Protection of the ischaemic heart: investigations into the phenomenon of ischaemic preconditioning.

Exposure of the heart to one or more short episodes of ischaemia/reperfusion protects the heart against a subsequent prolonged period of ischaemia, as evidenced by a reduction in infarct size and an improvement in functional recovery during reperfusion. Elucidation of the mechanism of this endogenous protection could lead to the development of pharmacological mimetics to be used in the clinical setting. The aim of our studies was therefore to gain more information regarding the mechanism of ischaemic preconditioning, using the isolated perfused working rat heart as model. A preconditioning protocol of 1 x 5 or 3 x 5 min of ischaemia, interspersed with 5 min of reperfusion was found to protect hearts exposed to 25 min of global ischaemia or 35-45 min of regional ischaemia. These models were used throughout our studies. In view of the release of catecholamines by ischaemic tissue, our first aim was to evaluate the role of the alphaadrenergic receptor in ischaemic preconditioning. However, using a multi-cycle ischaemic preconditioning protocol, we could not find any evidence for alpha-1 adrenergic or PKC activation in the mechanism of preconditioning. Cyclic increases in the tissue cyclic nucleotides, cAMP and cGMP were found, however, to occur during a multi-cycle preconditioning protocol, suggesting roles for the beta-adrenergic signalling pathway and nitric oxide (NO) as triggers of cardioprotection. This was substantiated by the findings that (1) administration of the beta-adrenergic agonist, isoproterenol, or the NO donors SNAP or SNP before sustained ischaemia also elicited cardioprotection similar to ischaemic preconditioning; (2) beta-adrenergic blockade or nitric oxide synthase inhibition during an ischaemic preconditioning protocol abolished protection. Effectors downstream of cAMP, such as p38MAPK and CREB, were also demonstrated to be involved in the triggering process. Our next step was to evaluate intracellular signalling during sustained ischaemia and reperfusion. Our results showed that ischaemic preconditioned-induced cardioprotection was associated with a significant reduction in tissue cAMP, attenuation of p38MAPK activation and increased tissue cGMP levels and HSP27 activation, compared to non-preconditioned hearts. The role of the stress kinase p38MAPK was further investigated by using the inhibitor SB203580. Our results suggested that injury by necrosis and apoptosis share activation of p38MAPK as a common signal transduction pathway and that pharmacological targeting of this kinase offers a tenable option to manipulate both these processes during ischaemia/reperfusion injury.

The many faces of H89: a review.

H89 is marketed as a selective and potent inhibitor of protein kinase A (PKA). Since its discovery, it has been used extensively for evaluation of the role of PKA in the heart, osteoblasts, hepatocytes, smooth muscle cells, neuronal tissue, epithelial cells, etc. Despite the frequent use of H89, its mode of specific inhibition of PKA is still not completely understood. It has also been shown that H89 inhibits at least 8 other kinases, while having a relatively large number of PKA-independent effects which may seriously compromise interpretation of data. Thus, while recognizing its kinase inhibiting properties, it is advised that H89 should not be used as the single source of evidence of PKA involvement. H-89 should be used in conjunction with other PKA inhibitors, such as Rp-cAMPS or PKA analogs.

Comparison between ischaemic and anisomycin-induced preconditioning: role of p38 MAPK.

To further evaluate the significance of p38 MAPK as trigger or mediator in ischaemic preconditioning, anisomycin and SB 203580 were used to manipulate its activation status. Special attention was given to the concentration of the drugs and protocols used. The isolated perfused rat heart, subjected to either 25 min global ischaemia or 35 min regional ischaemia, was used as experimental model. This was preceded by anisomycin (2 or 5 muM: 3 x 5 min; 5 muM: 5 min or 10 min; 5 muM: 10 min + 10 min washout or 20 muM: 20 min) or SB 203580 (2 muM: 3 x 5 min; before and during 3 x 5 min or 1 x 5 min ischaemic preconditioning; 10 min). Endpoints were functional recovery during reperfusion and infarct size.Anisomycin, regardless of the protocol, reduced infarct size, but did not improve functional recovery. In a number of experiments activation of JNK by anisomycin was blocked by SP 600125 (10 muM). SP 600125 had no effect on the anisomycin-induced reduction in infarct size. SB 203580 when administered for 10 min before sustained ischaemia, improved functional recovery and reduced infarct size. SB 203580 could not abolish the beneficial effects of a multi-cycle preconditioning protocol, but it significantly reduced the outcome of 1 x 5 min preconditioning. In all hearts improved functional recovery and reduction in infarct size were associated with attenuation of p38 MAPK activation during sustained ischaemia-reperfusion. The results indicate that activation of p38 MAPK acts as a trigger of preconditioning, while attenuation of its activation is a prerequisite for improved recovery and a reduction in infarct size.

