Preischemic Treatment Research Articles

KB-R7943, a selective Na+/Ca2+ exchange inhibitor, protects against ischemic acute renal failure in mice by inhibiting renal endothelin-1 overproduction.

We investigated whether the preischemic or postischemic treatment with KB-R7943, a novel and selective Na+/Ca2+ exchange inhibitor, has renal protective effects in mice with ischemic acute renal failure (ARF). Ischemic ARF was induced by clamping the left renal pedicle for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was markedly diminished 24 h after reperfusion. Preischemic treatment with KB-R7943 attenuated the ARF-induced renal dysfunction. The ischemia/reperfusion-induced renal dysfunction was also overcome by postischemic treatment with KB-R7943. Histopathologic examination of the kidneys of ARF mice revealed severe renal damage such as tubular necrosis, proteinaceous casts in tubuli, and medullary congestion. Histologically evident damage and Ca2+ deposition in necrotic tubular epithelium were improved by preischemic treatment with KB-R7943. In addition, preischemic treatment with KB-R7943 significantly suppressed the increment of endothelin-1 (ET-1) content in the kidney at 2, 6, and 24 h after reperfusion. These findings suggest that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by renal ET-1 overproduction, plays an important role in the pathogenesis of the ischemia/reperfusion-induced ARF. KB-R7943 may prove to be an effective therapeutic agent for cases of ischemic ARF in humans.

The time course of acquisition of ischemic tolerance and induction of heat shock protein 70 after a brief period of ischemia in the spinal cord in rabbits.

We examined the time course of development of ischemic tolerance in the spinal cord and sought its mechanism exploring the expression of heat shock protein 70 (HSP70). Spinal cord ischemia was produced in rabbits by occlusion of the abdominal aorta. In Experiment 1, neurologic and histopathologic outcome was evaluated 48 h after prolonged ischemia (20 min) that was given 2 days, 4 days, or 7 days after a short period of ischemia (ischemic pretreatment) sufficient to abolish postsynaptic component of spinal cord evoked potentials. Control animals were given prolonged ischemia 4 days after sham operation. In Experiment 2, HSP70 expression in motor neurons after pretreatment without exposure to prolonged ischemia was examined by immunohistochemical staining. Ischemic pretreatment 4 days (but not 2 days or 7 days) before 20 min ischemia exhibited protective effects against spinal cord injury. In the cytoplasm, HSP70 immunoreactivity was mildly increased after 2, 4, and 7 days of ischemic pretreatment. However, the incidence of nuclear HSP70 immunoreactivity 2 days, 4 days, and 7 days after ischemic pretreatment was 2 of 6 animals, 4 of 6 animals, and 1 of 6 animals, respectively (none in the control group). These results suggest that ischemic tolerance is apparent 4 days after ischemic pretreatment and that HSP70 immunoreactivity in the nucleus may provide some insight into the mechanisms of ischemic tolerance in the spinal cord.

Can isoflurane mimic ischaemic preconditioning in isolated rat heart?

Ischaemic preconditioning can protect the myocardium against ischaemic injury by opening of the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel. Isoflurane is also thought to open this channel. The present investigation tested the hypothesis that pre-ischaemic treatment with isoflurane mimics ischaemic preconditioning (producing chemical preconditioning) and thereby protects the myocardium against ischaemic injury in an isolated rat heart model. Control hearts underwent 30 min of global no-flow ischaemia followed by 60 min of reperfusion. The hearts of the preconditioning group underwent two 5 min periods of no-flow ischaemia interspersed with 5 min of reperfusion before the sustained ischaemia. In three additional groups, hearts were subjected to 15 min of 1.5 minimal alveolar concentration (MAC) of isoflurane (ISO-1), 15 min 3 MAC (ISO-2) or 25 min 1.5 MAC (ISO-3) of isoflurane followed by 5 min washout before the global ischaemia. Left ventricular (LV) developed pressure and creatine kinase release were measured as variables of myocardial performance and cellular injury, respectively. Recovery of LV developed pressure was improved after ischaemic preconditioning [after 60 min reperfusion, mean 63 (SEM 6)% of baseline] compared with the control group [18 (4)% P<0.01] but not by isoflurane, independently of concentration or duration of administration [ISO-1, 17 (2)%, P=0.99 vs control; ISO-2, 12 (3)%, P=0.64; ISO-3, 4 (1)%, P=0.06]. Total creatine kinase release over 1 h of reperfusion was not significantly different between control [251 (36) U g(-1) dry weight] and all isoflurane groups [ISO-1, 346 (24) U g(-1), P=0.30; ISO-2, 313 (33) U g(-1), P=0.73; ISO-3, 407 (40) U g(-1), P=0.03]. These results indicate that pre-ischaemic administration of isoflurane does not cause anaesthetic-induced preconditioning in the isolated rat heart.

