Pregnancy protects against antiangiogenic and fibrogenic effects of angiotensin II in rat hearts.

AIM: To investigate the difference between physiological and pathological cardiac remodelling induced, respectively, by pregnancy and angiotensin (Ang) II, and to test the hypothesis that pregnancy protects against Ang II effects. METHODS: Female Wistar rats, pregnant (n = 12) and non-pregnant (n = 12), were implanted with mini-pumps containing saline (sham) or 150 ng kg(-1) min(-1) Ang II. Ten days later echocardiography and blood pressure measurement were performed. Expression of 22 genes was assessed using RT-PCR. Microscopic sections of LV were prepared to determine collagen content (Sirius Red staining), vessel density (ß-actin immunolabelling) and myocytes diameter (Toluidine Blue). RESULTS: Heart weight (HW) was increased in Ang II treated groups compared with their controls. Furthermore, HW of Ang II treated pregnant rats (1.0 ± 0.03 g) was higher than that in non-pregnant sham (0.7 ± 0.02 g), pregnant (0.8 ± 0.01 g) and Ang II treated non-pregnant (0.8 ± 0.02 g) rats. Relative LV wall thickness showed similar pattern. Aortic pressure was significantly increased in Ang II groups. Collagen content was increased in Ang II (4.0 ± 0.5%) compared with sham (1.5 ± 0.1%) but reduced again when treated rats were pregnant (2.8 ± 0.4%). Vessel density was reduced by 47.8% after Ang II treatment in non-pregnant and by only 13.9% in pregnant rats. Gene expression analysis showed increased expression of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), anykrin repeat domain-containing protein 1 (Ankrd-1), protein kinase C-α and -δ and tumour suppressor gene TP53 (p53) in Ang II treated groups and upregulation of ANF, BNP and Ankrd-1 remained when pregnancy was combined with Ang II. Pregnancy reduced expression of: α-myosin heavy chain, tumour necrosis factor-α, p53, endothelial nitric oxide synthase and inducible nitric oxide synthase. CONCLUSION: Pregnancy seems to counteract the detrimental effects of Ang II on fibrosis and angiogenesis in heart. In addition, pregnancy and Ang II lead to partly opposite changes in the expression of some genes important for heart function.

Gene expression, function and ischemia tolerance in male and female rat hearts after sub-toxic levels of angiotensin II.

To examine the response to chronic high-dose angiotensin II (Ang II) and a proposed milder response in female hearts with respect to gene expression and ischemic injury. Female and male litter-matched rats were treated with 400 ng kg(-1) min(-1) Ang II for 14 days. Hearts were isolated, subjected to 30-min ischemia and 30-min reperfusion in combination with functional monitoring and thereafter harvested for gene expression, WB and histology. Ang II-treated hearts showed signs of non-hypertrophic remodeling and had significantly higher end diastolic pressure after reperfusion, but no significant gender difference was detected. Ang II increased expression of genes related to heart function (ANF, ß-MCH, Ankrd-1, PKC-α, PKC-δ TNF-α); fibrosis (Col I-α1, Col III-α1, Fn-1, Timp1) and apoptosis (P53, Casp-3) without changing heart weight but with 68% increase in collagen content. High (sub-toxic) dose of Ang II resulted in marked heart remodeling and diastolic dysfunction after ischemia without significant myocyte hypertrophy or ventricular chamber dilatation. Although there were some gender-dependent differences in gene expression, female gender did not protect against the overall response.

Heptanol triggers cardioprotection via mitochondrial mechanisms and mitochondrial potassium channel opening in rat hearts.

