Insulin and glycolysis dependency of cardioprotection by nicotinamide riboside.

Decreased nicotinamide adenine dinucleotide (NAD+) levels contribute to various pathologies such as ageing, diabetes, heart failure and ischemia-reperfusion injury (IRI). Nicotinamide riboside (NR) has emerged as a promising therapeutic NAD+ precursor due to efficient NAD+ elevation and was recently shown to be the only agent able to reduce cardiac IRI in models employing clinically relevant anesthesia. However, through which metabolic pathway(s) NR mediates IRI protection remains unknown. Furthermore, the influence of insulin, a known modulator of cardioprotective efficacy, on the protective effects of NR has not been investigated. Here, we used the isolated mouse heart allowing cardiac metabolic control to investigate: (1) whether NR can protect the isolated heart against IRI, (2) the metabolic pathways underlying NR-mediated protection, and (3) whether insulin abrogates NR protection. NR protection against cardiac IRI and effects on metabolic pathways employing metabolomics for determination of changes in metabolic intermediates, and 13C-glucose fluxomics for determination of metabolic pathway activities (glycolysis, pentose phosphate pathway (PPP) and mitochondrial/tricarboxylic acid cycle (TCA cycle) activities), were examined in isolated C57BL/6N mouse hearts perfused with either (a) glucose + fatty acids (FA) ("mild glycolysis group"), (b) lactate + pyruvate + FA ("no glycolysis group"), or (c) glucose + FA + insulin ("high glycolysis group"). NR increased cardiac NAD+ in all three metabolic groups. In glucose + FA perfused hearts, NR reduced IR injury, increased glycolytic intermediate phosphoenolpyruvate (PEP), TCA intermediate succinate and PPP intermediates ribose-5P (R5P) / sedoheptulose-7P (S7P), and was associated with activated glycolysis, without changes in TCA cycle or PPP activities. In the "no glycolysis" hearts, NR protection was lost, whereas NR still increased S7P. In the insulin hearts, glycolysis was largely accelerated, and NR protection abrogated. NR still increased PPP intermediates, with now high 13C-labeling of S7P, but NR was unable to increase metabolic pathway activities, including glycolysis. Protection by NR against IRI is only present in hearts with low glycolysis, and is associated with activation of glycolysis. When activation of glycolysis was prevented, through either examining "no glycolysis" hearts or "high glycolysis" hearts, NR protection was abolished. The data suggest that NR's acute cardioprotective effects are mediated through glycolysis activation and are lost in the presence of insulin because of already elevated glycolysis.

Effects of combined helium pre/post-conditioning on the brain and heart in a rat resuscitation model.

BACKGROUND: The noble gas helium induces cardio- and neuroprotection by pre- and post-conditioning. We investigated the effects of helium pre- and post-conditioning on the brain and heart in a rat resuscitation model. METHODS: After approval by the Animal Care Committee, 96 Wistar rats underwent cardiac arrest for 6 min induced by ventricular fibrillation. Animals received 70% helium and 30% oxygen for 5 min before cardiac arrest and for 30 min after restoration of spontaneous circulation (ROSC). Control animals received 70% nitrogen and 30% oxygen. Hearts and brains were excised after 2, 4 h or 7 days. Neurological degeneration was evaluated using TUNEL and Nissl staining in the hippocampal CA-1 sector. Cognitive function after 7 days was detected with the tape removal test. Molecular targets were measured by infrared western blot. Data are shown as median [Interquartile range]. RESULTS: Helium treatment resulted in significantly less apoptosis (TUNEL positive cells/100 pixel 73.5 [60.3-78.6] vs.78.2 [70.4-92.9] P = 0.023). Changes in Caveolin-3 expression in the membrane fraction and Hexokinase-II in the mitochondrial fraction were observed in the heart. Caveolin-1 expression of treated animals significantly differed from control animals in the membrane fraction of the heart and brain after ROSC. CONCLUSION: Treatment with helium reduced apoptosis in our resuscitation model. Differential expression levels of Caveolin-1, Caveolin-3 and Hexokinase II in the heart were found after helium pre- and post-conditioning. No beneficial effects were seen on neurofunctional outcome.