Combination of N-methyl-1-deoxynojirimycin and ischemic preconditioning markedly reduces the size of myocardial infarcts in rabbits.

N-methyl-1-deoxynojirimycin (NMDN), an a-glucosidase inhibitor, reduces myocardial infarct size by reducing the glycogenolytic rate through inhibition of the alpha-1,6-glucosidase of glycogen-debranching enzyme in the heart, in addition to possessing an antihyperglycemic action by blocking alpha-1,4-glucosidase in the intestine. Ischemic preconditioning (PC), which markedly reduces the size of the myocardial infarct, is known to reduce the activity of phosphorylase and reduce the glycogenolytic rate. Therefore, it was hypothesized that a combination of pharmacological inhibition of glycogenolysis by an alpha-1,6-glucosidase inhibitor, NMDN, and PC could markedly reduce myocardial infarct size more than NMDN or PC alone. Japanese white rabbits without collateral circulation were subjected to a 30-min coronary occlusion followed by 48-h reperfusion. The infarct sizes as a percentage of area at risk were significantly reduced by pre-ischemic treatment with either 100mg/kg of NMDN or PC of 5 min ischemia and 5 min reperfusion alone (15.9+/-2.0%, n=8, and 10.3+/-1.2%, n=8, respectively) as compared with the control (43.9+/-2.2%, n=8). However, the combination of 100mg/kg of NMDN and PC significantly reduced the infarct size (4.9+/-1.2, n=8) compared with NMDN or PC alone. Another 40 rabbits, also given 100mg of NMDN, PC, NMDN+PC or saline before ischemia (n=10 in each group), were killed for biochemical analysis after 30 min of ischemia. NMDN and PC preserved the glycogen content and attenuated the lactate accumulation, respectively, as compared with the control. However, the combination of NMDN and PC preserved significantly more glycogen and significantly reduced lactate accumulation than either NMDN or PC alone. The combination of NMDN and PC markedly reduced the myocardial infarct size more than either process alone. The marked preservation of glycogen and marked attenuation of lactate accumulation by the combination of NMDN and PC suggest that the mechanism for this effect of NMDN+PC is related to the inhibition of glycogenolysis.

N-methyl-1-deoxynojirimycin (MOR-14), an alpha-glucosidase inhibitor, markedly improves postischemic left ventricular dysfunction.

We examined whether pharmacological inhibition of glycogenolysis by N-methyl-1-deoxynojirimycin (MOR-14), a new compound which reduces the glycogenolytic rate by inhibiting the alpha-1,6-glucosidase activity of the glycogen-debranching enzyme, can protect the heart against postischemic left ventricular dysfunction. The hearts of male Sprague-Dawley rats were excised, and perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O2 and 5% CO2. The hearts were paced at 320 beats/min except during the ischemia. Left ventricular developed pressure (LVDP, mmHg), +/-dP/dt (mmHg/s), and coronary flow (ml/min) were continuously monitored. All hearts were perfused for a total of 120 min including a 30-min preischemic period followed by a 30-min episode of global ischemia and 60 min reperfusion. with or without 0.5 or 2 mM of MOR-14 during the 30-min preischemic period or the first 30 min of reperfusion. In another series of experiments, the myocardial content of glycogen and lactate was measured during the 30-min episode of ischemia in groups treated with and without 2mM of MOR-14. Preischemic but not postischemic treatment with MOR-14 significantly improved LVDP and +/-dP/dt without altering coronary flow during reperfusion in a dose-dependent manner. MOR-14 significantly preserved the glycogen content and significantly attenuated the lactate accumulation during the 30-min episode of ischemia. Preischemic treatment with MOR-14 is protective against postischemic left ventricular dysfunction through the inhibition of glycogenolysis in the isolated rat heart.