AIM: To investigate mechanisms behind heptanol (Hp)-induced infarct size reduction and in particular if protection by pre-treatment with Hp is triggered through mitochondrial mechanisms. METHODS: Langendorff perfused rat hearts, isolated mitochondria and isolated myocytes were used. Infarct size, mitochondrial respiration, time to mitochondrial permeability transition pore (MPTP) opening and AKT and glycogen synthase kinase 3 beta (GSK-3ß) phosphorylation were examined. RESULTS: Pre-treatment with Hp reduced infarct size from 29.7 ± 3.4% to 12.6 ± 2.1%. Mitochondrial potassium channel blockers 5-hydroxy decanoic acid (5HD) blocking mitoK(ATP) and paxilline (PAX) blocking mitoK(Ca) abolished cardioprotective effect of Hp (Hp + 5HD 36.7 ± 2.9% and Hp + PAX 40.2 ± 2.8%). Hp significantly reduced respiratory control ratio in both subsarcolemmal and interfibrillar mitochondria in a dose-dependent manner (0.5-5.0 mm). The ADP oxygen ratio was also significantly reduced by Hp (2 mm). Laser scanning confocal microscopy of tetramethylrhodamine-loaded isolated rat myocytes using line scan mode showed that Hp increased time to MPTP opening. Western blot analysis showed that pre-treatment with Hp increased phosphorylation of AKT and GSK-3ß before ischaemia and after 30 min of global ischaemia. CONCLUSION: Pre-treatment with Hp protects the heart against ischaemia-reperfusion injury. This protection is most likely mediated via mitochondrial mechanisms which initiate a signalling cascade that converges on inhibition of opening of MPTP.

Pretreatment with insulin before ischaemia reduces infarct size in Langendorff-perfused rat hearts.

AIM: To compare the possible role of Akt and mammalian target of rapamycin (mTOR) in mediating cardioprotection against ischaemia under three different conditions: (1) During ischaemic preconditioning (IPC), (2) when insulin was given as a pretreatment agent (InsPC) and (3) when insulin was given as a reperfusion cell survival agent (Ins(R)). METHODS: Isolated perfused rat hearts were subjected to IPC (3 x 5 min) or InsPC (50 mU mL(-1); 3 x 5 min), before 30 min of regional ischaemia followed by 120 min of reperfusion +/- 1L-6-hydroxymethyl-chiro-inositol-2-[(R)-2-O-methyl-3-O-octadecylcarbonate] (HIMO) (20 microm; Akt inhibitor) or rapamycin (1 nm; mTOR inhibitor). In addition, insulin (3 mU mL(-1)) was given at the onset of reperfusion, +/- HIMO or rapamycin. Risk zone (R) and infarct size (I) were determined with Evans blue and tetrazolium staining respectively. Western blot analysis was performed on tissue from Langendorff-perfused rat hearts and cell lysates from cultured HL1 cells. RESULTS: IPC, InsPC and InsR treatment resulted in a significant reduction in infarct size compared to controls (all P < 0.05). This protective effect of IPC and insulin was abolished by the inhibitors. However, the putative Akt inhibitor, although capable of abolishing cardioprotection induced by insulin, was not able to inhibit insulin-induced phosphorylation of Akt in Langendorff-perfused rat hearts and cultured HL1 cells. The target for this compound therefore remains to be determined. CONCLUSION: IPC and insulin (either as InsPC or Ins(R)) appear to activate mTOR, and this kinase seems to play an essential role in cardioprotection against ischaemia and reperfusion injury as rapamycin blocked the protection.

Repeated simulated ischemia and protection against gap junctional uncoupling.

Ischemic preconditioning increases the heart's tolerance to a subsequent longer ischemic period. The aim of this study was to investigate the effect of early and delayed preconditioning on gap junction communication, connexin abundance, and phosphorylation in cultured neonatal rat cardiac myocytes. Prolonged ischemia followed 5 minutes after preconditioning in the early protocol, whereas 20 hours separated preconditioning and prolonged ischemia in the delayed preconditioning protocol. Gap junctional intercellular communication (GJIC) was assessed by Lucifer yellow dye transfer. An initial reduction in communication in response to sublethal ischemia was observed. This may be one mechanism whereby neighboring cells are protected from damaging substances produced during the first phase of subsequent regional ischemia in early preconditioning protocols. With respect to delayed preconditioning, the transient decrease in GJIC disappeared prior to prolonged ischemia, indicating that other mechanisms are responsible for delayed protection. Both early and delayed preconditioning preserved intercellular coupling after prolonged ischemia and this correlated with presence of less connexin43 dephosphorylation assessed by immunoblot.

