Biomedical subjects

M Karmazyn

Publications and source records attributed to M Karmazyn.

At least 19 recordsLinked to original sources

PubMed1992

Protective effects of amiloride on the ischemic reperfused rat heart. Relation to mitochondrial function.

We examined the effect of amiloride on mechanical, electrical and mitochondrial function as well as ultrastructural integrity, in isolated rat hearts subjected to 30 min low-flow ischemia and 30 min reperfusion. In control hearts, ischemia produced a rapid loss of contractility and a concomitant elevation in resting tension which were associated with a 100% incidence in arrhythmic activity. Reperfusion produced a 22 and 54% recovery in force and rate of force (dF/dt) development, respectively. In control hearts the incidence of arrhythmias was 100% within 5 min of reperfusion which then declined to 50% by 30 min. Ultrastructural defects in these hearts were restricted primarily to mitochondrial damage. Amiloride significantly attenuated the elevation in resting tension at the end of ischemia. Postischemic recovery was significantly increased to 38 and 86% for force and dF/dt, respectively and the incidence of arrhythmias was reduced to 30%. No ultrastructural defects were ever observed in amiloride-treated reperfused hearts. Both interfibrillar and subsarcolemmal mitochondria exhibited depressed respiratory function and adenine nucleotide translocase activity. Although virtually all parameters tended to be elevated in mitochondria isolated from amiloride-treated hearts, a significant increase was seen in only one case. Our results therefore demonstrate an ability of amiloride to enhance postischemic contractile recovery and reduce the incidence of arrhythmias, particularly during reperfusion, an effect associated with virtual total prevention of ultrastructural defects. Although the salutary effect was not significantly correlated to improved mitochondrial function, this dissociation may have been due to removal of damaged mitochondria during the isolation process, in view of diminished mitochondrial damage as viewed by transmission electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗

PubMed1992

Adenosine A1 receptor activation attenuates cardiac injury produced by hydrogen peroxide.

Adenosine has been shown to protect the ischemic and reperfused myocardium. To examine whether the protective effect of the nucleoside is mediated by modulation of oxidative stress, isolated rat hearts were perfused for 30 minutes with 100 microM H2O2 or an exogenous free radical-generating system consisting of purine (3.06 mM) and xanthine oxidase (10 units/l) in the presence or absence of drugs acting on adenosine A1 or A2 receptors. H2O2 alone produced a greater than 90% loss in contractility concomitant with a threefold elevation in resting tension, although these effects occurred in the absence of ultrastructural damage. Two A1 receptor agonists N6-cyclopentyladenosine (CPA, 1 microM) and R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA, 1 microM) significantly attenuated the cardiodepressant effects of H2O2 and depressed the elevation in resting tension; however, only the effect of CPA was found to be significant with regard to the latter parameter. A similar concentration of S(+)-N6-(2-phenylisopropyl)adenosine (S-PIA), a markedly less potent A1 receptor agonist, was found to be without beneficial effect. However, a significant protective effect against both the reduction in contractility and the elevation in resting tension was seen with a 10-fold elevation in the concentration of S-PIA (10 microM). The protective effects on functional parameters were associated with preservation of high-energy phosphate and adenine nucleotide contents after 30 minutes of H2O2 treatment. The salutary effects of all drugs were reversed in the presence of the A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (0.5 microM). An A2 receptor agonist 2-[p-(carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine, termed CGS 21680 (1 microM), failed to alter the cardiac response to H2O2 with regard to all parameters studied. Neither a 50% reduction in external CaCl2 concentration nor treatment with 10 microM DL-propranolol exerted salutary effects against H2O2-induced dysfunction. None of the A1 receptor agonists modulated the response to purine plus xanthine oxidase. Our results demonstrate a selective protective effect of adenosine A1 receptor activation against the cardiac toxicity of H2O2 and provide, at least in part, a basis for the cardioprotective actions of adenosine and its analogues.

Adenosine↗

PubMed1991

The 1990 Merck Frosst Award. Ischemic and reperfusion injury in the heart. Cellular mechanisms and pharmacological interventions.