Cardioprotection with kappa-opioid receptor stimulation is associated with a slowing of cross-bridge cycling.

Opioid and alpha-adrenergic receptor activation protect the heart from ischemic damage. One possible intracellular mechanism to explain this is that an improvement in ATP availability contributes to cardioprotection. We tested this hypothesis by correlating postischemic left ventricular developed pressure (LVDP) and myofibrillar Ca(2+)-dependent actomyosin Mg(2+)-ATPase from isolated rat hearts treated with the kappa-opioid receptor agonist U-50488H (1 microM) or the alpha-adrenergic receptor agonist phenylephrine (10 microM) + propranolol (3 microM). Preischemic treatment with U-50488H or phenylephrine + propranolol improved postischemic LVDP recovery by 25-30% over control hearts. Ca(2+)-dependent actomyosin Mg(2+)-ATPase was found to be 20% lower in both U-50488H- and phenylephrine + propranolol-treated hearts compared with control hearts. The kappa-opioid receptor antagonist nor-binaltorphimine (1 microM) abolished the effects of U-50488H on postischemic LVDP and actomyosin Mg(2+)-ATPase activity. Reduced actomyosin ATP utilization was also suggested in single ventricular myocytes treated with either U-50488H or the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), because U-50488H and PMA lowered maximum velocity of unloaded shortening by 15-25% in myocytes. U-50488H and phenylephrine + propranolol treatment both resulted in increased phosphorylation of troponin I and C protein. These findings are consistent with the hypothesis that kappa-opioid and alpha-adrenergic receptors decrease actin-myosin cycling rate, leading to a conservation of ATP and cardioprotection during ischemia.

Effect of ischemic pretreatment on heat shock protein 72, neurologic outcome, and histopathologic outcome in a rabbit model of spinal cord ischemia

Objective: In the present study, we investigated the effect of ischemic pretreatment on heat shock protein 72 concentration and neurologic and histopathologic outcome after transient spinal cord ischemia. Methods: In 28 New Zealand White rabbits, an aortic occlusion device was placed infrarenally. The animals were randomly assigned to 2 groups: ischemic pretreatment (n = 14 animals) and control (n = 14 animals). The duration of ischemic pretreatment was 6 minutes. After 24 hours, the aorta was occluded for 26 minutes in both groups of animals. Neurologic function was assessed 24 and 48 hours after the definite ischemic insult. At 48 hours, the animals were killed for histopathologic evaluation of the spinal cord. In a separate set of animals, heat shock protein 72 levels were determined in the lumbar spinal cord after both a 6- and 10-minute ischemic period, with the use of a Western blot analysis. Results: No significant difference in neurologic outcome between the groups was observed at 24 and 48 hours. The incidence of paraplegia and severe paresis at 48 hours was 79% in the control group and 92% in the ischemic pretreatment group. There was no difference in histopathologic scores between the groups. Heat shock protein 72 could be clearly detected 1 and 2 days after 6- or 10-minute periods of spinal cord ischemia. Conclusions: In the present rabbit study, ischemic pretreatment could not induce tolerance against a moderately severe spinal cord ischemic insult, despite increased heat shock protein 72 levels after the preconditioning stimulus. (J Thorac Cardiovasc Surg 2000;120:513-9)

Role of Endothelial Nitric Oxide Generation and Peroxynitrite Formation in Reperfusion Injury After Focal Cerebral Ischemia

