The effect of coenzyme Q10 and cold cristalloid cardioplegia on hypothermic global ischemia

Coenzyme Q10 (CoQ10, ubiquinone) has been shown to be protective against myocardial ischemia/reperfusion induced injury. The purpose of this study was to investigate the effect of CoQ10 added to cold cristalloid cardioplegia on hypothermic ischemia and normothermic reperfusion using an isolated working rat heart. Hearts (n = 6-9/group) from male Wistar rats were aerobically (37 degrees C) perfused (20 min) with bicarbonate buffer. This was followed by a 3-min infusion of St. Thomas' Hospital cardioplegic solution containing various concentrations of CoQ10 (0, 1, 3, 6, 12, and 58 mumol/L). Hearts were then subjected to 180 min of hypothermic (20 degrees C) global ischemia and 35 min of normothermic (37 degrees C) reperfusion (15 min Langendorff, 20 min working). Ventricular fibrillation (Vf) upon reperfusion was irreversible in the 12 and 58 mumol/ L CoQ10 groups (4/6 and 3/6, respectively). In the hearts which Vf upon reperfusion was not irreversible, the percent recovery of aortic flow (%AF) was 43.3 +/- 5.4% (n = 9) in the control group versus 31.6 +/- 7.7% (n = 6), 38.0 +/- 12.0% (n = 6), 27.2 +/- 6.9% (n = 6), 31.3% (n = 2), and 30.4 +/- 14.2% (n = 3) in the 1, 3, 6, 12, and 58 mumol/L CoQ10 groups, respectively. Creatine kinase leakage during Langendorff reperfusion tended to be greater in the 12 and 58 mumol/L CoQ10 groups than in the control group. Thus, CoQ10 in the cold cristalloid cardioplegic solution induced irreversible Vf upon reperfusion and failed to improve functional recoveries following hypothermic global ischemia.     

Effect of postischemic reperfusion on microcirculation and lipid metabolism of skeletal muscle

To study the effect of ischemia reperfusion injury on microvascular reactivity and tissue metabolism in skeletal muscle, a Sprague-Dawley rat cremaster muscle was prepared as a tourniquet ischemia model and subjected to 2 hr ischemia followed by 1 hr reperfusion to simulate the timing of ischemia during microvascular surgery. The dose-response curve of arteriolar reactivity to norepinephrine, lipid peroxidation, and ultrastructure of capillaries was determined in both the control and postischemic reperfusion stages. Judging from the results, we summarize our observations as follows: (1) Postischemic reperfusion significantly increased arteriolar reactivity to norepinephrine, in which the EC50 for vasoconstriction decreased in all three orders of arterioles. These results suggest that reperfusion could have impaired the vasodilation control mechanism, possibly being endothelium dependent. (2) Lipid peroxidation increased sixfold in the reperfusion group, suggesting that oxygen free radicals have produced significant tissue damage under the created conditions. (3) Significant endothelial damage in the capillaries shown by electron microscope observation supports these studies, indicating that ischemia/reperfusion in clinically transplanted skeletal muscles could cause significant damage to the tissue microcirculation both physiologically and metabolically.     

Ischaemic myelopathy following aortic surgery or traumatic laceration of the aorta

Microcirculatory derangement, energy depletion and lipid peroxidation have been related to development of ischemia-reperfusion injury in the liver. This study investigates the effects of hyperbaric oxygen (HBO) on hepatic ischemia-reperfusion injury. Adult, male Sprague-Dawley rats were used. Three groups were evaluated: 1) sham-operated control (laparotomy only, no ischemia, no HBO), n=8; 2) ischemia control (1-h ischemia, 2-h reperfusion, no HBO), n=8; and 3) HBO pretreatment (100%, oxygen, 2.5 atm absolute, 90 min) plus ischemia (1-h ischemia, 2-h reperfusion), n=8. An in vivo microscope was used to investigate hepatic microcirculation. Tissue malondialdehyde (MDA) and adenosine triphosphate (ATP) were determined. In comparison with the ischemia control group, HBO significantly improved harmful insults following ischemia-reperfusion. HBO lessened adherent leukocyte count (6.00+/-1.31 cells/200 microm vs 11.38+/-2.88 cells/200 microm), and improved flow velocity (1.72+/-0.26 mm/s vs 0.83+/-0.19 mm/s) in post-sinusoidal venules. HBO also reduced MDA (1.04+/-0.24 nmol/mg protein vs 2.24+/-0.49 micromol/g protein), and increased ATP (2.03+/-0.17 micromol/g wet wt vs 0.73+/-0.11 micromol/g wet wt) levels. This study demonstrates that HBO before ischemia may ameliorate the ischemia-reperfusion injury of the liver in the rat model.     