Reperfusion in the heart represents an important form of tissue injury, particularly in view of the emerging importance of reperfusion protocols aimed at salvaging the ischemic myocardium. Both the manifestations and the causes of reperfusion injury are multifold. With respect to the former, reperfusion injury can be characterized by various abnormalities including development of arrhythmias, contractile dysfunction, ultrastructural damage as well as various defects in intracellular biochemical homeostasis. The mechanisms underlying myocardial reperfusion injury are equally complex, but most likely involve numerous processes acting in concert resulting in eventual cell death. In this review, a description of various such potential mechanisms, which represent primary interests of the author, are presented. An understanding of these mechanisms has led to novel pharmacological approaches towards the protection of the reperfused myocardium. For instance, several lines of evidence implicate enhanced eicosanoid, and in particular prostaglandin, synthesis in reperfusion injury, since (1) such injury is involved with enhanced prostaglandin biosynthesis, (2) inhibition of prostaglandin synthesis with various nonsteroidal anti-inflammatory drugs attenuates injury, and (3) exogenous prostaglandins increase injury. Another intracellular process that is emerging as an important contributor to reperfusion injury in the heart is the Na+/H+ exchanger, which is most likely activated upon reperfusion. Such activation would lead to numerous intracellular disturbances including the increased synthesis of prostaglandins and elevated intracellular Ca2+ concentrations. Indeed, inhibitors of Na+/H+ exchange such as amiloride have been shown to effectively inhibit reperfusion injury. Reperfusion is also associated with depressed mitochondrial function, particularly in subsarcolemmal mitochondria which are rapidly injured as a result of both ischemic and reperfusion conditions. Preservation of mitochondrial function with dissimilar approaches such as carnitine or phosphatidylcholine administration markedly reduces reperfusion injury-. A nonpharmacological novel approach towards the protection of the reperfused myocardium represents the induction of so-called stress or heart shock proteins in the heart prior to initiation of ischemia and reperfusion. The salutary effect of the heat shock response may be dependent not on the heat shock proteins themselves, but through the concomitant elevation of tissue catalase content resulting in enhanced detoxification of intracellular hydrogen peroxide. Thus reperfusion injury represents numerous complex events such that manipulations aimed at limiting such injury can be initiated to prevent specific defects with the ultimate goal of an overall reduction in cell damage.

Animals↗

PubMed1991

Concentration-dependent effects of protein kinase C-activating and -nonactivating phorbol esters on myocardial contractility, coronary resistance, energy metabolism, prostacyclin synthesis, and ultrastructure in isolated rat hearts. Effects of amiloride.

An extensive investigation of the cardiac actions of phorbol esters and the potential role of the Na(+)-H+ exchanger in those actions was carried out using isolated rat hearts. Sixty minutes of perfusion with 10(-9) M phorbol 12-myristate 13-acetate (PMA) or 10(-8) M phorbol 12,13-dibutyrate (PDBu) produced marked cardiac dysfunction associated with depressed contractility, coronary constriction, and elevated resting tension, the latter being particularly evident with PMA. These effects were also associated with disturbances in tissue levels of energy metabolites manifested primarily by a reduction in ATP and an elevation in lactate. Furthermore, both phorbols produced a sustained stimulation of the release of 6-ketoprostaglandin F1 alpha (6-keto PGF1 alpha), the hydrolysis product of prostacyclin (prostaglandin I2). Amiloride, an inhibitor of the Na(+)-H+ exchanger, significantly attenuated the loss in contractility and elevation in coronary pressure as well as the stimulated release of 6-keto PGF1 alpha but was without effect on elevations in resting tension or on changes in energy metabolites. Increasing concentrations of PMA or PDBu 10-fold resulted in a much more rapid and severe (greater than 80% loss in contractile function after 30 minutes) effect that was nonetheless qualitatively identical to that seen with the lower concentrations of phorbol. However, the effects were not prevented by amiloride. Surprisingly, 4 alpha-phorbol 12,13-didecanoate (alpha-PDD, 10(-6) M), which does not activate protein kinase C, was found to be a potent inhibitor of cardiac function (greater than 80% loss in contractility and 50% increase in resting tension) after 30 minutes of perfusion, although these effects were not associated with changes in levels of energy metabolites or with elevations in coronary pressure. Similarly, none of the actions of this compound were attenuated by amiloride. In contrast to the sustained effects of other phorbols on 6-keto PGF1 alpha release, the effect of alpha-PDD was transient (less than 10 minutes). In all hearts studied, the marked depression in contractile function caused by all phorbol esters occurred in the absence of any ultrastructural changes. 4 alpha-Phorbol (10(-6) M), which does not activate protein kinase C, was without effect on any parameter studied. Our results demonstrate very complex effects of phorbol esters on numerous parameters of cardiac function, including an amiloride-sensitive component that occurs at low concentrations. The latter observation suggests the involvement of Na(+)-H+ exchange activation, possibly occurring as a consequence of protein kinase C stimulation, in mediation of the effects of phorbol esters at low concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiloride↗