Ischemic preconditioning: infarct size is a more reliable endpoint than functional recovery.

The search for the mechanism of preconditioning-induced cardioprotection has been hampered by controversial results obtained by workers using different animal species, experimental models, protocols and endpoints. The aim of this study was to evaluate the role of the perfusion model (retrograde vs working), the infarct size and severity of ischaemia (regional vs global) as well as the endpoint (functional recovery vs infarct size) in preconditioning. The isolated perfused rat heart was preconditioned by 3 x 5 min global ischaemia, followed by different periods of regional or global ischaemia and reperfusion. Ischaemic preconditioning of working hearts resulted in increased functional recovery after 25-35 min global ischaemia, while retrogradely perfused hearts showed no significant improvement (except after 30 min global ischaemia). In addition, the percentage reduction in functional performance during reperfusion observed in the latter group was significantly less than in working hearts. Hearts were also subjected to regional ischaemia, perfused in either retrograde or working mode and infarct size determined. Regionally ischaemic working as well as retrogradely perfused hearts when preconditioned showed a significant increase in functional recovery after 35 min ischaemia only. In contrast to global ischaemia, the percentage recovery in mechanical performance of regionally ischaemic hearts was not affected by the mode of perfusion. Preconditioning of working hearts caused a significant reduction in infarct size after both 30 and 35 min ischaemia. However, preconditioned retrogradely perfused hearts showed a significant decline in infarct size after 35 min regional ischaemia only. In conclusion, the effect of the perfusion mode on functional recovery is dependent on the size and severity of ischaemia. It also affects the ischaemic time at which infarct size reduction by prior preconditioning occurs in the retrogradely perfused heart.

Thyroid hormone and the heart.

Thyroid hormone has important cardiovascular effects, and abnormalities of its production cause cardiovascular morbidity. The role of both excessive and insufficient thyroid hormone production in the pathogenesis of clinical cardiac diseases can be deduced from thyroid hormone-induced molecular changes. Thyroid hormone regulates the expression of myocardial genes regulating the handling of calcium, which affects both systolic and diastolic myocardial function. Thyroid hormone also has indirect and direct effects on peripheral vascular smooth muscle tone, and alters the coupling of the left ventricle and arterial system. Excessive production of thyroid hormone results in an increased cardiac output as well as increased cardiac work efficiency, but reduced cardiac reserve. Amiodarone therapy for cardiac rhythm can cause both hyper- and hypothyroidism. Amiodarone-induced thyrotoxicosis (AIT) can be due to either excessive thyroid hormone production (type I AIT) or thyroid hormone release due to an inflammatory condition (type II AIT). Classification of AIT is helpful in guiding therapy. Amiodarone causes changes in the thyroid function tests of euthyroid patients on therapy--it inhibits the conversion of T(4) and T(3), which results in decreased T(3) and slightly increased T(4) serum levels in euthyroid patients. Baseline thyroid functions should therefore be determined before starting amiodarone therapy, and at 6-monthly intervals thereafter.

p38 MAPK activation triggers pharmacologically-induced beta-adrenergic preconditioning, but not ischaemic preconditioning.

