ channel, resulting in regulation of the cell functions.

     

The effect of allopurinol on Na+K+ATPase related lipid peroxidation in ischemic and reperfused rabbit kidney

1. Na⁺K⁺ATPase is a membrane bound enzyme whose activity is essential for maintenance of cell viability. Lipid peroxidation changes membrane fluidity and enzyme activity.2. The purpose of this study was to investigate the effect of allopurinol (free radical scavenger) on Na⁺K⁺ATPase activity in rabbit kidney cortex membrane. In this in vivo study we created ischemia and reperfusion in rabbit kidneys.3. Enzyme activity were low in ischemic and reperfused kidneys, compared to the controls. In allopurinol treated ischemic and reperfused groups, the levels of Na⁺K⁺ATPase activity were high compared to the untreated group.4. It has been concluded that allopurinol may protect this enzyme activity.