PubMed1990

Reduction of phosphate-induced dysfunction in rat heart mitochondria by carnitine.

The direct effects of varying concentrations (5-40 mM) of D,L-carnitine were studied in two populations, subsarcolemmal and interfibrillar, of cardiac mitochondria exposed to inorganic phosphate (Pi). After 5 min preincubation 20 mM Pi significantly depressed oxidative phosphorylation rate and ADP/ATP translocase activity, in both populations. Inclusion of D,L-carnitine during preincubation significantly prevented the Pi-induced depression in oxidative phosphorylation without affecting the ADP/ATP translocate system. The Pi-induced inhibition in mitochondrial oxygen consumption rate was seen with either pyruvate-malate, glutamate-malate or succinate as respiratory substrates and was also observed in uncoupled mitochondria treated with 2,4-dinitrophenol. Mitochondrial swelling and shrinkage studies revealed Pi-induced inner membrane instability, a phenomenon prevented by D,L-carnitine in a dose-dependent manner. The effect of Pi was also observed at a concentration of 5 mM which was also prevented by carnitine. Mepacrine, a phospholipase A2 inhibitor, failed to prevent any of the effects of Pi. The results therefore suggest that Pi can produce a depression in mitochondrial oxidative phosphorylation through a mechanism possibly associated with disturbed inner membrane structure and function but apparently unrelated to phospholipase A2 activation. The salutary actions of carnitine may partly explain its protective effects in the ischemic and reperfused heart, a phenomenon associated with enhanced intracellular Pi accumulation.

Animals↗

PubMed1990

Improved post-ischemic ventricular recovery in the absence of changes in energy metabolism in working rat hearts following heat-shock.

We have previously demonstrated that induction of the heat-shock response in rats results in improved recovery of isolated Langendorff-perfused rat hearts subjected to low-flow ischemia followed by reperfusion (Currie et al., 1988). The mechanisms underlying this protective effect of heat-shock are uncertain although the protection was associated with enhanced content of the antioxidant enzyme catalase but not superoxide dismutase or glutathione peroxidase (Currie et al., 1988). Various investigators have suggested the importance of improved energy metabolism in determining recovery following ischemia (Pasque and Wechsler, 1984; Haas et al., 1984; Devous and Lewandowski, 1987). We therefore examined, using a working rat heart model subjected to 10 or 15 min zero flow ischemia whether changes in energy metabolites could account for the protective effect of the heat-shock response. Hearts perfused 24 h after induction of heat-shock failed to demonstrate significant improvement of recovery following 10 min ischemia, however recovery was significantly enhanced in hearts reperfused after 15 min ischemia. Ischemia produced a depression in both ATP and creatine phosphate (CP) content whereas a moderate elevation in ADP and AMP and a marked increase in tissue lactate were evident. These changes were unaffected by prior heat-shock treatment. For both durations of ischemia tissue metabolites were determined during early (5 min) and late (30 min) reperfusion. Although partial recovery in high energy phosphates and a return of ADP, AMP and lactate to near-normal levels were evident, no differences in energy products were observed between hearts from normal or heat-shocked animals, in spite of significantly enhanced recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗

PubMed1990

Protection of the reperfused ischemic isolated rat heart by phosphatidylcholine.