p38 Mitogen-activated protein kinase (p38 MAPK) is activated by short episodes of ischaemia-reperfusion as well as by sustained ischemia followed by reperfusion, Whether activation of this kinase is beneficial or deleterious to the ischaemic heart is still a subject of controversy. Since transient beta-adrenergic stimulation (5 min) stimulates p38 MAPK activation and mimics the cardioprotection of ischaemic preconditioning, it was used as a tool to further evaluate the role of this kinase in cardioprotection. The isolated perfused working rat heart, subjected to 25 min ischaemia and 30 min reperfusion was used as experimental model. p38 MAPK and ATF2 activation was determined using Western blots. The results showed that isoproterenol stimulated p38 MAPK in a dose- and time-dependent manner. Ischaemia-induced activation of p38 MAPK could be partially abolished by beta- and alpha1-adrenergic receptor blockade. Isoproterenol activation of the kinase could be abolished by alprenolol and verapamil, but not by 8-cyclopentyladenosine. p38 MAPK activation induced by either a multi-episode preconditioning protocol or isoproterenol (10(-7) M for 5 min) was associated with a significant reduction in p38 MAPK activation at all time intervals studied during 25 min global ischaemia and at 20 and 30 min of reperfusion, compared with the marked activation observed in untreated non-preconditioned hearts. In each case attenuation of p38 MAPK activation during ischaemia and during reperfusion was associated with improved functional recovery during reperfusion. Cyclic elevations in tissue cAMP during an ischaemic preconditioning protocol acted as trigger of cardioprotection, since pretreatment of such hearts with alprenolol abolished cardioprotection. Mechanical failure in such hearts was characterized by a significant stimulation of p38 MAPK activity during ischaemia and reperfusion. However, p38 MAPK activation during an ischaemic preconditioning protocol did not act as trigger: inhibition of p38 MAPK activation by SB 203580 during the preconditioning phase did not abolish cardioprotection. In fact, functional recovery was significantly better than that of untreated preconditioned hearts. On the other hand, SB 203580, when administered before and during the isoproterenol-preconditioning protocol abolished cardioprotection, suggesting that p38 MAPK activation by a beta -adrenergic-induced preconditioning protocol does act as trigger of cardioprotection. In addition, attenuation of p38 MAPK activity during sustained ischaemia and reperfusion as occurs in ischaemic- or isoproterenol-preconditioned hearts, is beneficial.

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.

Activation of p38 MAPK induced by a multi-cycle ischaemic preconditioning protocol is associated with attenuated p38 MAPK activity during sustained ischaemia and reperfusion.

The role of p38 mitogen-activated protein kinase (MAPK) in ischaemic preconditioning remains controversial. Since most previous studies focussed on events only during sustained ischaemia, the aim of this study was to establish the activation pattern of p38 MAPK during a multicycle preconditioning protocol, sustained ischaemia as well as reperfusion and to correlate these events with functional recovery of the isolated perfused rat heart. Isolated perfused rat hearts were preconditioned by 3x5 min global ischaemia followed by 25 min global ischaemia and 30 min reperfusion. Non-preconditioned hearts were subjected to 25 min global ischaemia and 30 min reperfusion. Hearts were freeze-clamped and p38 MAPK activation in tissue lysates was assessed by standard Western blotting techniques, using a dual phospho-p38 MAPK antibody as well as a non-radioactive IP-kinase assay. The results showed that transient dual phosphorylation and activation of p38 MAPK occurs during a 3x5 min preconditioning protocol: the activation was maximal during the first episode, becoming progressively lower during the second and third episodes. p38 MAPK activation was significantly less during both sustained ischaemia and reperfusion in preconditioned hearts, when compared with non-preconditioned hearts. Attenuation of p38 MAPK activity during sustained ischaemia and reperfusion was associated with improved functional recovery. The effect of inhibition of p38 MAPK activation on cardioprotection was further evaluated in adult, isolated cardiomyocytes. Administration of SB 203580 (1-10 microM) before and during the preconditioning protocol, had no effect on cell morphology and viability after 2 h hypoxia, compared to untreated preconditioned cardiomyocytes. When administered to non-preconditioned cells before the onset of 2 h hypoxia, it caused a significant improvement in both morphology and viability. In summary, the results suggest that attenuation of the kinase activity during sustained ischaemia and reperfusion may be an essential element of the preconditioning process.

