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S Genade

Publications and source records attributed to S Genade.

31 records · Page 2Linked to original sources
PubMed1994

Halothane protects the isolated rat myocardium against excessive total intracellular calcium and structural damage during ischemia and reperfusion.

A recent study from our laboratory demonstrated halothane to be a powerful protectant of the isolated rat heart during reperfusion after normothermic cardioplegic arrest. It was speculated that this protective effect might be due to prevention of excessive intracellular calcium. The aim of the present study was to evaluate the effect of halothane on the total intracellular calcium (Ca2+) content and on myocardial structure both at the end of normothermic cardioplegic arrest and at the end of reperfusion. Isolated perfused rat hearts were perfused for a control period of 30 min, followed by 40 min of normothermic cardioplegic arrest with or without reperfusion for 30 min. Halothane (1.5%) was administered continuously before and after arrest. Halothane caused a significant decrease of intracellular Ca2+ at the end of normothermic cardioplegic arrest and after reperfusion. Myocardial morphology was assessed by extensive light microscopy and ultrastructure was evaluated by electron microscopy. Grading of ischemic damage showed that exposure to normothermic cardioplegia resulted in marked ischemic injury, regardless of whether the hearts were treated with halothane. Reperfusion in the presence of halothane caused a significant reversal of ischemic damage and almost complete ultrastructural repair, whereas untreated hearts still exhibited severe edema, contracture, and contracture bands. Our results indicate that the beneficial effects of halothane on myocardial structural recovery during reperfusion is associated with a reduction in excessive intracellular Ca2+. The exact mechanism of this protective action is under investigation.

Animals↗
PubMed1994

Preconditioning with hypoxia versus global ischemia in the isolated rat heart: effect on function and metabolism.

It has recently been shown that hypoxia and ischemia are equally effective to precondition the myocardium of the rat. A comparison of the metabolic changes caused by transient ischemia and hypoxia has not yet been made and may help to elucidate the metabolic factors involved in eliciting preconditioning. The aim of this study was to compare the changes in tissue high energy phosphates, glycogen and lactate during and after hypoxic and ischemic preconditioning in isolated perfused rat hearts. Isolated rat hearts were subjected to global ischemia of 30 minutes duration, with and without preconditioning consisting of a single episode of 5 minutes global ischemia or hypoxia (PO2 = 12kPa). The post-ischemic recovery of aortic flow of the nonpreconditioned group was significantly less than that of the two preconditioned groups: 0.5 +/- 0.5 ml/min vs. 23.3 +/- 3.4 and 20.7 +/- 3.6 ml/min for ischemic and hypoxic preconditioning respectively. The only common metabolic factor between the two preconditioned groups was the similar extent of glycogenolysis after transient ischemia or hypoxia: glycogen decreased from 22 +/- 0.8 in non-preconditioned hearts to 16 +/- 0.5 and 16 +/- 1.5 mumoles glucose per g wet tissue in ischemic and hypoxic preconditioned hearts respectively. There was also no difference in lactate production between the two groups during the sustained episode of ischemia. We conclude that oxygen deprivation, rather than other metabolic factors, is the important factor in eliciting preconditioning.

Animals↗
PubMed1993

Effects of beta-blockers and Ca(2+)-antagonists on the response of the isolated working rat heart to adrenergic stimulants after cardioplegic arrest.

During coronary artery bypass graft (CABG) surgery, patients pretreated with the combination of beta-blocking drugs and Ca2+ antagonists for control of myocardial ischemia often respond inadequately to adrenergic stimulants administered after cardioplegic arrest. In this study, the effects of the combination of a beta-blocker (propranolol) and a Ca2+ antagonist (nifedipine) on the spontaneous recovery, as well as the adrenergic response of the isolated, perfused, working rat heart after a period of cardioplegic arrest were evaluated. After pretreatment of the animals with propranolol and/or nifedipine, hearts were removed, perfused in the presence of pretreatment drugs, subjected to 45 minutes of normothermic cardioplegic arrest, reperfused, and finally stimulated with exponentially increasing concentrations of a sympathomimetic drug. Propranolol, and to a lesser extent nifedipine, protected the hearts during cardioplegic arrest, as indicated by the improved recovery and maximum response to adrenergic stimulation after cardioplegia. Isoprenaline, a beta-stimulant, (at a 100 x higher than conventional concentration), elicited an adequate inotropic and chronotropic response. Stimulation by the alpha, beta-stimulant adrenaline or dobutamine improved only the inotropic response of propranolol and combination treated hearts. Cautious extrapolation of the results to human may suggest continuation of drug therapy of patients before CABG surgery.

Adenine Nucleotides↗
PubMed1993

Enflurane and isoflurane reduce reperfusion dysfunction in the isolated rat heart.