We examined phosphatidylcholine (PC) effects on the isolated rat heart subjected to low- or zero-flow ischemia followed by reperfusion. Untreated hearts subjected to 30 min of low-flow ischemia recovered 15% contractility following reperfusion compared to time-control hearts. Phosphatidylcholine (0.005%) addition either 10 or 20 min before ischemia significantly enhanced recovery to approximately 61% and reduced the incidence of arrhythmias during ischemia and reperfusion. Contracture during ischemia and reperfusion was significantly reduced when PC was added 20 min before ischemia. Phosphatidylcholine was ineffective when administered at the time of reperfusion except for a moderate reduction in arrhythmia development. Phosphatidylcholine also produced a salutary effect when added 20 min prior to zero-flow ischemia. Subsarcolemmal mitochondria (SLM) and, to a much lesser degree, interfibrillar mitochondria (IFM) of untreated hearts subjected to low-flow ischemia and reperfusion exhibited depressed oxidative phosphorylation which was prevented by PC. Both mitochondrial populations exhibited a marked depression in ADP/ATP translocase activity; however, this was generally unaffected by PC. Subsarcolemmal mitochondria but not IFM of zero-flow ischemic reperfused hearts also exhibited significantly depressed oxidative phosphorylation, which was unaffected by PC. Zero-flow ischemia produced a rapid and total cessation of contractility. Both populations exhibited a substantial PC-insensitive reduction in translocase activity. Our results demonstrate, for the first time, a protection by PC on the reperfused ischemic heart. The PC-induced protection following low-flow but not zero-flow ischemia is associated with improved SLM oxidative phosphorylation suggesting dissimilar contribution of mitochondria to reperfusion-associated myocardial injury.

Animals↗

PubMed1990

Mechanisms for cardiac depression induced by phorbol myristate acetate in working rat hearts.

1. The effects of the phorbol ester, phorbol myristate acetate (PMA) were examined on function and energy metabolism in the isolated working heart of the rat. 2. At a concentration of 10(-9) M PMA produced a rapid loss in cardiac function in terms of aortic flow rate (AFR) and coronary flow rates (CFR) whereas a similar concentration of 4 alpha-phorbol 12,13-didecanoate was ineffective. At a concentration of 10(-10) M, the PMA-induced depression was more gradual but nevertheless very pronounced with an almost total loss in AFR after 30 min perfusion. The reduction in CFR was more moderate than that observed with respect to AFR. 3. The protein kinase C (PKC) inhibitor (+/-)-1-O-hexadecyl-2-O-acylglycerol significantly attenuated the loss in AFR and CFR following addition of PMA. 4. Two inhibitors of Na+/H+ exchange, amiloride and quinacrine, totally prevented the reduction in AFR. Although the PMA-induced depression in CFR was also attenuated by both amiloride and quinacrine, these effects were not significant, probably reflecting the less pronounced effect of PMA on this parameter. 5. Nifedipine, a dihydropyridine calcium channel blocker reduced PMA toxicity to a similar degree as Na+/N+ exchange inhibition whereas the calcium channel agonist Bay K 8644 was without effect. 6. Tissue content of energy metabolites including high energy phosphates, total adenine nucleotides or lactate were not significantly affected by PMA perfusion. 7. We conclude that PKC activation is necessary for phorbol ester-induced cardiac dysfunction. The consequence of PKC stimulation includes (1) Na+/H+ exchange activation and a subsequent elevation in intracellular calcium [Ca2+]i via Na+/Ca2+ exchange and (2) PKC-dependent phosphorylation of the calcium channel, both of which would produce toxicity by elevation of [Ca21]i. Pharmacological manipulation of any of these steps prevents PMA toxicity by virtue of a reduction in the accumulation of [Ca21]i. PMA effects or their prevention are unrelated to any changes in energy metabolism.

Amiloride↗

PubMed1990

Acquisition and decay of heat-shock-enhanced postischemic ventricular recovery.