Impact of N-acetylcysteine on the hepatic microcirculation after orthotopic liver transplantation

Recent observations showed an improvement of hepatic macro- and microhemodynamics as well as survival rates after warm ischemia of the liver following treatment with N-acetylcysteine (NAC). In this study we assessed the influence of NAC on the hepatic microcirculation after orthotopic liver transplantation (OLT) using intravital fluorescence microscopy. OLT with simultaneous arterialization was performed in 16 male Lewis rats following cold storage in University of Wisconsin solution for 24 hr. Within the experimental group (n = 8) donors received NAC (400 mg/kg) 25 min before hepatectomy. In addition, high-dose treatment of recipients with NAC (400 mg/kg) was started with reperfusion. Control animals (n = 8) received an equivalent amount of Ringer's solution. Intravital fluorescence microscopy was performed 30-90 min after reperfusion assessing acinar and sinusoidal perfusion, leukocyte-endothelium interaction, and phagocytic activity. Treatment with NAC reduced the number of nonperfused sinusoid from 52.4 +/- 0.8% to 15.7 +/- 0.5% (p = 0.0001) (mean +/- SEM). Furthermore, we achieved a significant reduction of leukocytes adhering to sinusoidal endothelium (per mm2 liver surface) from 351.9 +/- 13.0 in controls to 83.6 +/- 4.2 in the experimental group (P = 0.0001). In postsinusoidal venules, treatment with NAC decreased the number of sticking leukocytes (per mm2 endothelium) from 1098.5 +/- 59.6 to 425.9 +/- 37.7 (P = 0.0001). Moreover, bile flow was significantly increased after therapy with NAC (4.3 +/- 1.2 vs. 2.2 +/- 0.7 ml/90 min x 100g liver) (P < 0.05). Phagocytic activity was not influenced by application of NAC. We conclude that high-dose therapy with NAC in OLT attenuates manifestations of microvascular perfusion failure early after reperfusion and should be considered as a means to reduce reperfusion injury.     

Ischemic preconditioning in surgery of extremities: experimental studies

Ischemic preconditioning (IP), using one or more brief periods of ischemia, each followed by a short reperfusion phase, improves tolerance of subsequent sustained ischemia in different organs. The aim of this experimental study was to evaluate the effects of IP on postischemic function in skeletal muscle. Right hindlimbs of anesthetized rats were pretreated with three cycles each of 10 min of ischemia and 10 min of reperfusion (n = 12). Non-preconditioned animals (n = 12) served as controls. These hindlimbs were then subjected to 3 h of ischemia and 2 h of reperfusion. IP resulted in a significant increase in postischemic skeletal muscle force (240 +/- 47 mN vs 409 +/- 63 mN), force-time integral (1081 +/- 242 mN*s vs 2546 +/- 481 mN*s) and endurance (29.6 +/- 3.4 s vs 48.0 +/- 5.0 s). These data support the potential of IP to reduce postischemic skeletal muscle damage in surgery of the extremities using tourniquet ischemia. The concept deserves clinical evaluation.     