We evaluated the possible cardioprotective effects of enflurane (E) and isoflurane (I) in isolated rat hearts subjected to 40 min normothermic arrest. After reperfusion, hearts were stimulated with adrenaline to evaluate their systolic reserves. In hearts not receiving I or E, adenosine triphosphate (ATP) was reduced from 23.0 +/- 0.8 to 9.3 +/- 1.1 mumol/g dry weight (means +/- SEM; P < 0.001) after arrest. This was associated with a significant reduction in ventricular work (Wt) from 13.6 +/- 0.7 to 1.6 +/- 0.7 mW (P < 0.001). Adrenaline partially restored Wt but not the ATP. E and I given only during normothermic arrest (in the cardioplegic solution) resulted in reductions in ATP similar to the hearts not receiving the drugs. However, on reperfusion and subsequent administration of adrenaline, hearts subjected to the anesthetic drugs performed as well as hearts before arrest. For example, in hearts not exposed to I or E, the Wt after the elective arrest was 1.55 +/- 0.05% (mean +/- SEM) of the pre-arrest value. This was significantly less than hearts exposed to either one of the inhalational agents (40.02 +/- 3.49% of the pre-arrest value; P < 0.0001). Adrenaline improved function in hearts which did not receive I or E to 55.02 +/- 12.80% of the pre-arrest value, but this was significantly less than the Wt performed by the hearts exposed to the anesthetic agents (122.67 +/- 7.78% of pre-arrest value; P < 0.001). This beneficial effect of I and E during reperfusion probably is mediated by the effect of the anesthetic agents on Ca2+ slow channels. The effect could not be ascribed to depression of global myocardial contractile function associated with I and E.

Adenosine Triphosphate↗
PubMed1993

Effect of captopril on changes in rats' hearts induced by long-term irradiation.

The aim of this study was to test the efficacy of captopril, an angiotensin-converting enzyme inhibitor and a known suppressor of fibrosis, in preventing late radiation-induced cardiac pathology. Myocardial functional, histochemical and ultrastructural-morphometric studies were done on perfused hearts of rats isolated 3 and 6 months after 60Co gamma irradiation with 20 Gy and age-matched controls. At each time the animals were divided into the following groups: nonirradiated controls; irradiated once with 20 Gy; irradiated as above and given daily doses of captopril; daily doses of captopril without irradiation. The results showed that captopril, while ameliorating the decrease in the indices of capillary function, increase in mast cells, fibrosis, number of atrial granules, and changes in nerve terminals, failed to prevent the progressive functional deterioration of the hearts after irradiation. These findings suggest that an intramyofiber derangement may be involved in the long-term myocardial complications of irradiation.

Animals↗
PubMed1992

The effect of ischaemia-reperfusion on [3H]inositol phosphates and ins(1,4,5)P3 levels in cardiac atria and ventricles--a comparative study.

In this study incorporation of [3H]inositol into inositol phosphates and phosphoinositides as well as tissue Ins(1,4,5)P3 levels of the atria and ventricles of isolated, perfused rat hearts were compared. Although the incorporation of [3H]inositol into the phosphoinositides of atria and ventricles was similar, significantly higher (2-3 fold) incorporation rates into inositol phosphates were observed in atrial tissue. Using a D-myo-[3H]Ins(1,4,5)P3 assay system, the Ins(1,4,5)P3 levels observed in atria from perfused rat hearts were also significantly higher than those obtained under the same experimental circumstances in the ventricles. Since previous studies on whole hearts showed inhibition of the phosphatidylinositol (PI) pathway during ischaemia with an immediate significant stimulation upon reperfusion [12, 20], the effects of ischaemia and 1 min postischaemic reperfusion were also examined separately in atria and ventricles. The results showed that 20 min of global ischaemia significantly depressed Ins(1,4,5)P3 levels as well as incorporation of [3H]inositol into ventricular InsP2 and InsP3. Reperfusion caused an immediate (within 1 min) increase in Ins(1,4,5)P3 levels and also [3H]inositol incorporation into all three cytosolic inositol phosphates in the ventricles. However, the effect of ischaemia and reperfusion on Ins(1,4,5)P3 levels as well as the incorporation of [3H]inositol into the inositol phosphates were less prominent in the atria. It therefore appears that the differential responses of the atria and the ventricles to an oxygen deficiency [41] are also reflected in the differences in PI metabolism during ischaemia-reperfusion.

Animals↗
PubMed1992

The role of alpha 1-adrenergic stimulation in inositol phosphate metabolism during post-ischaemic reperfusion.