Modeling non-linear kinetics of hyperpolarized [1-(13)C] pyruvate in the crystalloid-perfused rat heart.

Hyperpolarized (13)C MR measurements have the potential to display non-linear kinetics. We have developed an approach to describe possible non-first-order kinetics of hyperpolarized [1-(13)C] pyruvate employing a system of differential equations that agrees with the principle of conservation of mass of the hyperpolarized signal. Simultaneous fitting to a second-order model for conversion of [1-(13)C] pyruvate to bicarbonate, lactate and alanine was well described in the isolated rat heart perfused with Krebs buffer containing glucose as sole energy substrate, or glucose supplemented with pyruvate. Second-order modeling yielded significantly improved fits of pyruvate-bicarbonate kinetics compared with the more traditionally used first-order model and suggested time-dependent decreases in pyruvate-bicarbonate flux. Second-order modeling gave time-dependent changes in forward and reverse reaction kinetics of pyruvate-lactate exchange and pyruvate-alanine exchange in both groups of hearts during the infusion of pyruvate; however, the fits were not significantly improved with respect to a traditional first-order model. The mechanism giving rise to second-order pyruvate dehydrogenase (PDH) kinetics was explored experimentally using surface fluorescence measurements of nicotinamide adenine dinucleotide reduced form (NADH) performed under the same conditions, demonstrating a significant increase of NADH during pyruvate infusion. This suggests a simultaneous depletion of available mitochondrial NAD(+) (the cofactor for PDH), consistent with the non-linear nature of the kinetics. NADH levels returned to baseline following cessation of the pyruvate infusion, suggesting this to be a transient effect.

Mitochondrial hexokinase and cardioprotection of the intact heart.

The interaction of hexokinase with mitochondria has emerged as a powerful mechanism in protecting many cell types against cell death. However, the role of mitochondrial hexokinase (mitoHK) in cardiac ischemia-reperfusion injury has as of yet received little attention. In this review we examine whether increased binding of hexokinase to the mitochondrion is also an integral component of cardioprotective signalling. We discuss observations in cardiac mitochondrial activation that directed us to the hypothesis of hexokinase cellular redistribution with reversible, cardioprotective ischemia, summarize the data showing that many cardioprotective interventions, such as ischemic preconditioning, insulin, morphine and volatile anesthetics, increase mitochondrial hexokinase binding within the intact heart, and discuss similarities between mitochondrial hexokinase association and ischemic preconditioning. Although most data indicate that mitochondrial hexokinase may indeed be an integral part of cardioprotection, a definitive proof for a causal relation between the amount of mitoHK and cardiac ischemia-reperfusion injury in the intact heart is eagerly awaited. When such relationship is indeed observed, the association of hexokinase with mitochondria will offer an opportunity to develop new therapies to combat ischemic cardiac diseases.

Perioperative hyperinsulinaemic normoglycaemic clamp causes hypolipidaemia after coronary artery surgery.

BACKGROUND: Glucose-insulin-potassium (GIK) administration is advocated on the premise of preventing hyperglycaemia and hyperlipidaemia during reperfusion after cardiac interventions. Current research has focused on hyperglycaemia, largely ignoring lipids, or other substrates. The present study examines lipids and other substrates during and after on-pump coronary artery bypass grafting and how they are affected by a hyperinsulinaemic normoglycaemic clamp. METHODS: Forty-four patients were randomized to a control group (n=21) or to a GIK group (n=23) receiving a hyperinsulinaemic normoglycaemic clamp during 26 h. Plasma levels of free fatty acid (FFA), total and lipoprotein (VLDL, HDL, and LDL)-triglycerides (TG), ketone bodies, and lactate were determined. RESULTS: In the control group, mean FFA peaked at 0.76 (sem 0.05) mmol litre(-1) at early reperfusion and decreased to 0.3-0.5 mmol litre(-1) during the remaining part of the study. GIK decreased FFA levels to 0.38 (0.05) mmol litre(-1) at early reperfusion, and to low concentrations of 0.10 (0.01) mmol litre(-1) during the hyperinsulinaemic clamp. GIK reduced the area under the curve (AUC) for FFA by 75% and for TG by 53%. The reduction in total TG was reflected by a reduction in the VLDL (-54% AUC) and HDL (-42% AUC) fraction, but not in the LDL fraction. GIK prevented the increase in ketone bodies after reperfusion (-44 to -47% AUC), but was without effect on lactate levels. CONCLUSIONS: Mild hyperlipidaemia was only observed during early reperfusion (before heparin reversal) and the hyperinsulinaemic normoglycaemic clamp actually resulted in hypolipidaemia during the largest part of reperfusion after cardiac surgery.