The effects of thyroid hormone modulation on rat liver injury associated with ischemia-reperfusion and cold storage

We investigated the effects of thyroid hormone modulation on liver injury associated with ischemia-reperfusion (I-R) and cold storage in rats. First, euthyroid and thyroxine (T4)-pretreated rats were exposed in vivo to 20-min global liver ischemia, then 30-min reperfusion. Liver injury was assessed by measuring serum alanine aminotransferase (ALT) levels. Liver concentrations of adenine nucleotides, reduced glutathione (GSH), and oxidized glutathione were evaluated. Second, rats were given the antithyroid drug propylthiouracil (PTU). Livers stored at 0-1 degrees C in Euro-Collins' solution for 20 h were reperfused at 37 degrees C for 15 min. Lactate dehydrogenase (LDH) in the effluent perfusate and bile flow were evaluated during reperfusion. Serum ALT levels increased after ischemia and I-R. ALT increased significantly more in T4-pretreated than in euthyroid rats after ischemia and I-R. Preischemic levels of adenosine triphosphate (ATP) were significantly lower in livers from T4-pretreated than in euthyroid rats (6.22 +/- 0.7 and 11 +/- 0.9 nmol/mg protein, respectively; P < 0.05). After ischemia, liver ATP was similarly reduced in T4-pretreated and euthyroid rats. After reperfusion, ATP partially recovered in euthyroid rats but remained low in T4-pretreated rats (6.7 +/- 1.0 and 1.91 +/- 0.7 nmol/mg protein, respectively; P < 0.05). Preischemic levels of liver GSH decreased to 44% in T4-pretreated rats. After ischemia, GSH decreased similarly in euthyroid and T4-pretreated rats. GSH recovered promptly after reperfusion in euthyroid rats but remained low in T4-pretreated rats (13.9 +/- 3.3 and 3.9 +/- 0.9 nmol/mg protein, respectively; P < 0.02). During reperfusion after cold storage, LDH in effluent perfusate was significantly lower and bile flow higher in livers from PTU-pretreated rats than from euthyroid rats. The histopathological changes observed after I-R and cold storage confirmed the biochemical findings. Our results suggest that T4 administration exacerbates pretransplant liver damage by increasing liver susceptibility to I-R, whereas PTU administration reduces the liver injury associated with cold storage. Implications: We studied the effects of thyroid hormone modulation on liver injury associated with ischemia-reperfusion and cold storage in rats. Thyroxine administration increased susceptibility to ischemia-reperfusion injury, whereas the antithyroid agent propylthiouracil reduced the deleterious effects associated with cold storage.     

Changes in vessel ultrastructure during ischemia and reperfusion of rabbit hindlimb: implications for therapeutic intervention

Peripheral ischemia was induced in the rabbit by occlusion of the left iliac artery for 6 hr, followed by 24 hr of reperfusion. Biochemical and morphological investigations were performed to evaluate the extent of vascular and tissue injury. Blood samples for plasma enzyme determinations (creatine kinase (CK) and lactate dehydrogenase (LDH) activities) were obtained at times t = 0, t = 6, t = 30 hr. Plasma CK and LDH activities in ischemic animals were approximately twice as high as those in sham-operated animals at the end of reperfusion, although no difference was observed at the end of the period of ischemia. Morphological and morphometric analysis of extensor digitorum longus muscle from ischemic animals showed a reduction in the number of patent capillary vessels per muscle fiber (1.54 +/- 0.1 and 1.04 +/- 0.09, P < 0.05, in sham and ischemic groups, respectively; mean +/- SEM). In addition, the number of microvilli on endothelial surfaces were considerably increased in the ischemic group (0.14 +/- 0.02 and 0.41 +/- 0.01 microns -2, P < 0.001, in sham and ischemic groups, respectively). A great number of adhered leucocytes were found on the vessel surface with some leucocytes having migrated through the vessel wall. Microcirculatory damage was accompanied by the formation of microthrombi which sometimes occluded the entire vessel lumen. The infusion of 1 mg/kg/hr of cloricromene for 6 hr prevented ischemic injury in microvessels and also prevented swelling of muscle mitochondria. In the treated group the number of patent capillaries per muscle fiber was very similar to that found in sham-operated animals (1.49 +/- 0.08; P < 0.01 vs. ischemic control). In conclusion, several different cell types are involved in the pathophysiological changes which occur in microvessels during ischemia/reperfusion injury. Pharmacological interventions, which inhibit the interactions of blood cells with endothelium, may be of value in the treatment of peripheral ischemia/reperfusion injury.     