Reperfusion injury is one of the factors that unfavorably affects stroke outcome and shortens the window of opportunity for thrombolysis. Surges of nitric oxide (NO) and superoxide generation on reperfusion have been demonstrated. Concomitant generation of these radicals can lead to formation of the strong oxidant peroxynitrite during reperfusion. We have examined the role of NO generation and peroxynitrite formation on reperfusion injury in a mouse model of middle cerebral artery occlusion (2 hours) and reperfusion (22 hours). The infarct volume was assessed by 2,3,5-triphenyl tetrazolium chloride staining; blood-brain barrier permeability was evaluated by Evans blue extravasation. Nitrotyrosine formation and matrix metalloproteinase-9 expression were detected by immunohistochemistry. Infarct volume was significantly decreased (47%) in animals treated with the nonselective nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NA) at reperfusion. The specific inhibitor of neuronal NOS, 7-nitroindazole (7-NI), given at reperfusion, showed no protection, although preischemic treatment with 7-NI decreased infarct volume by 40%. Interestingly, prereperfusion administration of both NOS inhibitors decreased tyrosine nitration (a marker of peroxynitrite toxicity) in the ischemic area. L-NA treatment also significantly reduced vascular damage, as indicated by decreased Evans blue extravasation and matrix metalloproteinase-9 expression. These data support the hypothesis that in addition to the detrimental action of NO formed by neuronal NOS during ischemia, NO generation at reperfusion plays a significant role in reperfusion injury, possibly through peroxynitrite formation. Contrary to L-NA, failure of 7-NI to protect against reperfusion injury suggests that the source of NO is the cerebrovascular compartment.

Reduced glutathione oxidation ratio and 8 ohdG accumulation by mild ischemic pretreatment

A critical role of oxidative stress has been implicated in ischemic brain damage. Mild ischemic pretreatment and/or synthesis of heat shock proteins (HSPs) has been suggested to protect against oxidative brain damage. However, experimental support of this suggestion have proven to be difficult partly because sensitive indices to assess oxidative consequences of ischemic brain damage were few. In this study, we have attempted to establish biochemical assay systems to quantitate oxidative brain damage following ischemia. We produced experimental brain ischemia in the Mongolian gerbil ( Meriones unguiculatus) and examined the hippocampus for ischemic brain damage. The results obtained from ischemic gerbil hippocampus demonstrated that oxidative brain damage can be quantitated by determining glutathione oxidation ratio together with the accumulation of the oxidative DNA damage product, 8-hydroxy-2′-deoxyguanosine (8 ohdG). Our results also demonstrated a role for mild ischemic pretreatment and synthesis of HSPs against oxidative brain damage. We showed that mild 2-min ischemic pretreatment reduced the degree of both glutathione oxidation ratio and 8 ohdG accumulation in gerbil hippocampus subsequent to 10 min ischemic challenge. We also showed that the accumulation of HSP70 was closely associated with the reduction of oxidative brain damage. To our knowledge, this is the first report to investigate glutathione redox states and oxidative DNA damage levels to evaluate a protective role of mild ischemic pretreatment and HSP synthesis following brain ischemia. Our data validate the previous suggestions and provide new additional data that argue for the protective role of mild ischemic pretreatment and HSP70 synthesis against oxidative brain damage.

Caspase inhibitors reduce neuronal injury after focal but not global cerebral ischemia in rats.