Differential effects of a perioperative hyperinsulinemic normoglycemic clamp on the neurohumoral stress response during coronary artery surgery.

BACKGROUND: Hyperglycemia in patients undergoing coronary artery bypass grafting (CABG) is associated with adverse outcome. Although insulin infusion strategies are increasingly used to improve outcome, a pathophysiological rationale is currently lacking. The present study was designed to quantify the effects of a perioperative hyperinsulinemic normoglycemic clamp on the neurohumoral stress response during CABG. METHODS: Forty-four nondiabetic patients, scheduled for elective CABG, were randomized to either a control group (n = 22) receiving standard care or to a clamp group (n = 22) receiving additionally a perioperative hyperinsulinemic (regular insulin at a fixed rate of 0.1 IU.kg(-1).h(-1)) normoglycemic (plasma glucose between 3.0 and 6.0 mmol.liter(-1)) clamp during 26 h. We measured the endocrine response of the hypothalamus-pituitary-adrenal (HPA) axis, the sympathoadrenal axis, and glucagon, as well as plasma glucose and insulin at regular intervals from the induction of anesthesia at baseline through the end of the second postoperative day (POD). RESULTS: There were no differences in clinical outcome between the groups. In the control group, hyperglycemia developed at the end of surgery and remained present until the final measurement point on POD2, whereas plasma insulin levels remained unchanged until the morning of POD1. In the intervention group, normoglycemia was well maintained during the clamp, whereas insulin levels ranged between 600 and 800 pmol.liter(-1). In both groups, plasma ACTH and cortisol increased from 6 h after discontinuation of cardiopulmonary bypass onward. However, during the clamp period, a marked reduction in the HPA axis response was found in the intervention group, as reflected by a 47% smaller increase in area under the curve in plasma ACTH (P = 0.035) and a 27% smaller increase in plasma cortisol (P = 0.002) compared with the control group. Compared with baseline, epinephrine and norepinephrine increased by the end of the clamp interval until POD2 in both groups. Surprisingly, the area under the curve of epinephrine levels was 47% higher (P = 0.026) after the clamp interval in the intervention group as compared with the control group. CONCLUSION: A hyperinsulinemic normoglycemic clamp during CABG delays and attenuates the HPA axis response during the first 18 h of the myocardial reperfusion period, whereas after the clamp, plasma epinephrine is higher. The impact of delaying cortisol responses on clinical outcome of CABG remains to be elucidated.

Undiminished mitochondrial function during stunning in rabbit heart at 28 degrees C.

OBJECTIVE: To investigate effect of brief ischemia on mitochondrial function in intact myocardium, rather than in isolated mitochondria. METHODS: The mitochondrial response was characterized by the mean response time (tmito) of cardiac mitochondrial O2 consumption to steps in heart rate. Isolated isovolumic rabbit hearts were perfused at 28 degrees C with a constant flow of Tyrode solution containing 11 mM glucose. O2 consumption and tmito were determined before ischemia and after 25 min of no-flow global ischemia during which hearts were either paced (I + P, n = 8) or unpaced (I - P, n = 8). A non-ischemic control group (N = 8) was also examined. RESULTS: At 20 min reperfusion, developed left ventricular pressure (DLVP) after I + P was decreased to 47 +/- 3% (mean +/- s.e.m.; P < 0.05) of control DLVP without significant changes in venous creatine kinase efflux, indicating contractile stunning. In contrast complete contractile recovery was observed after I - P. Before ischemia, tmito was 11.2 +/- 0.6 and 14.9 +/- 0.7 s for heart rate steps from 60 to 70 and from 60 to 120 beats/min, respectively. The tmito was lower (P < 0.05) for the corresponding downward steps (10.5 +/- 0.6 and 12.4 +/- 0.6 s, respectively). An increase (P < 0.05) in tmito was observed in the course of the experiment for upward (1.2 +/- 0.3 s) and downward steps (1.4 +/- 0.3 s), but the change was similar after ischemia to that in time-matched controls (P > 0.05, both for I - P and I + P vs. control). Oxygen consumption, compared at fixed levels of the rate x pressure product, was unchanged after ischemia (P > 0.05, for both I - P and I + P vs. controls), suggesting undiminished efficiency of mitochondrial ATP production. CONCLUSIONS: Twenty-five minutes ischemia does not affect mitochondrial function in rabbit hearts at 28 degrees C, even when contractile stunning resulted.