Hyperthermia induces the synthesis of the 71-kDa heat-shock protein (heat-shock response) in all rat tissues, including heart. We examined whether induction of the heat-shock response alters the response of isolated hearts to ischemia and reperfusion. Anesthetized male rats were pretreated with 15 min of hyperthermia (42 degrees C) and then recovered for 0, 24, 48, 96, or 192 h. Hearts were isolated from control and hyperthermia-treated rats and retrogradely perfused. Greatest recovery occurred in 48-h postheat-shock hearts; after 30 min of reperfusion there was a 38, 62, and 62% recovery of force, +dF/dt, and -dF/dt, respectively, and 17, 36, and 30% recovery, respectively, for the control hearts. Creatine kinase efflux during reperfusion was reduced by 75% for 24-h postheat-shock hearts. The antioxidative enzyme catalase was increased 24, 48, and 96 h posthyperthermia. Treatment of rats with 3-amino-1,2,4-triazole (1 g/kg body wt), which irreversibly inactivates catalase, 30 min before isolation of hearts, abolished the hyperthermia-induced enhancement of postischemic recovery. These results show a strong relationship between the acquisition and decay of the enhanced postischemic ventricular recovery and the hyperthermic induction of the heat-shock response indicated by the accumulation of heat-shock protein HSP71 (mol mass 71 kDa) and the increase in catalase activity.

Amitrole↗

PubMed1990

Positive inotropic effects of low concentrations of leukotrienes C4 and D4 in rat heart.

We examined the effects of leukotrienes (LT) B4, C4, D4, and E4 (0.010-2.5 ng/ml) on contractile and coronary function in isolated rat hearts. Concentration-dependent effects were examined either by the cumulative addition of LTs or by addition of specific concentrations to individual preparations. Neither LTB4 nor LTE4 produced myocardial or coronary effects at any concentration, irrespective of addition protocol. At 0.010 ng/ml, both LTC4 and LTD4 produced an increase in force that was associated with a 30% elevation in coronary pressure. Further cumulative addition of either leukotriene resulted in a negative inotropic effect and a further increase in coronary pressure. In contrast, following single additions of LTC4 or LTD4 (0.01-0.50 ng/ml) a positive inotropic effect and an increased coronary pressure were observed. LTC4 or LTD4 at 0.5 ng/ml produced a negative inotropic effect in hearts pretreated with 0.01 ng/ml of LTD4 or LTC4, respectively. Reversal of this addition protocol resulted in a negative inotropic effect of either 0.01 ng/ml LTD4 or LTC4. Verapamil and nifedipine significantly attenuated the positive inotropic and coronary constricting effect of 0.5 ng/ml LTC4 and LTD4. The addition of either LT following BAY K 8644 resulted in a negative inotropic effect, in contrast to the positive inotropic influence seen with leukotriene alone. Our results demonstrate a positive inotropic effect of low concentrations of LTC4 and LTD4 concomitant with coronary artery constriction, a phenomenon determined by leukotriene addition protocols and suggestive of LTC4/LTD4 receptor interaction. The effects of calcium channel antagonists and BAY K 8644 on the inotropic response suggest a leukotriene-mediated activation of the calcium channel resulting in increased intracellular calcium concentrations.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Effect of verapamil on phosphate-induced changes in oxidative phosphorylation and atractyloside-sensitive adenine nucleotide translocase activity in two populations of rat heart mitochondria.

Phosphate (Pi)-induced depression in cardiac mitochondrial function was studied using mitochondria isolated by two different procedures which purportedly yield two distinct populations. Subsarcolemmal mitochondria (SLM) exhibited an enhanced sensitivity to 20 mM Pi with respect to oxidative phosphorylation. Thus, a significant depression in oxidative phosphorylation in this population was seen following only 1-min treatment, whereas interfibrillar mitochondria (IFM) were unaffected. Both populations showed a similar response to 5-min treatment with Pi. The Pi-induced depression in respiration was partially, although significantly, reversed by a 50 microM concentration of the calcium antagonist verapamil, an observation which suggests a contribution of calcium to the Pi-induced defect in respiration. Pi also produced a potent inhibition of ADP uptake in both mitochondrial populations, which was in close agreement to Pi-induced modification of low amplitude shrinkage-swelling responses following ADP addition. Both of these parameters were unaffected by verapamil. Our results show an enhanced sensitivity of SLM to a verapamil-sensitive Pi-induced depression in oxidative phosphorylation. However, the potent, verapamil-insensitive decrease in adenine nucleotide translocase activity by Pi demonstrates that calcium is likely only partially involved in Pi-induced depression in oxidative phosphorylation and that a further partial contribution arises from a decrease in adenine nucleotide translocase activity.