Studies show that blocking the activation of caspases by the caspase inhibitors z-VAD.FMK and z-DEVD.FMK can reduce ischemic neuronal injury after cerebral ischemia. Because the severity of ischemia was mild in some studies, we tested the efficacy of these caspase inhibitors on moderately severe but transient forebrain and focal ischemic insults in the rat. Various regimens of z-VAD, z-DEVD, and control DMSO were given to rats subjected to either 4-vessel occlusion ischemia (4-VO, 10-minute occlusion, 7-day survival) or distal middle cerebral artery occlusion (MCAo, 90-minute occlusion, 22.5-hour survival). In global ischemia, treatments were given immediately after ischemia (experiment 1) or as preischemic and postischemic treatments (experiment 2). Three focal ischemia experiments were done. Injection times were 60 minutes into ischemia (experiment 1) and 60 minutes into ischemia plus 30 and 120 minutes after ischemia (experiment 2). Experiment 3 was identical to experiment 2 except that a 30-minute preischemia treatment was instituted. Core normothermia was maintained in all experiments during ischemia. However, in the last focal and global experiments, core and brain temperatures, respectively, were also measured after ischemia with telemetry probes. Because hyperthermia accompanied z-DEVD treatment, an extra z-DEVD-treated group (MCAo) was included with temperature clamped at normothermia. Neither z-VAD nor z-DEVD significantly reduced CA1 injury after global ischemia. In focal ischemia, both drugs significantly reduced infarction, but only in the third experiment, and the prevention of hyperthermia that accompanied z-DEVD treatment did not alter this. These results suggest a detrimental role of caspases in moderately severe focal but not global cerebral ischemia.

A novel anti-diabetic drug, miglitol, markedly reduces myocardial infarct size in rabbits.

1. We examined whether N-hydroxyethyl-1-deoxynojirimycin (miglitol), a new human anti-diabetic drug with effects to inhibit alpha-1, 6-glucosidase glycogen debranching enzyme and reduce the glycogenolytic rate as well as to inhibit alpha-1,4-glucosidase, could reduce infarct size in the rabbit heart. Rabbits were subjected to 30-min coronary occlusion followed by 48-h reperfusion. 2. The infarct size as a percentage of area at risk was not reduced by pre-ischaemic treatment with 1 mg kg(-1) miglitol (42.7+/-4.0%, n=10) compared with the saline control group (41.7+/-2.3%, n=10). However, it was significantly and dose-dependently reduced by pre-ischaemic treatment with 5 or 10 mg kg(-1) of miglitol (25.7+/-4. 5%, n=10, and 14.6+/-2.4%, n=10, respectively) without altering the blood pressure, heart rate or blood glucose level. However, there was no evidence of an infarct-size reducing effect after pre-reperfusion treatment with 10 mg kg(-1) of miglitol (35.0+/-3.0%, n=10). 3. Another 40 rabbits given 1, 5 and 10 mg kg(-1) of miglitol or saline before ischaemia (n=10 in each) were sacrificed at 30 min of ischaemia for biochemical analysis. Miglitol preserved significantly the glycogen content, and attenuated significantly the lactate accumulation in a dose dependent manner in the ischaemic region at 30 min of ischaemia. 4. Pre-ischaemic treatment, but not pre-reperfusion treatment, with miglitol markedly reduced the myocardial infarct size, independently of blood pressure and heart rate. A dose-dependent effect of miglitol on infarct size, glycogenolysis and lactate formation suggests that the mechanism may be related to the inhibition of glycogenolysis. Thus, miglitol may be beneficial for coronary heart disease as well as diabetes mellitus.

Metyrapone alleviates ischemic neuronal damage in the gerbil hippocampus

Transient forebrain ischemia was induced in gerbils, and the effect of a pre-ischemic treatment with metyrapone (100 mg/kg) on delayed neuronal death in hippocampal CA1 neurons was evaluated. The effect of metyrapone on the ischemic release of amino acids in the CA1 region was also examined by microdialysis. Hippocampal slices were used for the evaluation of the hypoxia-induced intracellular Ca 2+ increase by microfluorometry. The metyrapone treatment morphologically improved the damage provoked by 3 min of ischemia, although it did not alleviate the damage by 5 min. Ischemia for 3 min produced a 306% increase in the glutamate concentration in perfusates, and metyrapone suppressed the peak value to 42% of that in the control group. The extent of the increase in fluorescence intensity by intracellular Ca 2+ was lower by 16% in slices from metyrapone-treated animals than in controls 600 s after induction of hypoxia. The removal of Ca 2+ from the perfusion medium suppressed the hypoxic Ca 2+ increase, and the increase was further reduced in slices pretreated with metyrapone. The increase in the level of endogenous glucocorticoids, which occurs in cerebral ischemia, may aggravate ischemic neuronal damage.