Functional heterogeneity of oxygen supply-consumption ratio in the heart.

In this review, the regional heterogeneity of the oxygen supply-consumption ratio within the heart is discussed. This is an important functional parameter because it determines whether regions within the heart are normoxic or dysoxic. Although the heterogeneity of the supply side of oxygen has been primarily described by flow heterogeneity, the diffusional component of oxygen supply should not be ignored, especially at high resolution (tissue regions << 1 g). Such oxygen diffusion does not seem to take place from arterioles or venules within the heart, but seems to occur between capillaries, in contrast to data recently obtained from other tissues. Oxygen diffusion may even become the primary determinant of oxygen supply during obstructed flow conditions. Studies aimed at modelling regional blood flow and oxygen consumption have demonstrated marked regional heterogeneity of oxygen consumption matched by flow heterogeneity Direct, non-invasive indicators of the balance between oxygen supply and consumption include NADH videofluorimetry (mitochondrial energy state) and microvascular PO2 measurement by the Pd-porphyrin phosphorescence technique. These indicators have shown a relatively homogeneous distribution during physiological conditions supporting the notion of regional matching of oxygen supply with oxygen consumption. NADH videofluorimetry, however, has demonstrated large increases in functional heterogeneity of this ratio in compromised hearts (ischemia, hypoxia, hypertrophy and endotoxemia) with specific areas, referred to as microcirculatory weak units, predisposed to showing the first signs of dysoxia. It has been suggested that these weak units show the largest relative reduction in flow (independent of absolute flow levels) during compromising conditions, with dysoxia initially developing at the venous end of the capillary.

Inhibition of the pentose phosphate pathway decreases ischemia-reperfusion-induced creatine kinase release in the heart.

OBJECTIVE: The oxidative pentose phosphate pathway (oxPPP) produces NADPH, which can be used to maintain glutathione in its reduced state (anti-oxidant; beneficial effects) or to produce radicals or nitric oxide (NO) through NADPH oxidase/NO synthase (detrimental effects). Changes in cytosolic redox status have been implicated in ischemic preconditioning (PC). This study investigates whether (1) PC affects mitochondrial redox state, (2) the oxPPP plays a protective or detrimental role in ischemia (I)-reperfusion (R) injury in the intact heart and (3) PPP is altered with PC. METHODS: Isolated rat hearts were subjected to 40-min global I and 30-min R (CO, control). Ischemia was either preceded by three 5-min I/R periods (PC) and/or oxPPP inhibition by 6-aminonicotinamide (6AN) or NADPH oxidase/NO synthase inhibition by diphenyleneiodonium (DPI). NADH videofluorometry was used to determine mitochondrial redox state. PPP intermediates were determined in CO and PC hearts using tandem mass spectrometry. RESULTS: PC reduced ischemic damage (creatine kinase, CK, release from 337+/-64 to 147+/-41 U/R/gdw) and contracture (from 59+/-5 to 31+/-3 mm Hg) and increased recovery of contractility (from 48+/-10% to 88+/-8%), as compared to CO. PC was without effect on NADH fluorometry. Inhibition of the oxPPP reduced injury (CK release: 91+/-24 U/R/gdw) to similar levels as PC, without improving contractility. Inhibition of NADPH oxidase/NO synthase mimicked the effects of oxPPP inhibition on injury (CK release: 140+/-22 U/R/gdw). Although levels of ribose-5P and (ribulose-5P+xylulose-5P) rose several fold during ischemia with minor changes in sedoheptulose-7P, demonstrating an active PPP in the heart, PC did not affect these levels. CONCLUSIONS: (1) PC can attenuate cardiac reperfusion injury without alterations in mitochondrial redox state; (2) inhibition of the oxPPP protects the heart against I/R-induced CK release; and (3) PC does not result in altered activity of the PPP.