Adenosine Diphosphate↗

PubMed1989

Acute effects of hypoxia and phosphate on two populations of heart mitochondria.

Initial Polytron treatment with subsequent exposure to the bacterial proteinase Nagarse has been shown to result in the isolation of two distinct populations of cardiac mitochondria, subsarcolemmal and interfibrillar mitochondria, respectively. Although these populations have been shown to possess distinct biochemical properties, few studies have been reported which document the potential differences in their response to pathological insult. We therefore examined the effect of acute hypoxia with or without reoxygenation as well as treatment with phosphate on oxidative phosphorylation on both groups of mitochondria. Freshly-isolated interfibrillar mitochondria (IFM) exhibited significantly higher respiratory values, with the exception of the ADP:O ratios, than subsarcolemmal mitochondria (SLM). With pyruvate-malate as respiratory substrate, 40 minutes hypoxia alone produced no effect on SLM whereas a stimulation in respiration was seen in IFM. A 40-minute reoxygenation period depressed the oxidative phosphorylation rate in SLM whereas it was stimulated in IFM. These treatments did not produce any effect in either population when succinate was the substrate of choice. Because of the latter observation, the possibility that increased lability of complex I of the electron transport chain accounted for the differences associated with NAD-linked substrates was studied by assessing NADH oxidation of sonicated mitochondria following the treatments. SLM exhibited enhanced permeability to exogenous NADH as well as increased sensitivity to sonication following either hypoxia or hypoxia/reoxygenation compared to IFM. Compared to hypoxia/reoxygenation, increasing concentrations of phosphate (5-15 mM) produced a marked depression in oxidative phosphorylation of SLM whereas IFM were relatively resistant. The toxic effects of phosphate were much more evident with pyruvate-malate as substrates; with succinate, oxidative phosphorylation of IFM was not depressed by phosphate whereas only a slight depression was observed with SLM. The latter population similarly exhibited reduced NADH oxidation following phosphate treatment whereas IFM were unaffected. Our studies show a differential sensitivity of two mitochondrial populations to hypoxia/reoxygenation, and, more markedly to phosphate. Since these effects were much less pronounced with succinate-linked respiration and since they were associated with defective NADH oxidation in SLM, it is suggested that the differences between the two populations may be accounted for by the increased lability of complex I of SLM due to hypoxia/reoxygenation or phosphate.

Animals↗

PubMed1989

Inhibition of post-ischemic ventricular recovery by low concentrations of prostacyclin in isolated working rat hearts: dependency on concentration, ischemia duration, calcium and relationship to myocardial energy metabolism.

The objective of this study was to characterize the effect of prostacyclin (PGI2) on ventricular function following total global ischemia in isolated working rat hearts and to investigate the mechanism of its action. Ischemia was initiated for 10, 15, 20 or 25 min with or without treatment with PGI2. Increasing durations of ischemia resulted in a progressive decline in high energy phosphate (HEP) stores, an elevation in tissue lactate, and incomplete recovery of function with reperfusion. Prostacyclin at either 1 or 10 ng/ml had no effect on HEP levels or total adenine nucleotides, and tissue lactate was not significantly affected by PGI2 in hearts made ischemic for 10 to 20 min, but both PGI2 concentrations significantly elevated lactate levels after 25 min ischemia. Reperfusion recovery of left ventricular function was complete following 10 and 15 min ischemia, but incomplete recovery was evident following 20 min ischemia (77% of pre-ischemic function); and although PGI2 had no direct effect on the function of aerobically perfused hearts, recovery of aortic flow with 1 ng/ml PGI2 after 20 min of ischemia was reduced to approximately 20% (P less than 0.01). This depression in recovery was associated with significantly increased lactate levels during reperfusion. At a concentration of 10 ng/ml PGI2 did not depress ventricular recovery or elevate lactate content after 20 min ischemia. When hearts made ischemic for 20 min were analyzed, a significant negative correlation was found between ventricular recovery (aortic flow rate) and lactate concentration; however, no correlation existed between recovery and ATP levels. After 25 min of ischemia, five of eight (62.5%) untreated hearts demonstrated some degree of ventricular recovery, however, only two of ten hearts studied demonstrated any measurable functional recovery with either PGI2 concentration. This effect of PGI2 to reduce or prevent recovery of ventricular function following either 20 or 25 min of ischemia as well as the corresponding elevation in lactate levels was prevented by treatment with the calcium channel blocker verapamil. This study therefore shows that PGI2 at critical low concentrations can depress left ventricular recovery following total ischemia. This effect of PGI2 becomes more pronounced as ischemia duration is prolonged and is associated with elevated tissue lactate levels. The studies with verapamil suggest that PGI2 may be acting via the slow calcium channel to increase lactate levels and depress ventricular recovery following prolonged periods of ischemia.