Melatonin prevents cardioprotection induced by a multi-cycle ischaemic preconditioning protocol in the isolated perfused rat heart.

The powerful cardioprotective actions of melatonin, the chief secretory product of the pineal gland, have been attributed largely to its free radical-scavenging properties. Free radicals play an important role in the triggering action of ischaemic preconditioning, the phenomenon whereby exposure of the heart to one or more short episodes of ischaemia leads to protection against a subsequent long period of ischaemia. The aim of this study was, therefore, to establish whether melatonin, in view of its free radical-scavenging ability, would affect the beneficial actions of preconditioning. Isolated, perfused, working hearts were subjected to 1 x 5 minute or 3 x 5 min ischaemic preconditioning protocols, in the presence or absence of melatonin (50 microM), followed by 20 minutes global ischaemia and 30 minutes reperfusion. Use was also made of sodium nitroprusside (100 microM), a nitric oxide (NO) donor and preconditioning mimetic. Using functional recovery as the endpoint, melatonin abolished the cardioprotective effects of a multi-cycle (3 x 5 min) preconditioning protocol, while having no effect on a one-cycle (1 x 5 min) protocol or SNP (1 x 5 or 3 x 5 min) preconditioning. The results suggest that free radicals play an important role in the cardioprotection induced by a multi-cycle ischaemic preconditioning protocol and that this process could be attenuated by a potent scavenger such as melatonin.

Sustained anti-beta-adrenergic effect of melatonin in guinea pig heart papillary muscle.

OBJECTIVE: Anti-ss-adrenergic actions of several substances influence heart function significantly. The anti-ss-adrenergic effect of melatonin was investigated, with special attention to protein kinase C (PKC) and nitric oxide (NO). DESIGN: Guinea pig papillary muscles were exposed to melatonin (500 pM) for 15 min and 20 min washout. Contractile force was measured during a bolus of isoproterenol (300 nM) given before melatonin, at the end of melatonin-exposure and after washout. In separate experiments blockers of PKC, NO-synthase (NOS) and melatonin receptors were added, or forskolin (10 microM) substituted for isoproterenol. RESULTS: Melatonin significantly reduced the increase in contractile force in response to isoproterenol, both when present and after melatonin-washout. The reduction was unaffected by inhibition of PKC, while inhibition of melatonin receptors or NOS seemed to abolish the effect. Melatonin induced a sustained but not acute reduction of contractile force response with forskolin stimulation. This was abolished by NOS-inhibition. CONCLUSION: Receptor-mediated immediate and sustained anti-ss-adrenergic effects of melatonin were demonstrated in contractile function. A role for NO in the response was indicated, while a role for PKC was not verified.

Positive inotropic and sustained anti-beta-adrenergic effect of diadenosine pentaphosphate in human and guinea pig hearts. Role of dinucleotide receptors and adenosine receptors.