Increased hypoxic stress decreases AMP hydrolysis in rabbit heart.

OBJECTIVE: AMP conversion to adenosine by cytosolic 5'nucleotidase (5NT) or to IMP by AMP deaminase determines the degree of nucleotide degradation, and thus ATP resynthesis, during reoxygenation. To elucidate the regulation of AMP hydrolysis during ischemia, data from 31P NMR spectroscopy and biochemical analyses were integrated via a mathematical model. Since 5NT is downregulated during severe underperfusion (5% flow), we tested 5NT regulation during less severe underperfusion (10% flow) and then made the perfusate hypoxic to see if the greater stress reactivated 5NT. METHODS: 31P NMR spectra and coronary venous effluents were obtained from Langendorff-perfused rabbit hearts subjected to two 30-min periods of underperfusion (10% flow); the second period with or without additional hypoxia (30% O2). Data were analyzed with a mathematical model describing the kinetics of myocardial energetics and metabolism. RESULTS: A single 30-min period of 10% flow causes downregulation of AMP hydrolysis and the data from the second period of underperfusion are best described by lower 5NT activity, even in the presence of extra hypoxia. Thirty percent less purines appear in the venous effluent than predicted by the phosphoenergetics (PCr and ATP) when IMP is not allowed to accumulate by the model, however the model indicates that a constant accumulation of IMP via AMP deaminase could explain the discrepancy between expected and measured purines in the venous effluent. CONCLUSIONS: While AMP hydrolysis to adenosine is prominent in early ischemia and acts to preserve cellular energy potential, during a second ischemic period, nucleotides are conserved by the stable inhibition of AMP hydrolysis. Furthermore, during 10% flow conditions, nucleotides are conserved, possibly via an IMP-accumulatory pathway.

Changes in geometry of actively shortening unipennate rat gastrocnemius muscle.

Muscle geometry of the unipennate medial gastrocnemius (GM) muscle of the rat was examined with photographic techniques during isometric contractions at different muscle lengths. It was found that the length of fibers in different regions of GM differs significantly, and proximal aponeurosis length varies significantly from distal aponeurosis length; the angle of the aponeurosis with the muscular action differs significantly among regions at short muscle lengths (full contraction). These data support the idea that the unipennate GM cannot be represented by a parallelogram in a two-dimensional analysis. As the muscle shortens, the area of the mid-longitudinal plane of the GM decreases by 24%, a decrease that may be explained by assuming fiber diameter to increase in all directions. The angle between fiber and aponeurosis is determined by more than fiber length. Hence, such important assumptions as a parallelogram with constant area and fiber angle gamma changes determined by fiber length changes, frequently used in the theoretical analysis of the morphological mechanism of unipennate muscle contraction, do not hold for the unipennate GM of the rat. Length of the sarcomere within the mid-longitudinal plane of GM varies from 1.92 to 2.14 microns among the different muscle regions at muscle optimum length (length at which force production is highest), whereas shortening to 6 mm less than optimum length produces a range of sarcomere lengths from 0.89 to 1.52 microns. These data suggest that fibers located in different regions of the GM reach their optimum and slack lengths at various muscle lengths.

Influence of muscle geometry on shortening speed of fibre, aponeurosis and muscle.