Adenine Nucleotides↗

PubMed1989

Effect of D,L-carnitine on the response of the isolated heart of the rat to ischaemia and reperfusion: relation to mitochondrial function.

1. The effect of 100 microM (20 micrograms ml-1) of D,L-carnitine was studied on the isolated heart of the rat subjected to 30 min of low flow ischaemia followed by reperfusion. 2. In untreated hearts (n = 30) ischaemia produced an almost total loss of contractility (P less than 0.05 compared with non-ischaemic time control) which was accompanied by an increase in resting tension of approximately 235% (P less than 0.05). Ventricular arrhythmias developed during ischaemia in 100% (P less than 0.05) of untreated hearts studied. Following reperfusion, untreated hearts recovered 16.3% of contractile function and demonstrated a 60% elevation in resting tension. The incidence of reperfusion-associated ventricular fibrillation was 60%. 3. Carnitine treatment produced no effect on either the contractile depression or the elevation in resting tension during ischaemia but did significantly decrease the incidence of arrythmias at the termination of ischaemia to 63.3% (n = 30, P less than 0.05). In the presence of carnitine, contractile recovery at the end of reperfusion was significantly increased to 30.2% (n = 10, P less than 0.05) and the elevation in resting tension was decreased to 30% (n = 10, P greater than 0.05). The incidence of ventricular arrhythmias during reperfusion was significantly reduced by carnitine. 4. Two populations of mitochondria, subsarcolemmal (SLM) and interfibrillar (IFM) isolated at the end of the ischaemic period exhibited an overall increase in oxidative phosphorylation rates as well as uncoupled oxygen consumption; both phenomena were more pronounced with IFM. Carnitine generally potentiated this response. A 29% and 38% inhibition in atractyloside-sensitive ADP uptake was observed in SLM and IFM, respectively, following ischaemia, which was partially prevented by carnitine. 5. After 10min of reperfusion, adenosine diphosphate (ADP) uptake in SLM was further reduced to 55% of control whereas with IFM, uptake was not different from that seen at the end of ischaemia. Mitochondria isolated from hearts after 30 min of reperfusion revealed a significantly depressed oxidative phosphorylation as well as ADP/ATP translocase activity. These defects were partially reversed in hearts perfused with carnitine. 6. Our study demonstrates that D,L-carnitine protects the rat isolated heart against injury associated with ischaemia and reperfusion through a mechanism associated with improved mitochondrial function.

Animals↗

PubMed1989

Relationship between oxidative phosphorylation and adenine nucleotide translocase activity of two populations of cardiac mitochondria and mechanical recovery of ischemic hearts following reperfusion.