Neuroprotection in ischemia of the retina in an animal model

The NMDA-receptorantagonist memantin is neuroprotective in retinal ischemia. Does this also apply to the NMDA-receptorantagonist cerestat and the glutamate release inhibitor riluzole? In 50 rats ischemia was induced by elevating the IOP of one eye to 120 mmHg for 1 h. The drugs were injected before ischemia because, according to our hypothesis, a neuroprotective effect would be most evident in prophylactic preischemia treatment. Ten rats received 20 mg/kg/d memantine s.c., 10 received 16.8 mg/kg/d cerestat s.c., 10 received 16 mg/kg/d riluzole i.p. and 20 rats served as controls. Two weeks later, the ischemic damage was histologically quantified by counting the number of neurons in the ganglion cell layer of retinal whole-mounts stained with cresyl violet. In the memantine group 47% of the neurons survived ischemia, in the cerestat group 61%, and in the riluzole group 43%. In the control group the percentage was 28%. The differences from the control group were statistically significant (P < 0.05). Cerestat, memantine and riluzole have a neuroprotective effect--reducing excitotoxic damage of retinal neurons. The relative drug potencies cannot be directly compared, because of differences in dosage and the route of administration.

ATP-sensitive K+Channels Mediate the Delayed Cardioprotective Effect of Adenosine A1Receptor Activation

Adenosine A1receptor stimulation increases myocardial resilence to ischaemia many hours later but the mechanism of protection is unclear. We hypothesized that A1receptor-induced delayed cardioprotection is mediated by KATPchannel opening. Rabbits were pretreated with saline or the selective A1receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), 0.1 mg/kg i.v. After 24 h, they were anaesthetized and subjected to 30 min left coronary artery occlusion (CAO) and 120 min reperfusion. Twenty minutes before CAO, either glibenclamide 0.3 mg/kg, sodium 5-hydroxydecanoate (5-HD) 5 mg/kg, or a corresponding volume of vehicle solution were given i.v. Infarct size as a percentage of ischaemic risk volume (I/R%) was assessed by triphenyltetrazolium. In the absence of either glibenclamide or 5-HD, CCPA pretreatment resulted in significant limitation of infarction (I/R 23.4±3.3%vs39.6±2.6% in saline pretreated animals,P<0.01). Administration of glibenclamide before CAO abolished this delayed protective effect of CCPA (I/R 37.4±4.7%), as did 5-HD (I/R 48.8±3.7%). Neither glibenclamide nor 5-HD significantly modified I/R in saline pretreated animals. Risk volume was similar in all groups (0.8–1.1 cm3). Systemic haemodynamic variables were not markedly different between any of the groups immediately before or during the ischaemia-reperfusion protocol. Thus, delayed protection following transient A1receptor activation was abolished by pre-ischaemic treatment with either glibenclamide or 5-HD, providing pharmacological evidence that KATPchannel opening mediates A1agonist-induced delayed myocardial protection. The inhibitory effect of 5-HD suggests specific involvement of mitochondrial KATPbut the mechanisms of sub-acute regulation of KATPfunction following A1receptor stimulation remain to be determined.

Neuroprotective role of ornithine decarboxylase activation in transient focal cerebral ischaemia: a study using ornithine decarboxylase-overexpressing transgenic rats.