The aim of this study was to elucidate the mechanism of enhanced inositol phosphate metabolism during reperfusion. Inositol phosphate stores were prelabelled by perfusing isolated rat hearts for 1 h with [3H]inositol (1.5 microCi/ml). LiCl (10 mM) and prazosin (0.3 microM) were subsequently added 15 min before (i) 20 min control perfusion; (ii) 20 min normothermic ischaemic cardiac arrest (NICA); (iii) 20 min NICA followed by 1 min reperfusion. The ventricles were freeze-clamped before determination of isotopical incorporation of [3H]inositol into the inositol phosphates (Dowex anion exchange chromatography) and InsP3 levels (Amersham InsP3 assay system). In addition, noradrenaline release into the perfusate was also assessed (HPLC and electrochemical detection). The results showed: (i) increased noradrenaline release into the perfusate immediately after the onset of reperfusion; (ii) significant depression of [3H]inositol incorporation into inositol phosphates and InsP3 levels after 20 min NICA; (iii) reperfusion caused an immediate significant increase in isotopical incorporation of [3H]inositol into inositol phosphates as well as InsP3 levels; (iv) the alpha 1-adrenergic blocker, prazosin (0.3 microM), completely inhibited the reperfusion-induced increase in inositol phosphate metabolism. These observations suggested that increased alpha 1-adrenergic receptor stimulation by noradrenaline might be responsible for the stimulation of ventricular inositol phosphate metabolism during postischaemic reperfusion.

Animals↗
PubMed1991

Myocardial membrane cholesterol: effects of ischaemia.

Evidence has recently been presented that myocardial ischaemia is associated with a significant increased mitochondrial cholesterol content, suggesting a redistribution of cholesterol within the ischaemic cell (Rouslin et al. 1980, 1982). The aim of this study was therefore to determine the effects of different periods of ischaemia and reperfusion on the cholesterol content of myocardial mitochondria, sarcoplasmic reticulum and sarcolemma. Using the isolated perfused rat heart as experimental model, it was demonstrated that increasing periods of ischaemia (15-60 min) caused a progressive loss of cholesterol from the tissue as well as from the sarcolemma and sarcoplasmic reticulum, concomitant with a significant increase in mitochondrial cholesterol content. These compositional changes were associated with a marked increase in sarcolemmal and mitochondrial microviscosity, while that of the sarcoplasmic reticulum was reduced. To gain more insight into the mechanisms controlling intracellular cholesterol distribution, control and ischaemic hearts were perfused with either exogenous cholesterol or its precursor [U-14C]acetate as an indicator of endogenous cholesterol synthesis. Perfusion with exogenous cholesterol resulted in significant increases in the membrane cholesterol content of control hearts. However, hypoxic, low flow perfusion prevented cholesterol enrichment of the sarcolemmal and sarcoplasmic reticulum membranes, while the cholesterol content of the mitochondria was increased from 99.48 +/- 12.75 to 127.61 +/- 1.84 nmols/mg protein, indicating specific incorporation into this membrane system. Incorporation of [U-14C]acetate into cholesterol in the sarcoplasmic reticulum was increased by 120% in ischaemic conditions. However, a marked redistribution of newly synthesized cholesterol was observed within the ischaemic cell: under control conditions most of the labelled cholesterol was transferred to the sarcolemma and least to the mitochondria, while this distribution pattern was reversed in ischaemia. In view of the fact that exchange of cholesterol between membranes is affected by both phospholipid polar head-group composition and acyl chain length and saturation, it is suggested that prior ischaemia-induced membrane compositional changes might lead to intracellular cholesterol redistribution. Finally, to determine whether cholesterol loss affects sarcolemmal permeability, hearts enriched in sarcolemmal cholesterol were subjected to 15 or 30 min global ischaemia followed by reperfusion and the rate of enzyme release determined. However, enzyme release was similar in treated and untreated hearts, indicating that sarcolemmal cholesterol loss probably does not affect its permeability.

Animals↗
PubMed1991

Halothane does have protective properties in the isolated ischemic rat heart.

To determine whether halothane has protective effects on the ischemic heart, the influence of various concentrations (0.5%-1.5%) of halothane on metabolic and functional recovery during reperfusion after 60-min hypothermic (20 degrees C) and 40-min normothermic cardioplegic arrest was determined in the isolated rat heart. Halothane was administered either before and after arrest or intermittently during arrest. Hearts not receiving halothane demonstrated a reduction in adenosine triphosphate (ATP) content from a control value of 20.35 +/- 1.66 mumol/g dry wt (mean +/- SEM) (before arrest) to 9.34 +/- 1.12 mumol/g dry wt at the end of arrest (P less than 0.001). The myocardial ATP content, when measured 20 min after arrest and during reperfusion, remained decreased (9.57 +/- 0.62 mumol/g dry wt). Under these experimental conditions, aortic flow was reduced from 43.62 +/- 2.40 mL/min before arrest to 1.80 +/- 1.80 mL/min 20 min after arrest and during reperfusion (P less than 0.001). The administration of adrenaline after 20 min of reperfusion resulted in partial recovery to 22.01 +/- 8.36 mL/min. Administration of halothane (0.5%) before the cardioplegic period was associated with a reduction of ATP at the end of the normothermic arrest (4.02 +/- 0.38 mumol/g dry wt; P less than 0.01), but the ATP increased significantly (13.45 +/- 0.32 mumol/g dry wt) when measured after the arrest and after 20 min of reperfusion and stimulation with adrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMedDate not supplied

A comparison between ischemic preconditioning and anti-adrenergic interventions: cAMP, energy metabolism and functional recovery.