The possible relationship of the atractyloside-sensitive adenine nucleotide translocase activity, oxidative phosphorylation, and the recovery of ventricular contractility following reperfusion of the ischemic isolated rat heart was studied. Five minutes of total global ischemia without reperfusion produced a significant depression in adenine nucleotide translocase in subsarcolemmal mitochondria (SLM), whereas a minimum of 10 min ischemia was required to observe a significant depression in interfibrillar mitochondria (IFM). Increasing durations of ischemia resulted in a progressively larger depression in translocase activity, with a maximum depression of approximately 75% seen in both populations following 20 min ischemia. In contrast, oxidative phosphorylation was totally unaffected in either mitochondrial population following up to 20 min of ischemia. We assessed whether translocase activity or oxidative phosphorylation were related to contractile recovery in hearts reperfused following various durations of ischemia. In SLM, translocase activity was further depressed following reperfusion compared with pre-reperfusion ischemic values, whereas with IFM only reperfusion following 5 min ischemia produced a further depression in translocase values. Oxidative phosphorylation rates of SLM and IFM were significantly depressed following reperfusion of ischemic hearts, although SLM exhibited a generally higher sensitivity in this regard. In reperfused hearts, an overall significant relationship was found between oxidative phosphorylation rate and adenine translocase activity as well as between translocase activity and post-reperfusion contractile recovery. These data show that ischemia can produce a significant depression in translocase activity in the absence of any change in oxidative phosphorylation. The results also suggest that the depression in mitochondrial ADP/ATP translocase and subsequent inhibition of oxidative phosphorylation in the reperfused heart may represent one of the important contributory mechanisms involved in cardiac failure and injury during acute ischemia and reperfusion.

Animals↗

PubMed1989

A direct role of endogenous prostaglandins in reperfusion-induced cardiac arrhythmias.

The possible role of prostaglandins (PG) in arrhythmias associated with ischemia and reperfusion was studied in isolated, superfused canine Purkinje tissues. Ischemic conditions caused partial depolarization and decrease of excitability. Neither inhibition of PG synthesis (ibuprofen, 30 micrograms/mL) nor addition of exogenous PGF2 alpha (1 ng/mL) modified responses to "ischemia." Reperfusion with normal Tyrode's solution stimulated PG production (measured as 6-keto-PGF1 alpha) and induced a series of electrophysiological events. Under control conditions, Purkinje fibres rapidly repolarized. Subsequently, these tissues began to depolarize and oscillatory afterpotentials appeared. Purkinje tissues depolarized further and became temporarily inexcitable. Return of activity was associated with depolarization-induced automaticity. Ibuprofen prevented reperfusion-stimulated PG release. Ibuprofen also increased the magnitude of early repolarization and greatly attenuated subsequent depolarization. Depolarization-induced automaticity was not observed under these conditions; however, oscillatory afterpotentials were not abolished by ibuprofen. Addition of PGF2 alpha to "ischemic" and reperfusion solutions in the presence of ibuprofen restored the arrhythmogenic responses. We conclude that release of endogenous prostaglandins contributes to electrophysiological changes elicited by reperfusion in canine Purkinje fibres.

Animals↗

PubMed1989

Synthesis and relevance of cardiac eicosanoids with particular emphasis on ischemia and reperfusion.

Eicosanoids represent a family of compounds derived primarily from arachidonic acid. It is now known that arachidonic acid can undergo metabolism via at least three distinct pathways, although the most readily understood are those resulting in prostaglandin or leukotriene formation via cyclooxygenase and 5-lipoxygenase, respectively. These products can be synthesized by the heart or can be released from accumulating neutrophils under various pathological conditions. Eicosanoids possess a wide array of pharmacological actions that could be of importance either in the initiation or modulation of various cardiac diseases. Here, we review the potential importance of eicosanoids to ischemic heart disease. Data are cited that examine the potential importance of these compounds to experimentally induced cardiac injury as well as clinically observed ischemic heart disease. Particular emphasis is placed on recent studies that document the relevance of endogenously synthesized arachidonic acid metabolites as well as the consequence of modulating eicosanoid synthesis through pharmacological or dietary means on cardiac injury under experimental or clinical situations.

Coronary Disease↗

PubMed1989

A rapid phosphate-induced depression of heart subsarcolemmal mitochondrial oxidative phosphorylation.

Inorganic phosphate (Pi) was added to suspensions of interfibrillar (IFM) and subsarcolemmal (SLM) mitochondria. With 20 mM Pi, significant depression in SLM oxidative phosphorylation was seen after 60 seconds exposure whereas 120 seconds was required to depress IFM, although to a lesser degree. Oxidative phosphorylation rate of SLM was significantly depressed by 1 minute incubation with 2.5-20 mM Pi, whereas IFM were unaffected. Five minute incubation with similar Pi concentrations produced equal depression in both populations. We postulate that the rapid increase in intracellular Pi may contribute to contractile failure associated with early ischemia by depressing a critical pool of ATP synthesis represented by SLM.

Animals↗