The influence of muscle geometry on muscle shortening of the gastrocnemius medialis muscle (GM) of the rat was studied. Using cinematography, GM geometry was studied during isokinetic concentric activity at muscle lengths ranging from 85 to 105% of the optimum muscle length. The shortening speed of the distal fibre, the proximal aponeurosis and the muscle were determined, as well as the effect of rotation of the distal fibre and the proximal aponeurosis on the muscle speed of shortening. The results show that, due to the geometrical configuration, muscle shortening speed is not only determined by the speed of the fibre, but also to a large extent by the aponeurosis shortening speed. At optimum muscle length, the fibre and aponeurosis shortening speeds expressed relative to the muscle shortening speed amounted to 84% and 6%, respectively. At shorter muscle length, fibre speed relative to muscle speed decreased to values as low as 35%, whereas that of aponeurosis increased to values as high as 31%. Angular effects on the muscle speed of shortening can explain 10% of the muscle shortening speed at optimum muscle length and up to 34% of the muscle speed at shorter muscle length. In addition, a model was formulated to simulate the geometrical effects on muscle speed. This model, incorporating both fibre and aponeurosis length changes, contains a transfer function relating the shortening speeds of fibre and aponeurosis to muscle speed. The muscle shortening speed calculated using this transfer function demonstrated no significant differences with the speed measured experimentally.

Mean sarcomere length-force relationship of rat muscle fibre bundles.

To study how sarcomere length inhomogeneities and the duration of activation affect sarcomere length-force characteristics of muscle, the mean sarcomere length-force relationship was determined for twitches and at 100 and 300 ms during tetanic activation for rat extensor digitorum longus and gastrocnemius medialis muscle fibre bundles. Mean sarcomere length is the mean length of all sarcomeres within the fibre, calculated by dividing fibre length by the number of sarcomeres in series in the fibre. The twitch mean sarcomere length-force relationship is shifted to larger sarcomere lengths (optimum mean sarcomere length = 2.69 microns) compared to the relationships determined at 100 or 300 ms of tetanic activation (optimum mean sarcomere length = 2.38 microns), which were the same. It is shown that the normalized Gordon et al. rationale results in a large overestimate of force (at most 68% of force at a sarcomere length of 1.60 microns) for mean sarcomere lengths between 1.4 and 2.0 microns, and in an underestimate of force between 2.3 and 3.0 microns. It is concluded that modelling skeletal mammalian muscle length-force relationships can be improved by using mean sarcomere length-force relations of mammalian fibres instead of the normalized rationale of Gordon et al. derived from a selected homogeneous part of frog fibre.

Length-force characteristics of the aponeurosis in the passive and active muscle condition and in the isolated condition.

Length behaviour of the entire and designated parts of the proximal aponeurosis of the unipennate gastrocnemius medialis (GM) muscle of the rat was examined at muscle lengths ranging form muscle slack length to 4 mm above muscle optimum length in the passive and active (isometric contractions) muscle condition (n = 13). In addition, length-force characteristics of the aponeurosis in the isolated condition were determined (n = 6). Going from muscle slack length to 4 mm above muscle optimum length, the relative extension (relative to the length at muscle slack length) yielded the following results: 14.3% for the entire aponeurosis, 9.8% for the most proximal 25% of the aponeurosis, 3-5% for the middle 50% of the aponeurosis and 52.3% for the most distal 25% of the aponeurosis. Aponeurosis length as a function of aponeurosis force was significantly shorter in the active compared to the passive or isolated condition for force values within the range of force encountered in all three conditions (0.3-1.0 N); no significant difference was observed between the passive or isolated condition. It is concluded that the extension of the aponeurosis is heterogeneously distributed along its length. Differences in aponeurosis length-force curves between the conditions may be explained in terms of a heterogeneous force distribution within the muscle.

Papillary muscle and left ventricle show different contractile and metabolic responses during myocardial stunning.

We conclude that a global ischemic/hypoxic insult results in a heterogeneous response of mechanical and mitochondrial performance in isolated Langendorff-perfused hearts. The results warn against the use of models of stunning in which stunning is determined for only one part (e.g. left ventricle) and effects of stunning are analyzed in other parts (e.g. right ventricular muscle). The results further suggest that some parts of the myocardium under some mechanical loading conditions can withstand 15 min of interrupted oxygen supply without strong negative effects on contractile function and the response time of oxidative phosphorylation.

Mast cells trigger epithelial barrier dysfunction, bacterial translocation and postoperative ileus in a mouse model.