Nuclear magnetic resonance imaging (MRI) was used to study dynamics of maturation and the size of ischaemic stroke lesions in rats with greatly increased activity of ornithine decarboxylase (ODC). Syngenic rats, either with or without chronic pre-ischaemic treatment with an ODC inhibitor, alpha-difluoromethylornithine (DFMO), as well as ODC-overexpressing transgenic rats were subjected either to transient middle cerebral artery (MCA) occlusion or permanent occlusion of the cortical branch of MCA. The two models were chosen to assess the role of ODC activity in damage caused by ischaemia and reperfusion, respectively. Diffusion of water was quantified by means of the trace of the diffusion tensor (D(av) = 1/3 Trace D) to assess the extent of energy failure and cytotoxic oedema, whereas the spin-spin relaxation time (T2) was used as a quantitative indicator of irreversible damage by MRI. Exposure to transient MCA occlusion resulted in significantly smaller stroke lesions in the ODC-overexpressing transgenic (246+/-14 mm3) than in syngenic (320+/-9 mm3) or DFMO-treated (442+/-63 mm3) rats as determined 48 h after the occlusion. The differences in sizes were due to smaller lesions in the cortical tissue (transgenic vs. syngenic) or both in cortical and striatal regions (transgenic vs. DFMO-treated animals). The degree of irreversible oedema was greater in DFMO-treated rats than in syngenic or transgenic animals indicating accelerated development of a permanent damage in the absence of ODC induction. Cortical infarct following permanent MCA occlusion developed faster in the DFMO-treated than in syngenic or transgenic rats as the lesion sizes at 10 h were 26.2+/-4.3 mm3, 14.2+/-2.3 mm3 and 12.3+/-1.9 mm3, respectively. However, the stroke volumes by 48 h were not statistically different in the three animal groups. The present data demonstrate that ODC activation is an endogenous neuroprotective measure in transient cerebral ischaemia.

N-methyl-1-deoxynojirimycin (MOR-14), an alpha-glucosidase inhibitor, markedly reduced infarct size in rabbit hearts.

N-methyl-1-deoxynojirimycin (MOR-14), an alpha-glucosidase inhibitor, reduces the glycogenolytic rate by inhibiting the alpha-1,6-glucosidase of glycogen-debranching enzyme in the liver, in addition to possessing an antihyperglycemic action by blocking alpha-1,4-glucosidase in the intestine. Because the reduction of the glycogenolytic rate may be one of the mechanisms of myocardial protection in ischemic preconditioning, the compounds inhibiting myocardial alpha-1,6-glucosidase may be protective against ischemic damage. Thus, we investigated whether MOR-14 could inhibit alpha-1,6-glucosidase and reduce the infarct size in rabbit hearts without collateral circulation. MOR-14 dose-dependently decreased the alpha-1,6-glucosidase activity in rabbit heart extract. A tracer study demonstrated the myocardial uptake of a considerable amount of MOR-14 sufficient to fully inhibit alpha-1,6-glucosidase. To assess the infarct size-reducing effect of MOR-14, 54 rabbits were subjected to 30-minute coronary occlusion followed by 48-hour reperfusion. Preischemic treatment with 25, 50, and 100 mg/kg of MOR-14 dose-dependently reduced the infarct size (to 26+/-4%, 19+/-3%, and 14+/-2% of the area at risk, respectively), compared with the saline control (45+/-5%) without altering the blood pressure or heart rate. Another 40 rabbits given 100 mg of MOR-14 or saline 10 minutes before ischemia were euthanized at 10 or 30 minutes of ischemia for biochemical analysis. MOR-14 decreased the alpha-1,6-glucosidase activity to approximately 20% in vivo, reduced the glycogen breakdown, and attenuated the lactate accumulation at both 10 and 30 minutes of ischemia. Preischemic treatment with MOR-14 preserved glycogen, attenuated the accumulation of lactate, and reduced the myocardial infarct size by 69%. This cardioprotective effect was independent of changes of blood pressure and heart rate or regional blood flow. It may be associated with alpha-1,6-glucosidase inhibition, because MOR-14 markedly decreased the alpha-1,6-glucosidase activity in the heart.