Nitric oxide: a trigger for classic preconditioning?

To determine whether nitric oxide (NO) is involved in classic preconditioning (PC), the effect of NO donors as well as inhibition of the L-arginine-NO-cGMP pathway were evaluated on 1) the functional recovery during reperfusion of ischemic rat hearts and 2) cyclic nucleotides during both the PC protocol and sustained ischemia. Tissue cyclic nucleotides were manipulated with NO donors [S-nitroso-N-penicillamine (SNAP), sodium nitroprusside (SNP), or L-arginine] and inhibitors of nitric oxide synthase (N(omega)-nitro-L-arginine methyl ester or N-nitro-L-arginine) or guanylyl cyclase (1H-[1,2,4]oxadiazolol-[4,3-a]quinoxaline-1-one). Pharmacological elevation in tissue cGMP levels by SNAP or SNP before sustained ischemia elicited functional improvement during reperfusion comparable to that by PC. Administration of inhibitors before and during the PC protocol partially attenuated functional recovery, whereas they had no effect when given after the ischemic PC protocol and before sustained ischemia only, indicating a role for NO as a trigger but not as a mediator. Ischemic PC, SNAP, or SNP caused a significant increase in cGMP and a reduction in cAMP levels after 25 min of sustained ischemia that may contribute to the protection obtained. The results obtained suggest a role for NO (and cGMP) as a trigger in classic PC.

A newly created splice donor site in exon 25 of the MyBP-C gene is responsible for inherited hypertrophic cardiomyopathy with incomplete disease penetrance.

BACKGROUND: Hypertrophic cardiomyopathy is a myocardial disorder resulting from inherited sarcomeric dysfunction. We report a mutation in the myosin-binding protein-C (MyBP-C) gene, its clinical consequences in a large family, and myocardial tissue findings that may provide insight into the mechanism of disease. METHODS AND RESULTS: History and clinical status (examination, ECG, and echocardiography) were assessed in 49 members of a multigeneration family. Linkage analysis implicated the MyBP-C gene on chromosome 11. Myocardial mRNA, genomic MyBP-C DNA, and the myocardial proteins of patients and healthy relatives were analyzed. A single guanine nucleotide insertion in exon 25 of the MyBP-C gene resulted in the loss of 40 bases in abnormally processed mRNA. A 30-kDa truncation at the C-terminus of the protein was predicted, but a polypeptide of the expected size ( approximately 95 kDa) was not detected by immunoblot testing. The disease phenotype in this family was characterized in detail: only 10 of 27 gene carriers fulfilled diagnostic criteria. Five carriers showed borderline hypertrophic cardiomyopathy, and 12 carriers were asymptomatic, with normal ECG and echocardiograms. The age of onset in symptomatic patients was late (29 to 68 years). In 2 patients, outflow obstruction required surgery. Two family members experienced premature sudden cardiac death, but survival at 50 years was 95%. CONCLUSIONS: Penetrance of this mutation was incomplete and age-dependent. The large number of asymptomatic carriers and the good prognosis support the interpretation of benign disease.

Ischemic preconditioning and the beta-adrenergic signal transduction pathway.