BACKGROUND: Abdominal surgery involving bowel manipulation commonly results in inflammation of the bowel wall, which leads to impaired intestinal motility and postoperative ileus (POI). Mast cells have shown to play a key role in the pathogenesis of POI in mouse models and human studies. We studied whether mast cells contribute to the pathogenesis of POI by eliciting intestinal barrier dysfunction. METHODS: C57BL/6 mice, and two mast cell-deficient mutant mice Kit(W/W-v) , and Kit(W-sh/W-sh) underwent laparotomy (L) or manipulation of the small bowel (IM). Postoperative inflammatory infiltrates and cytokine production were assessed. Epithelial barrier function was determined in Ussing chambers, by measuring transport of luminal particles to the vena mesenterica, and by assessing bacterial translocation. KEY RESULTS: In WT mice, IM resulted in pro-inflammatory cytokine and chemokine production, and neutrophil extravasation to the manipulated bowel wall. This response to IM was reduced in mast cell-deficient mice. IM caused epithelial barrier dysfunction in WT mice, but not in the two mast cell-deficient strains. IM resulted in a decrease in mean arterial pressure in both WT and mast cell-deficient mice, indicating that impaired barrier function was not explained by tissue hypoperfusion, but involved mast cell mediators. CONCLUSIONS & INFERENCES: Mast cell activation during abdominal surgery causes epithelial barrier dysfunction and inflammation of the muscularis externa of the bowel. The impairment of the epithelial barrier likely contributes to the pathogenesis of POI. Our data further underscore that mast cells are bona fide cellular targets to ameliorate POI.

Glucose-insulin therapy, plasma substrate levels and cardiac recovery after cardiac ischemic events.

INTRODUCTION: The potential usefulness of glucose-insulin therapy relies to a large extent on the premise that it prevents hyperglycemia and hyperlipidemia following cardiac ischemic events. METHODS: In this review we evaluate the literature concerning plasma glucose and free fatty acids levels during and following cardiac ischemic events. RESULTS: The data indicate that hyperlipidemia and hyperglycemia most likely occur during acute coronary ischemic syndromes in the conscious state (e.g. acute myocardial infarction) and less so during reperfusion following CABG reperfusion. This is in accordance with observations that glucose-insulin therapy during early reperfusion post CABG may actually cause hypolipidemia, because substantial hyperlipidemia does not appear to occur during that stage of cardiac surgery. DISCUSSION: Considering recent data indicating that hypolipidemia may be detrimental for cardiac function, we propose that free fatty acid levels during reperfusion post CABG with the adjunct glucose-insulin therapy need to be closely monitored. CONCLUSION: From a clinical point of view, a strategy directed at monitoring and thereafter maintaining plasma substrate levels in the normal range for both glucose (4-6 mM) and FFA (0.2-0.6 mM) as well as stimulation of glucose oxidation, promises to be the most optimal metabolic reperfusion treatment following cardiac ischemic episodes. Future (preclinical and subsequently clinical) investigations are required to investigate whether the combination of glucose-insulin therapy with concomitant lipid administration may be beneficial in the setting of reperfusion post CABG.

Glucose, insulin and potassium applied as perioperative hyperinsulinaemic normoglycaemic clamp: effects on inflammatory response during coronary artery surgery.