OBJECTIVES: The postulate that ischemic preconditioning caused an attenuation in ischemia induced increases in tissue cAMP, and that this may pertain to the mechanism of ischemic preconditioning, was investigated in the isolated rat heart. A significant reduction in tissue cAMP in preconditioned hearts was observed for all time periods of global ischemia studied. The significance of this observation was evaluated by comparing the effect of anti-adrenergic interventions on energy metabolism and post-ischemic functional recovery of both non-preconditioned and preconditioned hearts. METHODS: The isolated perfused rat heart was used as experimental model. Six groups were studied: Non-preconditioned rat hearts: i) untreated controls (Non-PC), ii) reserpinised (Non-PC Res), iii) propranolol treated (10(-7) M) (Non-PC Prop); Preconditioned rat hearts: iv) preconditioned controls (PC), v) reserpinised (PC Res) and vi) propranolol (10(-7) M) treated (PC Prop). RESULTS: After 25 min global ischemia the concentration of cAMP was increased by 79.6% in the Non-PC group. This increase was attenuated in all of the treated groups, although in varying degrees. Energy utilization in these hearts also differed markedly between the groups. Functional recovery was however similar in all Non-PC and PC treated groups and significantly superior to that of Non-PC control hearts. Prior reserpinisation mimicked the protective effect of preconditioning on energy metabolism and functional recovery. To determine the significance of attenuation of the increase in cAMP in the protection conferred by preconditioning, hearts were pretreated with forskolin (10(-6) M). This caused an accumulation of tissue cAMP in preconditioned hearts to similar absolute values as seen in untreated non-preconditioned hearts during 25 min global ischemia. However, the percentage increase in forskolin-pretreated preconditioned hearts during sustained ischemia was only 50% vs. 71% in non-preconditioned hearts treated with forskolin, confirming an attenuated beta-response induced by preconditioning. Forskolin treatment of preconditioned hearts did not abolish the protective effect. CONCLUSIONS: The findings suggest that the protection against ischemic damage conferred by preconditioning is associated with an attenuated beta-adrenergic response. However, whether the changes in cAMP occurring during sustained global ischemia is the cause of consequence of the elicited protection, remains to be established.

Adenine Nucleotides↗
PubMedDate not supplied

Opioid receptor stimulation acts as mediator of protection in ischaemic preconditioning.

Involvement of the opioid receptors in preconditioning-induced protection has recently been described. The aims of this study were to establish whether: (i) opioid receptor stimulation acts as a trigger ( during the preconditioning protocol) or as a mediator ( during sustained ischaemia) of cardioprotection using either morphine or [D-ala(2), D-leu(5)] enkephalin (DADLE), a synthetic delta-opioid receptor agonist; ( ii) the beneficial effects of DADLE are protein kinase C ( PKC) -mediated; and (iii) inhibitory 'cross-talk' occurs between the beta-adrenergic and phosphatidylinositol pathways activated by release of endogenous catecholamines and opioids respectively during sustained ischaemia. The isolated, perfused working rat heart, subjected to 25 minutes' global ischaemia and 30 minutes' reperfusion, was used as the experimental model. The results showed that delta-opioid receptor stimulation with DADLE (10(-8) M), when administered for 3 x 5 minutes, had no effect, while when given 10 minutes before sustained ischaemia the drug significantly improved functional recovery during reperfusion. This indicates that opioid receptor stimulation acts as a mediator rather than a trigger in the protection elicited. Morphine ( 3 x 10(-7)) when administered in the same manner was without effect. Opioid receptor stimulation caused a marked reduction in the beta -adrenergic response to isoproterenol, indicating inhibitory cross-talk between the phosphatidyl-inositol and beta-adrenergic signal transduction pathways. However, reduction of the beta-adrenergic response to ischaemia does not appear to be the mechanism of opioid-induced protection, as indicated by 3',5' -cyclic adenosine monophosphate (cAMP) levels at the end of 25 minutes' global ischaemia. Opioid receptor-mediated protection against ischaemic damage is PKC-dependent, since DADLE-induced protection could be abolished by the inhibitor chelerythrine.

Adrenergic beta-Agonists↗
PubMedDate not supplied

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.

Animals↗