BACKGROUND: Previous studies from our laboratory showed cyclic increases in tissue cAMP during a multiple-cycle preconditioning (PC) protocol, followed by attenuated cAMP accumulation during sustained ischemia. The aim of this study was to determine whether ischemia-induced activation of the beta-adrenergic signaling pathway could act as a trigger in eliciting protection. METHODS AND RESULTS: Isolated perfused rat hearts were preconditioned by 3x5 minutes of global ischemia, interspersed by 5 minutes of reperfusion. beta-Adrenergic responsivity was assessed by measurement of tissue cAMP generation after beta-adrenergic agonist administration at the end of the PC protocol. Tissue cAMP, adenylyl cyclase, and protein kinase A (PKA) activities and beta-adrenergic receptor characteristics were assessed at different times. The role of cAMP generation in eliciting PC was studied by investigation of functional recovery during reperfusion after 25 minutes of global ischemia after (1) cAMP increases in the trigger period were prevented with the beta-adrenergic blocker alprenolol 7.5x10(-5) mol/L and (2) increases in cAMP were elicited by administration of forskolin 10(-7) and 10(-6) mol/L or isoproterenol 10(-8), 10(-7), and 10(-6) mol/L. Intermittent ischemia resulted in reduced beta-adrenergic responsivity at the end of the protocol, although B(max) and K(d) values of the beta-adrenergic receptor population and adenylyl cyclase and PKA activities were increased. Abolishment of cyclic increases in cAMP before sustained ischemia attenuated myocardial protection against ischemia, whereas agonists elicited protection. No clear correlation between protection and beta-adrenergic desensitization was observed. CONCLUSIONS: Ischemia-induced activation of the beta-adrenergic signaling pathway during preconditioning should also be considered a trigger in eliciting preconditioning.

Ischaemic preconditioning does not protect hypertrophied myocardium against ischaemia.

OBJECTIVES: Because ischaemic preconditioning elicits a potent endogenous protective mechanism against the development of myocardial infarction, it is important to explore its utilisation in clinical situations. The aim of this study was to examine whether the myocardium of rats with genetic hypertension could be protected by ischaemic preconditioning. METHODS: Male New Zealand genetically hypertensive rats (GH-Wistar-derived) and normotensive Wistar controls (WAG-Wistar-derived), aged 12 months, were used. Isolated perfused hearts were preconditioned by 3 periods of 5 minutes' global ischaemia, interspersed with 5 minutes' reperfusion, and subsequently subjected to 25 minutes' global ischaemia, followed by 30 minutes' reperfusion. RESULTS: Heart and body mass were significantly higher in GH rats. Although the heart/body mass ratios of GH rats were higher than those of WAG rats, the difference was not significant. The reperfusion coronary flow pattern during the preconditioning protocol differed markedly between the 2 groups. Only normotensive WAG hearts demonstrated protective effects of preconditioning on post-ischaemic function and tissue creatine phosphate content, while the GH hearts could not be preconditioned. CONCLUSIONS: An explanation for the failure of preconditioning in GH hearts is not yet available. The data caution against implementation of preconditioning in patients with angina pectoris and left ventricular hypertrophy.

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.

No evidence for mediation of ischemic preconditioning by alpha 1-adrenergic signal transduction pathway or protein kinase C in the isolated rat heart.

The purpose of this study was to elucidate the role of activation of the alpha 1-adrenergic signal transduction pathway and of protein kinase C (PKC) in the mechanism of protection of functional recovery by ischemic preconditioning in the isolated perfused rat heart. After a stabilization period, nonpreconditioned and preconditioned isolated perfused rat hearts were subjected to sustained ischemia for 25 and 30 minutes of reperfusion. Preconditioning consisted of three episodes of 5 minutes of ischemia, interspersed with 5 minutes of reperfusion. The endpoint was postischemic functional recovery. The effectiveness of preconditioning in the presence of the alpha 1-adrenergic blocker prazosin, the selective PKC blockers chelerythrine and bisindolylmaleimide (BIM), and the ability of repetitive alpha 1-adrenergic activation to mimic preconditioning were compared with the appropriate nonpreconditioned and preconditioned control groups. Alpha 1-adrenergic blockade with prazosin (3 x 10(-7) M) during the preconditioning phase did not abolish the protective effect of preconditioning on functional recovery, and repeated intermittent alpha 1-adrenergic activation with phenylephrine in different concentrations (1 x 10(-8) to 3 x 10(-5) M) did not mimic the protective effect of preconditioning. PKC blockade with the selective PKC inhibitors, chelerythrine (10 microM) and BIM (4 microM), did not abolish the protective effect of preconditioning on functional recovery is isolated perfused rat hearts when given either during the preconditioning phase or shortly before the onset of sustained ischemia. The characteristic metabolic changes of preconditioning during sustained ischemia, namely, energy sparing as manifested in reduced accumulation of lactate, were also not abolished by preconditioning in the presence of selective PKC blockers. We conclude that no evidence could be found for alpha 1-adrenergic or PKC activation in the mechanism of ischemic preconditioning in the isolated rat heart.