BACKGROUND: The clinical benefits of glucose-insulin-potassium (GIK) and tight glycaemic control in patients undergoing coronary artery bypass grafting (CABG) may be partly explained by an anti-inflammatory effect. We applied GIK as a hyperinsulinaemic normoglycaemic clamp for >25 h and quantified its effect on systemic inflammation in patients undergoing CABG. METHODS: Data obtained in 21 non-diabetic patients with normal left ventricular function scheduled for elective coronary artery surgery, who were randomly allocated to a control or GIK group, were analysed. In GIK patients, regular insulin was infused at a fixed rate of 0.1 IU kg(-1) h(-1). The infusion rate of glucose (30%) was adjusted to maintain blood glucose levels within a target range of 4.0-5.5 mmol litre(-1). Plasma concentrations of interleukins 6, 8 and 10, C-reactive protein (CRP) and serum amyloid A (SAA) were measured on the day of surgery and on the first and second postoperative days (POD1 and POD2). RESULTS: In the GIK group hypoglycaemia (glucose <2.2 mmol litre(-1)) did not occur, whereas hyperglycemia (glucose >6.1 mmol litre(-1)) developed in 15% of all measurements. In control patients, hyperglycaemia developed in >80% of all measurements in the presence of low endogenous insulin levels. CRP and SAA levels increased in both groups, with maximum levels measured on POD2. GIK treatment significantly reduced CRP and SAA levels. Interleukin levels increased significantly in both groups following cardiopulmonary bypass, but no differences were found between the groups. CONCLUSION: Hyperinsulinaemic normoglycaemic clamp is an effective method of maintaining tight glycaemic control in patients undergoing CABG and it attenuates the systemic inflammatory response in these patients. This effect may partly contribute to the reported beneficial effect of glycaemic control in patients undergoing CABG.

Post-ischaemic changes in the response time of oxygen consumption to demand in the isolated rat heart are mediated partly by calcium and glycolysis.

This study examined whether different durations of ischaemia (I) and reperfusion (R) altered the kinetics of O(2) consumption-to-demand matching and the contribution of changes in calcium and metabolic pathways to possible alterations. The response time of mitochondrial O(2) consumption (t(mito)) to a step in heart rate in isolated rat hearts was used as index for the response time of O(2) consumption-to-demand matching. At baseline, t(mito) was 8.9 +/- 0.4 s for all groups. At 5 min reperfusion, after both reversible (I=5 or I=15 min) or irreversible (I=25 min) ischaemia, matching was accelerated (t(mito) relative to baseline: 53 +/- 8%, 64 +/- 8%, 51+/- 6% and 100 +/- 5% for I=5, 15, 25 min and control). At late reperfusion (>30 min), reversible ischaemia resulted in a slowing of the matching, whereas after irreversible ischaemia t(mito) recovered to control values (156 +/- 16%, 153 +/- 13%, 92 +/- 7%, 114 +/- 6%, for I=5,15, 25 min and control, respectively). High perfusate Ca(2+) mimicked (t(mito): 44 +/- 11%), whereas blocking mitochondrial Ca(2+) uptake attenuated the acceleration observed at early reperfusion (t(mito): 7 +/- 5%). Replacing glucose with substrates used downstream of glycolysis (11 mM lactate or 11 mM pyruvate) abolished the reversible ischaemia-induced slowing of the matching at late reperfusion. It is concluded that I/R-induced changes in the kinetics of O(2) consumption-to demand matching depend critically on the duration of ischaemia and reperfusion. The data indicate that I/R-induced increases in Ca(2+) may, at least partly, explain the faster kinetics at early reperfusion, whereas I/R-induced increases in glycolysis from exogenous glucose result in slower matching of O(2) consumption-to-demand at late reperfusion.

Influence of muscle shortening on the geometry of gastrocnemius medialis muscle of the rat.

For static and dynamic conditions muscle geometry of the musculus gastrocnemius medialis of the rat was compared at different muscle lengths. The dynamic conditions differed with respect to isokinetic shortening velocity (25, 50 and 75 mm/s) of the muscle-tendon complex and in constancy of force (isotonic) and velocity (isokinetic) during shortening. Muscle geometry was characterized by fibre length and angle as well as aponeurosis length and angle. At high isokinetic shortening velocities (50 and 75 mm/s) small differences in geometry were found with respect to isometric conditions: aponeurosis lengths differed maximally by -2%, fibre length only showed a significant increase (+3.2%) at the highest shortening velocity. The isotonic condition only yielded significant differences of fibre angle (-4.5%) in comparison with isometric conditions. No significant differences of muscle geometry were found when comparing isotonic with isokinetic conditions of similar shortening velocity. The small differences of geometry between isometric and dynamic conditions are presumably due to the lower muscle force in the dynamic condition and the elastic behaviour of the aponeurosis. It is concluded that, unless very high velocities of shortening are used, the relationship between muscle geometry and muscle length in the isometric condition may be used to describe muscle geometry in the dynamic condition.