AIM: Diadenosine polyphosphates are present intracellularly and in extracellular fluid due to release from secretory vesicles in platelets, chromaffin cells and other cells. This study investigates effects of diadenosine pentaphosphate (AP5A) on heart muscle function. METHODS: Contractile force amplitude and action potential duration at 90% repolarization (APD90) were measured after challenge with AP5A 50 microm or isoproterenol 50-70 nM in guinea pig papillary muscles. Isoproterenol was given immediately after AP5A-exposure or after 45 min washout. AP5A was combined with antagonists to the purinergic P2 receptor (suramin 100 microm), the dinucleotide receptor [diinosine pentaphosphate 30 microm (IP5I)] or adenosine receptors [8-(P-sulfophenyl) theophylline 50 microm (8-SPT)]. RESULTS: Results are %-change (mean +/- SEM) from value before exposure. AP5A increased contractile force by 22 +/- 3%* (*P <0.05), and IP5I abolished this. AP5A prolonged APD90 by 7 +/- 2%*. AP5A significantly reduced response to isoproterenol acutely from 31 +/- 4* (controls) to 9 +/- 4% and after 45 min washout from 61 +/- 14* (controls) to 16 +/- 5%. 8-SPT abolished the sustained effect. Increase in contractile force by AP5A was confirmed in human atria trabecula preparations. CONCLUSION: AP5A increased contractile force and prolonged APD90. Contractile force increased by stimulation of the dinucleotide receptor in guinea pig myocardium. The sustained anti-beta-adrenergic effect of AP5A was due to adenosine receptor stimulation.

Adenosine induces prolonged anti-beta-adrenergic effects in guinea-pig papillary muscle.

A sustained anti-beta-adrenergic effect of adenosine has been reported. This study was initiated to investigate this topic and especially elucidate the role of protein kinase C (PKC). Contractile force amplitude and action potential duration at 90% repolarization (APD90) were measured in guinea-pig papillary muscles before and after 5 min challenge with 5 nm isoproterenol. Protocols contained 30 min exposure to the test agents adenosine 33 microm (ado), adenosine + PKC-inhibitor bisindolylmaleimide 20 nM (ado + BIM), PKC-activator 1,2-dioctanoyl-sn-glycerol 10 microm (DOG) and alpha-agonist phenylephrine 5 microm (phe). Isoproterenol was given at the end of test exposure and after 15 min washout. Results are mean +/- SEM of percentage-change, P < or = 0.05 considered significant and labelled *. The first isoproterenol challenge significantly increased contractile force (27 +/- 7%*) in the control group. Responses in the test groups were 2 +/- 4 (ado), 1 +/- 5 (ado + BIM), 14 +/- 4* (DOG), 0 +/- 2% (phe). After washout of adenosine, DOG and phenylephrine, isoproterenol induced 3 +/- 8 (ado), 23 +/- 5* (ado + BIM), 13 +/- 5* (DOG), 15 +/- 7% (phe) increase in test groups compared with 22 +/- 5%* increase in contractile force in the control group. After 45 min washout of adenosine the inotropic response was still significantly reduced compared with control (29 +/- 4 vs. 79 +/- 8%*). Isoproterenol stimulation shortened APD90 in controls at both time points (5 +/- 1%* and 4 +/- 1%*), with no significant shortening in test groups. Adenosine induces sustained anti-beta-adrenergic effects on contractile force as well as APD90. A role for PKC in signal transduction is supported with respect to contractile force.

The ischemic heart--experimental models.

Results obtained by experimental studies of the ischemic heart have been of tremendous importance for the understanding of physiology, biochemistry and lately also the molecular genetics of the heart. Experimental models in use for the study of the ischemic heart involve studies on the integrated organism, experiments with isolated hearts or multicellular preparation, and also studies of cells isolated from the heart. Regional ischemia in the anaesthetized animal has been a standard model. Knowledge about infarct size limitation as well as heart function in acute and chronic ischemia has been obtained based on experiments in a wide variety of species. The isolated perfused heart has been subjected to extensive use. As a result, the understanding of intracellular processes is constantly developing. Cell models and transgenic-mice models represent promising additions. Each model and each species has certain advantages and disadvantages. Variability in susceptibility towards ischemia and reperfusion is also present. The consequences of ischemia can be described as contractile dysfunction and stunning, arrhythmia and infarction each representing different endpoints of injury. The experimental model is also heavily dependent on the endpoint that is chosen for the study. Results obtained in one experimental model can, therefore, not be generalized into universal conclusions about the ischemic heart. With respect to the human and the disease caused by myocardial ischemia, fragments of knowledge put together from different types of experimental models create the background for successful design of potential treatment.