Brief periods of occlusion and reperfusion increase skeletal muscle force output in humans

Prolonged periods of ischemia/reperfusion are known to deleteriously affect skeletal muscle performance. However, in animal models, brief bouts of both skeletal and cardiac muscle ischemia/reperfusion have been shown to decrease skeletal muscle injury and increase skeletal muscle force output, a phenomenon termed "preconditioning". Because there are transient periods of ischemia/reperfusion during isometric and concentric muscle contractions, the purpose of this study was to examine how short duration forearm occlusion/reperfusion prior to exercise, influenced isometric skeletal muscle force output in humans. Eleven subjects (6 men and 5 women, mean age 25 +/- 1 years) participated in this study. Using a Biodex multijoint ergometer, a protocol of isolated, isometric forearm wrist flexions was utilized to measure muscle force output in two separate trials. In the first trial, 15 isometric maximal voluntary contractions (MVCs) of the wrist flexors were performed in 20 intervals interspersed with 10 s of rest. In the second trial, forearm occlusion was induced (2 min at 200 mmHg by blood pressure cuff occlusion, with 10 s of hyperemia) prior to exercise. Following cuff occlusion, an identical exercise protocol was followed, i.e. 15 isometric wrist flexor MVCs performed in 20 intervals interspersed with 10 s of rest. The total force output over 15 MVCs was greater following intermittent cuff occlusion (no occlusion 2619 +/- 320 ft.lbs vs cuff occlusion 2986 +/- 195 ft.lbs; p < 0.05). The mean force output per MVC also increased during exercise following intermittent cuff occlusion (no occlusion 174 +/- 21 ft.lbs vs cuff occlusion 199 +/- 13 ft.lbs; p < 0.05). In a second set of experiments, we found a 3 to 4 fold hyperemic blood flow following cuff occlusion. These data suggest that brief periods of cuff occlusion/reperfusion may increase repetitive MVC force output by skeletal muscle. Although further study is needed to fully understand the effects of occlusion/reperfusion on skeletal muscle force output, we hypothesize that, in part, this putative effects is secondary to the hyperemic blood flow which follows cuff occlusion.     

Interactions between hypothermia and the latency to ischemic depolarization: implications for neuroprotection

BACKGROUND: The authors postulated that hypothermic neuroprotection can be attributed to a delayed onset of ischemic depolarization. METHODS: Halothane-anesthetized rats were prepared for near-complete forebrain ischemia. Direct current (DC) potential microelectrodes were placed in hippocampal CA1. The pericranial temperature was maintained at 31 degrees C, 33 degrees C, 35 degrees C, or 37 degrees C (n = 6 per group). Bilateral carotid occlusion with systemic hypotension was initiated for 10 min. The time to onset of the DC shift was recorded. In a second experiment, rats were assigned to 37 degrees C or 31 degrees C for 10 min of ischemia, or to 31 degrees C for 14 min of ischemia (n = 8 per group). These durations of ischemia were defined to allow 9 min of ischemic depolarization in the 37 degrees C-10 min and 31 degrees C-14 min groups. Neurologic and histologic outcomes were examined 7 days later. RESULTS: Hippocampal CA1 time to depolarization increased with decreasing temperature (P < 0.0001). Time to depolarization was increased by approximately 4 min in the rats maintained at 31 degrees C compared with those at 37 degrees C. Time to repolarization during reperfusion was not affected by temperature. Increasing the duration of ischemia from 10 min to 14 min with the pericranial temperature maintained at 31 degrees C resulted in a duration of depolarization that was equivalent in the 37 degrees C-10 min and 31 degrees C-14 min groups. However, hippocampal CA1 damage was not increased (31 degrees C-10 min = 4 +/- 1% dead neurons; 31 degrees C-14 min = 6 +/- 1% dead neurons, 95% CI, -1% to 3%; 37 degrees C-10 min = 90 +/- 17% dead neurons). CONCLUSIONS: Despite similar durations of DC depolarization, outcome in hypothermic rats was markedly improved compared with normothermic rats. This indicates that hypothermic neuroprotection can be attributed to mechanisms other than the delay in time to onset of ischemic depolarization.     