Preconditioning with a single short episode of global ischemia in the isolated working rat heart: effect on structure, mechanical function, and energy metabolism for various durations of sustained global ischemia.

PURPOSE: Preconditioning in the setting of global ischemia, using functional recovery during reperfusion as the endpoint, has recently been demonstrated in the isolated perfused rat heart. It has been suggested that its beneficial actions have a metabolic basis. The isolated rat heart has not been fully characterized with respect to the metabolic, functional, and structural changes associated with this phenomenon in the setting of global ischemia. The purpose of this study was to determine (1) the time course of protection conferred by a single episode (5 minutes) of preconditioning; (2) changes in tissue high energy phosphates, lactate, and glycogen levels at different time intervals; and (3) morphological appearance of the heart at the end of ischemia as well as after reperfusion. METHODS: Isolated perfused working rat hearts were used. Preconditioning consisted of a single episode of 5 minutes of global ischemia and 15 minutes of reperfusion. Preconditioned and non-preconditioned hearts were subjected to global ischemia of 20-35 minutes duration. Functional recovery, energy metabolism (high energy phosphates, lactate, and glycogen), and structural appearance were studied at different stages. RESULTS: The functional recovery of the preconditioned hearts was significantly higher than in the corresponding nonpreconditioned group during reperfusion for all durations of ischemia longer than 25 minutes. The degree of protection observed was less than reported previously. A minor degree of energy sparing was reflected by differences in the rate of depletion of glycogen and accumulation of tissue lactate during the sustained episode of ischemia. Semiquantitative light microscopy evaluation revealed that ischemia-induced structural damage was less in the preconditioned hearts, both at the end of the sustained ischemic episode as well as after reperfusion. CONCLUSIONS: A single episode of global ischemia successfully preconditions the isolated working rat heart. The protection elicited was demonstrated on a functional and structural level, and was accompanied by a small energy-sparing effect.

Organophosphate and carbamate poisoning.

Organophosphate insecticides may cause serious poisoning either accidentally or by deliberate ingestion. Toxic symptoms are produced by acetylcholine accumulation at cholinergic receptors. Diagnosis is based on history of exposure or ingestion, symptoms and signs of cholinergic overactivity and a decrease in serum pseudocholinesterase levels. Following diagnosis, grading of disease severity may identify patients with serious poisoning who should receive treatment in intensive care using adequate doses of anticholinergic drugs. Complications, particularly ventricular arrhythmias, central nervous system depression or seizures, and respiratory failure, should be anticipated and treated. Relapse may occur after seemingly successful treatment. Public education with regard to symptoms of toxicity must be encouraged, and physicians must provide skilled treatment for a potentially lethal condition.

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.

Cyclosporin as a treatment for interstitial lung disease of unknown aetiology.

Ten patients with progressive, symptomatic interstitial lung disease of unknown aetiology who were treated with cyclosporin A were reviewed. Five had clinical and histopathological features of cryptogenic fibrosing alveolitis and five a progressive restrictive lung disease characterised by interstitial infiltration with lymphocytes and minimal fibrosis, which could not be classified precisely. Three patients with lymphocytic infiltration showed a response to initial treatment with cyclosporin A alone at high dosage, but toxicity precluded further treatment. All 10 patients then received low doses of cyclosporin A and prednisone. Three of the patients with cryptogenic fibrosing alveolitis and all five patients with lymphocytic infiltration responded with a reduction in dyspnoea or an increase in vital capacity, or both; cyclosporin A appeared to be effective, or at least to have a corticosteroid potentiating effect. A high incidence of side effects occurred, though these do not necessarily prohibit the long term use of cyclosporin A when it is indicated clinically. Cyclosporin A may be effective in the treatment of interstitial lung disease of unknown aetiology. Further studies are required to determine the long term outcome of treatment.