5-HD abolishes ischemic preconditioning independently of monophasic action potential duration in the heart.

OBJECTIVE: Blocking of the KATP channel with either glibenclamide or 5-hydroxydecanoate (5-HD) has been shown to abolish the infarct reducing effect of ischemic preconditioning (IPC) in hearts from several species, but the results in rat and rabbit have been equivocal. In this study we investigated if 5-HD could abolish IPC in rat and rabbit and further if IPC or IPC + 5-HD were affecting action potential duration in the rabbit heart. METHODS: The rat hearts were isolated and retrogradely perfused on a Langendorff perfusion apparatus with Krebs-Henseleit buffer. The rabbit experiments were performed in an in situ model. Rat and rabbit hearts were subjected to 30 min regional ischemia by ligating a coronary artery followed by 120 min (rat) or 150 min (rabbit) of reperfusion. The preconditioning protocol was one or three cycles of 5 min ischemia plus 5 min reperfusion in the rat and one cycle of 5 min ischemia plus 10 min reperfusion in the rabbit. In the rat 5-HD was added to the reservoir before ischemic preconditioning in different concentrations, and in the rabbit 5-HD was given as a bolus 5 mg/kg intraventricularly 2 min before the preconditioning ischemia. In the rabbit epicardial monophasic action potential duration at 50 % repolarization (MAPD50) was measured at 1, 2 and 5 min in each of the ischemic periods using a contact pressure electrode. Infarcts were measured with tetrazolium staining and risk zone volumes with fluorescent microspheres. RESULTS: All data are presented as infarct size in % of risk zone volume (mean +/- SEM). In the rat 200 microM of 5-HD abolished the protective effect of one cycle of IPC (28.6 +/- 4.7 versus 8.4 +/- 0.8) and 500M of 5-HD abolished three cycles of IPC (50.7 +/- 7.8 versus 8.4 +/- 2.0). Control was 40.9 +/- 2.8. In the rabbit 5-HD abolished IPC (41.2 +/- 7.2 versus 8.1 +/- 3.2). Control was 53.5 +/- 12.4. MAPD50 were significantly more shortened compared to control at 1 and 2 min into the 30 min ischemia for the IPC and IPC+5-HD. CONCLUSIONS: We conclude that 5-HD abolishes ischemic preconditioning when given before the preconditioning ischemia in both rat and rabbit but does not abolish the ischemia induced shortening of the action potential duration in the rabbit; thus, a role for the mitochondrial KATP channel and not the sarcolemmal KATP channel in the protective mechanism behind IPC is probable.

Coronary endothelium-derived vasodilation during cooling and rewarming of the in situ heart.

The integrity of coronary vascular endothelial vasodilator function during core cooling and rewarming was investigated in a pentobarbital-anesthetized open-chest dog model. Vasodilator response was assessed as the change from baseline blood flow by injecting the endothelial-dependent vasodilator acetylcholine (ACh) (1.0 microg) or the endothelial-independent vasodilator nitroglycerin (NTG) (50 microg) into the left anterior descending (LAD) coronary artery. Change in blood flow was measured using a transit time ultrasonic volume flowmeter technique. During cooling and rewarming LAD blood flow was significantly decreased. After rewarming, aortic pressure was artificially elevated to reach control. This procedure restored heart work (LV-RPP, left ventricular rate pressure product) and coronary perfusion pressure, but LAD blood flow remained lowered. Ability to dilate the vascular bed supplied by LAD, after injections of ACh or NTG, was present both during cooling and rewarming. At 25 degrees C coronary blood flow (LAD) increased from 3 +/- 1 to 9 +/- 1 mL x min(-1) in response to both ACh and NTG. Posthypothermic blood flow increased from 7 +/- 1 to 19 +/- 2 and 20 +/- 3 mL x min(-1) in response to ACh and NTG, respectively. Measured as the percent change from baseline LAD blood flow, the response was not significantly different from the one obtained in prehypothermic hearts. In conclusion, coronary vasodilator function, both endothelium dependent and endothelium independent, is present but not maintained at the same level during cooling to 25 degrees C and rewarming. In spite of the deterioration of cardiac function, no selective defect in the endothelium-dependent response was detected, either during hypothermia or after rewarming.