Staged reperfusion preserves the coronary flow reserve, especially in the regions not severely damaged by ischemic injury in the canine heart

The objective of this study was to determine the effects of staged reperfusion on the progressive reduction in coronary blood flow (CBF) and coronary flow reserve during reperfusion and on the infarct size in the canine heart. Fifteen dogs underwent 90 min of left circumflex coronary artery occlusion and 3 hr of reperfusion. In the abrupt reperfusion group, the occluder was released completely at the initiation of reperfusion. In the staged reperfusion group, CBF was maintained at 20% of preocclusion values for 10 min after initiation of reperfusion, then gradually released, and completely released 20 min after initiation of reperfusion. There was no significant difference in CBF between the staged (n = seven) and abrupt (n = eight) groups after 3 hr of reperfusion. The repayment of flow debt in the staged reperfusion group was significantly greater than in the abrupt reperfusion group after 3 hr of reperfusion (260+/-120% vs 100+/-60%, staged vs abrupt at 3 hr, p < 0.03). The ratio of peak reactive hyperemic flow to resting flow in the staged reperfusion group was significantly greater than in the abrupt reperfusion group throughout the reperfusion phase (4.4+/-1.0 vs 2.6+/-0.6 at 3 hr, p < 0.001), and had returned to the preocclusion values after 3 hr of reperfusion. This preservation of the coronary flow reserve in the staged reperfusion group was observed in the epicardium (4.1+/-0.6 vs 2.8+/-0.7, staged vs abrupt at 3 hr, p < 0.01), but not in the endocardium or midmyocardium. Infarct size did not differ significantly between the two groups. Staged reperfusion in this study did not appear to attenuate the reduction of CBF, or to reduce infarct size, however preserved the coronary flow reserve, especially in the regions not severely damaged by ischemic injury.     

Effects of transient coronary occlusion on the capillary network in the left ventricle of rat

The objective was to examine the changes in the capillary network in the left ventricle of rats subjected to transient occlusion of the left coronary artery followed by reperfusion (I-R). Eighteen Wistar rats were divided into three groups and all rats were anaesthetized with ethyl ether and artificially ventilated. The I-R 1 rats were subjected to a 3 min occlusion followed by reperfusion; the I-R 3 rats had three 3 min occlusions separated by 3 min of reperfusion; the Sham-operated rats underwent surgery but the coronary artery was not occluded. The thorax was closed at the end of the procedures and the rats were sacrificed for isolation of the hearts 30 d after treatment. Frozen sections of the left ventricles were cut and differential staining was used to classify the capillary portions. Five additional rats treated as the I-R 1 group were sacrificed at 120 min after reperfusion. Their left ventricles were used for immunohistochemical investigation of the early expression of bFGF and VEGF. By comparison with the Sham-operated rats, both I-R groups showed increases in the capillary density of total and venular capillary portions, an increased capillary : myocyte (C : M) ratio and a decrease in the capillary domain area in the three capillary portions. The changes in the I-R 1 group were significantly greater than those in the I-R 3 group, suggesting that the frequent experience of ischemic attack reduces the capacity of angiogenesis. In the rats sacrificed 120 min after the start of reperfusion, bFGF and VEGF were expressed on capillaries and in some myocytes. Punctate bFGF or VEGF staining was observed even 30 d after the transient ischemia. One 3 min occlusion of the left coronary artery followed by reperfusion produced changes in capillarity that would increase the oxygen supply to ventricular tissues. These effects may be attributed to the bFGF and VEGF expressed around capillaries. Repeated occlusions interspersed with a short period of reperfusion reduced the advantageous effects on capillarity.     

Inhibition of granulocyte-derived proteases reduces the increase in plasma endothelin associated with myocardial ischemia in the pig