Ischemic Pretreatment Increases Cytoskeletal Association of 25 kD and 70 kD Heat-Shock Proteins and of Na,K-ATPase in Rat Renal Cortex after Repeat Ischemia † 1786

Ischemia results in increased induction of 25 kD and 70 kD HSPs in renal cortex. Recent research suggests interactions of these HSPs with cytoskeletal elements during the restoration of cellular polarity. To determine whether pretreatment with ischemia protects the membrane-cytoskeletal complex after repeat renal ischemia, we investigated cellular distribution of 25 kD and 70 kD HSPs and of Na,K-ATPase after a single and after repeat ischemia (45 min) in rat renal cortex.

Effects of KB-R7943, a novel Na+/Ca2+ exchange inhibitor, on myocardial ischemia/reperfusion injury

The effects of KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate) on major ion transporters were studied in canine cardiac sarcolemmal and sarcoplasmic reticular vesicles. KB-R7943 inhibited the Na+/Ca2+ exchange more potently than the Na+/H+ exchange, the Na+/K(+)-ATPase and the Ca2(+)-ATPase. The effects of KB-R7943 on ischemia/reperfusion-induced injury were studied in isolated rat perfused hearts in comparison with those of diltiazem and lidocaine. In normal hearts, diltiazem (10 microM) and lidocaine (100 microM) markedly reduced contractile function, but KB-R7943 (1, 10 microM) had no such effect. In the hearts subjected to 25-min ischemia and 30-min reperfusion, KB-R7943 concentration-dependently and significantly improved post-ischemic recovery of left ventricular developed pressure, left ventricular dP/dtmax and left ventricular end-diastolic pressure by pre-ischemic treatment (5 min) or post-ischemic treatment (10 min). Diltiazem and lidocaine showed similar improvement of recovery by pre-ischemic treatment, but they had no effect by post-ischemic treatment. Furthermore, the effect of KB-R7943 on arrhythmia was studied in anesthetized rats subjected to 5-min cardiac ischmeia and 10-min reperfusion. KB-R7943 (1, 10 mg/kg, i.v.) dose-dependently reduced the incidence and the duration of ventricular fibrillation. These results indicate that KB-R7943, a selective Na+/Ca2+ exchange inhibitor, has beneficial effects against myocardial ischemia/reperfusion injury and suggest that activation of the Na+/Ca2+ exchange mainly occurs immediately after reperfusion in the pathophysiological process of myocardial ischemia/reperfusion injury.

Effect of preischemic catecholamine treatment on ischemia-reperfusion injury of the myocardium: subtype, dose, and temperature dependency.

Preischemic adrenergic stimulation may affect postischemic cardiac function. Using an isolated working heart model, we investigated the effects of preischemic catecholamine treatment on postischemic recovery. Hearts from Wistar rats were perfused in working mode for 20 min, in Langendorff mode for 15 min, and again in working mode for 20 min (W2). Hearts were treated with isoproterenol (8.0 and 40.0 nmol/L), phenylephrine (0.06, 0.30, and 1.50 micromol/L), or epinephrine (16 and 80 nmol/L) during the W2 period and then arrested with St Thomas' Hospital cardioplegic solution (STH) and subjected to global ischemia (37 degrees C or 20 degrees C), followed by reperfusion. At 37 degrees C, isoproterenol had a beneficial effect at the lower dose but a harmful effect at the higher dose; phenylephrine and epinephrine had a harmful effect at all doses. At 20 degrees C, isoproterenol and epinephrine had a harmful effect at a high dose; phenylephrine had no harmful effect at any dose. In a separate study, the influence of calcium modulators (diltiazem and ryanodine, added in the STH) on the catecholamine effect was investigated. The harmful effect of preischemic treatment with isoproterenol (24.0 nmol/L) or phenylephrine (0.9 micromol/L) was abolished by the calcium modulators. Thus, preischemic beta-adrenergic or alpha + beta-adrenergic stimulation has a deleterious effect on postischemic recovery of the myocardium. The effect could be altered depending on the subtype and dose of catecholamine and the ischemic temperature. Intracellular calcium movement could be involved in the mechanism responsible for the harmful effect of preischemic catecholamine treatment.

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

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