Ultrastructural alterations during the critical phase of reperfusion: a stereological study in buffer-perfused isolated rat hearts.

The present study focuses on myocardial ultrastructural alterations during the early phase of reperfusion. Isolated buffer-perfused rat hearts were exposed to standard perfusion (control group,n = 10); 60 min of global ischemia (n = 10); 60 min of global ischemia followed by 2 min of reperfusion (n = 10); or 60 min of global ischemia followed by 10 min of reperfusion (n = 10). The hearts were perfusion-fixed for electron microscopy, and ultrastructural evaluation was performed using stereological technique in order to obtain an estimate of the volume fraction and absolute volume of different tissue components. EFFECT OF ISCHEMIA: Neither the ventricular nor the myocytic volume differed significantly from the respective control values. Both the myocytic mitochondrial volume (135+/-8 vs control 89+/-6 microl) and the volume of myocytic clear space (35+/-6 vs control 10+/-2 microl) were significantly increased. The capillary volume (22+/-4 vs control 58+/-6 microl) and the volume of the capillary lumen (15+/-3 vs control 48+/-5 microl) were significantly decreased. The volume of the capillary wall, however, was not altered after exposure to ischemia (7+/-3 vs control 10+/-1 microl). ADDITIVE EFFECT OF ISCHEMIA AND REPERFUSION: Both the ventricular volume (755+/-28 vs control 600+/-32 microl) and the myocytic volume (396+/-24 vs control 287+/-16 microl) were significantly increased after 10 min of reperfusion. EFFECT OF REPERFUSION: The ischemic-induced myocytic mitochondrial swelling and increase of clear space were not reinforced during reperfusion. Furthermore, the volume of the capillary lumen and the capillary wall did not alter significantly in the groups exposed to reperfusion compared to the ischemic hearts. In conclusion, stereological evaluation did not reveal significant aggravation of ischemic-induced myocardial injury during the early phase of reperfusion.

The initial phase of myocardial reperfusion is not associated with aggravation of ischemic-induced ultrastructural alterations in isolated rat hearts exposed to prolonged global ischemia.

The present study focuses on the qualitative and sequential development of myocardial ultrastructural changes during the first 10 min of reperfusion in isolated rat hearts exposed to 60 min of global ischemia. The frequency of and the association between ultrastructural changes were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph the subcellular components of the myocytes (sarcolemma, mitochondria, myofilaments and nucleus) and the endothelial cells were evaluated and graded as slightly, moderately, or severely altered. Ischemia alone induced moderate to severe ultrastructural alterations. The myocytes revealed sarcolemmal disattachment or rupture. The myocytic mitochondria had a clear matrix with abundant broken cristae and amorphous matrix densities. The myofilamental pattern was irregular or even disrupted, and most nuclei had reduced density and showed margination of chromatin. The endothelium showed vacuolization, rupture of the plasma membrane, and extracellular accumulation of cellular debris. During the first 2 min of reperfusion severe ultrastructural alterations were partly reversed. After 10 min of reperfusion both the frequency and grade of myocardial ultrastructural alternations were similar to that observed after ischemia. Cristal adhesions occurred predominately during reperfusion and were associated with moderately and severely altered myocytic mitochondrial alterations. In conclusion, the results showed that ischemic-induced ultrastructural alterations were transiently improved upon reperfusion. With exception of the development of cristal adhesions, the acute phase of reperfusion was not associated with additional ultrastructural changes in isolated buffer-perfused rat hearts exposed to prolonged ischemia.

Left ventricular dysfunction following rewarming from experimental hypothermia.