Plasma endothelin (ET) is increased in association with myocardial infarction. The aim of the present study was to get insight into the mechanisms behind this ischemia-induced increase in plasma ET. Since granulocytes increase ET production in vitro, we examined to what extent inhibition of granulocyte-derived proteases could reduce the increase in plasma ET observed in association with myocardial ischemia. We infused Eglin C, a selective inhibitor of the granulocyte-derived proteases elastase, cathepsin G, and chymotrypsin, in pigs subjected to 90 min left anterior descending coronary artery occlusion followed by 210 min reperfusion (n = 7). Arterial plasma ET increased in an untreated control group (n = 7) from 5.0 +/- 0.6 (mean +/- SEM) fmol . ml-1 before myocardial ischemia to 6.1 +/- 0.6 fmol . ml. at 90 min ischemia and reached a maximum of 6.8 +/- 0.9 fmol . ml-1 at 90 min reperfusion. The increase in plasma ET associated with myocardial ischemia was almost completely abolished in the Eglin C treated group (p = 0.005). Plasma ET in the Eglin C treated animals was 4.7 +/- 0.4, 4.7 +/- 0.4, and 4.6 +/- 0.4 fmol . ml-1 before myocardial ischemia, at 90 min ischemia, and at 90 min reperfusion, respectively. Our study suggests a role for granulocyte-derived proteases in the increase in plasma ET associated with myocardial ischemia. We have shown that the increase in plasma ET associated with myocardial ischemia was reduced by inhibition of granulocyte-derived proteases using the selective protease inhibitor Eglin C.     

Adenosine transport inhibition ameliorates postischemic hypoperfusion in pigs

Cerebral ischemia is often followed by a period of delayed hypoperfusion that may contribute to tissue injury. We tested the hypothesis that augmentation of interstitial adenosine can improve tissue perfusion under this condition 10 min global ischemia was produced in two groups of isoflurane-anesthetized newborn pigs by occlusion of subclavian and brachiocephalic arteries, and changes in local cortical blood flow and cortical interstitial purine metabolites were measured using the combined hydrogen clearance-microdialysis technique. In one group, the dialysis probe was perfused with artificial cerebrospinal fluid buffer containing nitrobenzyl-thioinosine (NBT1, 100 mumol/l), a competitive inhibitor of adenosine transport. In the untreated group (n = 9), baseline cortical blood flow (39 +/- 3 ml/min/100 g) was depressed by 51 +/- 5% and 42 +/- 6% at 40 and 60 min, respectively, of postischemic reperfusion. NBTI increased baseline interstitial adenosine levels 2.4-fold which increased baseline cortical blood flow 1.5-fold to 60 +/- 4 ml/min/100 g, and increased both absolute adenosine levels as well as adenosine as a percentage of total purine metabolites throughout ischemia and reperfusion. As a result, the extent of postischemic hypoperfusion was significantly lessened in NBTI-treated animals (n = 9), with reductions in cortical blood flow of only 28 +/- 3% and 24 +/- 5% at 40 and 60 min of reperfusion, respectively. These results indicate that inhibition of adenosine transport by NBTI elevates interstitial adenosine concentration during and following cerebral ischemia, and concomitantly improves cortical perfusion in the post-ischemic period. The latter effect may contribute to the documented neuroprotective efficacy of adenosinergic therapy in cerebral ischemia.     

Transgenic A1 adenosine receptor overexpression markedly improves myocardial energy state during ischemia-reperfusion

A1 adenosine (A1AR) activation may reduce ischemia-reperfusion injury. Metabolic and functional responses to 30 min global normothermic ischemia and 20 min reperfusion were compared in wild-type and transgenic mouse hearts with approximately 100-fold overexpression of coupled cardiac A1ARs. 31P-NMR spectroscopy revealed that ATP was better preserved in transgenic v wild-type hearts: 53 +/- 11% of preischemic ATP remained after ischemia in transgenic hearts v only 4 +/- 4% in wild-type hearts. However, recovery of ATP after reperfusion was similar in transgenic (46 +/- 5%) and wild-type hearts (37 +/- 12%). Reductions in phosphocreatine (PCr) and cytosolic pH during ischemia were similar in both groups. However, recovery of PCR on reperfusion was higher in transgenic (67 +/- 8%) v wild-type hearts (36 +/- 8%), and recovery of pH was greater in transgenic (pH = 7.11 +/- 0.05) v wild-type hearts (pH = 6.90 +/- 0.02). Bioenergetic state ([ATP]/[ADP].[Pi]) was higher in transgenic v wild-type hearts during ischemia-reperfusion. Time to ischemic contracture was prolonged in transgenic (13.6 +/- 0.8 min) v wild-type hearts (10.4 +/- 0.3 min). Degree of contracture was lower and recovery of function in reperfusion higher in transgenic v wild-type hearts. In conclusion, A1AR overexpression reduces ATP loss and improves bioenergetic state during severe ischemic insult and reperfusion. These changes may contribute to improved functional tolerance.     