This study was aimed at elucidating whether ventricular hypothermia-induced dysfunction persisting after rewarming the unsupported in situ dog heart could be characterized as a systolic, diastolic, or combined disturbance. Core temperature of 8 mongrel dogs was gradually lowered to 25 degreesC and returned to 37 degreesC over a period of 328 min. Systolic function was described by maximum rate of increase in left ventricular (LV) pressure (dP/dtmax), relative segment shortening (SS%), stroke volume (SV), and the load-independent contractility index, preload recruitable stroke work (PRSW). Diastolic function was described by the isovolumic relaxation constant (tau) and the LV wall stiffness constant (Kp). Compared with prehypothermic control, a significant decrease in LV functional variables was measured at 25 degreesC: dP/dtmax 2,180 +/- 158 vs. 760 +/- 78 mmHg/s, SS% 20.1 +/- 1.2 vs. 13.3 +/- 1.0%, SV 11.7 +/- 0.7 vs. 8.5 +/- 0.7 ml, PRSW 90.5 +/- 7.7 vs. 29.1 +/- 5.9 J/m. 10(-2), Kp 0.78 +/- 0.10 vs. 0.28 +/- 0.03 mm-1, and tau 78.5 +/- 3.7 vs. 25.8 +/- 1.6 ms. After rewarming, the significant depression of LV systolic variables observed at 25 degreesC persisted: dP/dtmax 1,241 +/- 108 mmHg/s, SS% 10.2 +/- 0.8 J, SV 7.3 +/- 0.4 ml, and PRSW 52.1 +/- 3.6 m. 10(-2), whereas the diastolic values of Kp and tau returned to control. Thus hypothermia induced a significant depression of both systolic and diastolic LV variables. After rewarming, diastolic LV function was restored, in contrast to the persistently depressed LV systolic function. These observations indicate that cooling induces more long-lasting effects on the excitation-contraction coupling and the actin-myosin interaction than on sarcoplasmic reticulum Ca2+ trapping dysfunction or interstitial fluid content, making posthypothermic LV dysfunction a systolic perturbation.

Equal reduction in infarct size by ethylisopropyl-amiloride pretreatment and ischemic preconditioning in the in situ rabbit heart.

UNLABELLED: Inhibition of Na+/H+ exchange with amiloride analogues has been shown to provide functional protection during ischemia and reperfusion and to reduce infarct size in isolated rat hearts. In rat hearts, treatment with ethylisopropyl-amiloride (EIPA, a selective Na+/H- exchange inhibitor) was additive to the protection afforded by ischemic preconditioning. In addition, such compounds have been demonstrated to reduce infarct size in in situ rabbit hearts. The aim of the present study was to determine to what extent preischemic treatment with EIPA could reduce infarct size in an in situ rabbit model of regional ischemia and reperfusion. We also wished to determine if this effect was additive to the infarct reducing effect of ischemic preconditioning. Anaesthetized, open chest rabbits, were subjected to 45 min of regional ischemia and 150 min of reperfusion. The risk zone was determined by fluorescent particles and infarct size was determined by TTC staining. Four groups were investigated: control, ischemic preconditioned (IP) (5 min of ischemia followed by 10 min reperfusion), EIPA (0.65 mg/kg iv given preischemically) and EIPA + IP. The main results expressed as percent infarction of the risk zone +/- S.E.M. for the different groups were: control 59.2+/-3.3% (n = 6), IP 16.3+/-2.1% (n = 6) (p < 0.001 vs. control), EIPA 16.9+/-4.1% (n = 5) (p < 0.001 vs. control), EIPA + IP 22.5 +/-9.5% (n = 6) (p < 0.001 vs. control). IN CONCLUSION: EIPA, when administered prior to ischemia, caused a reduction in infarct size in the in situ rabbit heart which was similar to that seen with ischemic preconditioning, however, the effect was not additive to ischemic preconditioning.