Mirror, mirror on the wall, who''s the thinnest one of all? Effects of self-awareness on consumption of full-fat, reduced-fat, and no-fat products

The aim of this study was to determine whether adenosine receptor blockade before ischemia would enhance the degree of stunning and induce a sustained decrease in glucose uptake after reperfusion. METHODS: Stunning was induced in 14 anesthetized swine by partially occluding the left anterior descending artery (LAD) for 20 min (> 80% flow reduction). Seven animals were pretreated with the nonspecific adenosine receptor blocker 8-phenyltheophylline (8-PT; 5 mg/kg), which decreased reactive hyperemia by an average of 38%. Myocardial glucose uptake was assessed 1 hr following reperfusion with PET and the glucose analog 18F-fluorodeoxyglucose (FDG). RESULTS: Before ischemia, systolic shortening in the LAD region was 15% +/- 6% in the control group and 16% +/- 4% in the 8-PT group and in both groups was reduced to - 1% +/- 2% during ischemia. After reperfusion, systolic shortening was 7% +/- 3% in the control group and 2% +/- 3% in the 8-PT group (p < 0.05). Myocardial oxygen consumption before ischemia was 4.58 +/- 3.03 micromol/min/g in the control group and 4.44 +/- 1.83 micromol/min/g in the 8-PT group (ns) and neither were different after reperfusion. In the postischemic LAD region, myocardial glucose uptake was 0.18 +/- 0.15 micromol/min/g in the control group and was similar to that of the 8-PT group (0.17 +/- 0.08 micromol/min/g; ns). CONCLUSION: The nonspecific adenosine blocker 8-PT enhanced the degree of stunning when given before ischemia but did not induce a sustained effect on myocardial glucose uptake after reperfusion.     

Alterations in contractility and intracellular Ca2+ transients in isolated bundles of skeletal muscle fibers from rats with chronic heart failure

To determine if chronic heart failure (CHF) leads to functional or structural alterations of skeletal muscle, we compared intracellular Ca2+ signaling, contractility, and the rate of fatigue development, together with electron microscopy (EM), in skeletal muscle preparations from rats with myocardial infarction-induced CHF versus sham-operated control rats. Bundles of 100 to 200 cells were dissected from the extensor digitorum longus (EDL) muscle of control (n = 13) and CHF (n = 19) rats and were either loaded with aequorin or fixed for EM. Muscles from CHF rats exhibited depressed tension development compared with control muscles during twitches (1.4 +/- 0.2 versus 2.8 +/- 0.7 g/mm2, P < .05) and maximal tetani (5.3 +/- 1.4 versus 10.7 +/- 2.4 g/mm2, P < .05). Depressed tension in CHF was accompanied by reduced quantitative [Ca2+]i release during twitches (0.7 +/- 0.1 versus 0.4 +/- 0.1 microM, P < .05) and during maximal tetani (1.8 +/- 0.3 versus 0.9 +/- 0.2 microM, P < .05). Skeletal muscle from CHF rats also demonstrated prolonged intracellular Ca2+ transients during twitches and tetani and accelerated fatigue development. EM revealed a lack of cellular atrophy in the CHF rats. In conclusion, EDL skeletal muscle from rats with CHF had intrinsic abnormalities in excitation-contraction coupling unrelated to cellular atrophy. These findings indicate that CHF is a condition accompanied by EDL skeletal muscle dysfunction.     

Exercise training reduces myocardial lipid peroxidation following short-term ischemia-reperfusion

PURPOSE: The purpose of these experiments was to test the hypothesis that endurance exercise training will reduce myocardial lipid peroxidation following short-term ischemia and reperfusion (I-R). METHODS: Female Sprague-Dawley rats (4 months old) were randomly assigned to either a sedentary control group (N = 13) or to an exercise training group (N = 13). The exercise trained animals ran 4 d.wk-1 (90 min.d-1) at approximately 75% V02max. Following a 10-wk training program, animals were anesthetized, mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was achieved by a ligature around the left coronary artery; occlusion was maintained for 5 min followed by a 10-min period of reperfusion. RESULTS: Although training did not alter (P > 0.05) myocardial activities of antioxidant enzymes (superoxide dismutase and glutathione peroxidase), training was associated with significant increase (P > 0.05) in heat shock protein (HSP72) in the left ventricle. Compared with controls, trained animals exhibited significantly lower levels (P < 0.05) of myocardial lipid peroxidation following I-R. CONCLUSION: These data support the hypothesis that exercise training provides protection against myocardial lipid peroxidation induced by short-term I-R in vivo.     

Effect of 3,4-diaminopyridine on rat extensor digitorum longus muscle paralyzed by local injection of botulinum neurotoxin

The actions of the K+ channel blocker, 3,4-diaminopyridine (3,4-DAP), were studied in the rat extensor digitorum longus (EDL) muscle following local inhibition of neuromuscular transmission by botulinum neurotoxin (BoNT). Local paralysis of the EDL muscle was induced by s.c. injections of BoNT serotypes A, B, E or F over the anterior tibialis muscle. One to 14 days later, the rats were anesthetized with urethane, and isometric twitch tensions following stimulation of the peroneal nerve were measured in situ. Muscles were paralyzed within 24 hr of administration of 5 mouse LD50 units (U) of BoNT/A and remained inhibited for the entire 14-day period of observation. Similar levels of inhibition, but of shorter duration, were observed after local injection of 20 U of BoNT/E, 10(4) U of BoNT/B or 20 U of BoNT/F. 3,4-DAP (4 mg/kg, i.v.) potentiated twitch tensions markedly in BoNT/A intoxicated muscle. The increase in tension developed rapidly (halftime = 5.81 +/- 0.6 min), persisted for approximately 1 hr, then decayed slowly with a halftime of 25.2 +/- 4.6 min. Subsequent administration of 3,4-DAP restored tensions to the original maxima, and this procedure could be repeated up to eight times with no decrement. The action of 3,4-DAP was comparable when given 1, 2, 3 or 7 days after BoNT/A and enhanced when administered 14 days after toxin injection. 3,4-DAP was less effective in reversing BoNT/E-induced muscle paralysis and nearly ineffective in antagonizing the paralytic actions of BoNT/B or BoNT/F. The results indicate that 3,4-DAP is of benefit in BoNT/A and BoNT/E intoxication, but is of marginal value after exposure to serotypes B and F.     

Autoregulation during pressor response elevates wall shear rate in arterioles

Autoregulation of blood flow implies reciprocal changes in vessel diameter and red blood cell velocity (VRBC) when perfusion pressure is altered. We tested two hypotheses: 1) blood flow will be autoregulated throughout arteriolar networks during a pressor response, and 2) wall shear rate (WSR; proportional to VRBC/diameter) will increase during autoregulation. Male hamsters (109 +/- 3 g; n = 22) were anesthetized (pentobarbital sodium 60 mg/kg), and the cremaster muscle was prepared for intravital videomicroscopy. Internal diameter and VRBC were monitored in first (1A)- through fourth (4A)-order arterioles; WSR and blood flow were calculated. Data were acquired at rest and at the peak of diameter responses to bilateral carotid artery occlusion (CAO). At rest, 1) mean arterial and 1A transmural pressures were 100 +/- 5 and 59 +/- 4 mmHg, respectively; 2) as branch order increased, arteriolar diameter, VRBC, and blood flow decreased (P < 0.05); and 3) WSR and resting tone increased with branch order (P < 0.05). During pressor responses to CAO, 1) arterial and 1A pressures increased to 145 +/- 7 and 89 +/- 5 mmHg, respectively (P < 0.05); 2) 1A branches dilated while 2A, 3A, and 4A branches constricted (P < 0.05); 3) VRBC and WSR increased in all branches (P<0.05); and 4) blood flow increased in 1A and 2A branches (P < 0.05), yet was unchanged (i.e., was autoregulated) in 3A and 4A branches. Arteriolar constrictions during CAO were not affected by alpha-adrenoceptor blockade with phentolamine (10(-6) M). We conclude that autoregulation of muscle blood flow during a pressor response involves myogenic constriction of arterioles with concomitant elevation of WSR.