Myocardial Glycogen Research Articles

Amrinone improves postischemic myocardial metabolism in the rat heart-lung preparation.

Amrinone, a phosphodiesterase inhibitor, is a non-glycosidic noncatecholamine with both vasodilator and positive inotropic effects. We were interested in assessing the effect of amrinone on postischemic cardiac performance in the isolated heart-lung preparation. Twenty-four male Wistar-ST rats were used. They were randomly divided into three groups. Amrinone, 10 μg·ml-1 or 100 μg·ml-1 was administered 8 min after the start of perfusion except in the control group. Ten minutes after the start of perfusion, all hearts were made globally ischemic for 8 min. Subsequently, the preparations were reperfused for 10 min. At the end of the experimental period, the hearts were freeze-clamped, and then myocardial high-energy phosphates, lactate, pyruvate, and glycogen were measured. Hemodynamic parameters in all groups decreased significantly during ischemia. However, there were no significant differences among the groups. The myocardial ATP level in the 100 μg·ml-1 group was significantly higher than that in the control group. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP) levels in the 100 μg·ml-1 group were significantly lower than those in the control group. Myocardial lactate, pyruvate, and glycogen levels were not significantly different among the groups. This result suggests that amrinone improves postischemic myocardial metabolism. Although we could not measure coronary flow, amrinone might increase coronary flow with direct coronary vasodilation which would have increased the myocardial ATP and energy charge levels.

Magnesium depletion impairs myocardial carbohydrate and lipid metabolism and cardiac bioenergetics and raises myocardial calcium content in-vivo: relationship to etiology of cardiac diseases.

This study examines the effects of Mg depletion on myocardial bioenergetic, carbohydrate, lipid and phospholipid metabolism. Rats were studied after long-term (12 week) selective dietary restriction of Mg (20% normal dietary intake). Myocardial biopsy samples were examined for glucose 6-phosphate and glycogen to evaluate carbohydrate pathways and for glycerol phosphate and mitochondrial fatty acid oxidation and phospholipid contents to evaluate lipid and phospholipid turnover. Dietary Mg deficiency resulted in falls in myocardial glycogen, glucose-6-phosphate, glycerol phosphate, as well as the contents of phosphatidylcholine (PC), phosphatidylethanolamine (PE), diphosphatidyl glycerol (DPG), phosphatidyl inositol (PI) and total phospholipid phosphorus. These observations demonstrate impaired phospholipid metabolism, probably at the biosynthetic level. The mitochondrial oxidation of long-chain fatty acids was also impaired after Mg depletion. Mg depletion (serum Mg fell 60%) also resulted in significant falls in myocardial [ATP], phosphocreatine (PCr), and Mg with a concomitant rise in myocardial Ca content. These observations are consistent with the tenet that prolonged low [Mg2+]zero can result in marked reduction in oxygen and substrate delivery to the cardiac myocytes, with concomitant changes in membrane phospholipids (potentially resulting in a pro-oxidant state) probably as a result of coronary vasoconstriction.

Glycogen depletion contributes to ischemic preconditioning in the rat heart in vivo.

Ischemic preconditioning depletes the myocardium of glycogen, thus blunting lactic acidosis during subsequent episodes of ischemia. Preconditioning also protects against reperfusion arrhythmias and infarction. To test whether glycogen depletion is necessary for this ischemic tolerance, we preconditioned two groups of intact rats with a series of 3-min coronary artery occlusions. In one group, preconditioning lowered the glycogen concentration of the ischemic region by approximately 50% (24.9 +/- 2.5 to 12.5 +/- 1.8 mumol/g; P < 0.01). In the other, the heart was first loaded with glycogen via glucose-insulin infusion so that preconditioning merely reduced its glycogen concentration back to normal physiological levels. Compared with nonpreconditioned control rats, preconditioned rats with both normal and subnormal glycogen concentrations were protected from reperfusion arrhythmias after a 6-min coronary occlusion (incidence: control rats, 100%; normal glycogen rats, 11%; reduced glycogen rats, 11%). In contrast, only rats with subnormal glycogen concentration after preconditioning exhibited reduced lactate formation and infarct size after a 45-min coronary occlusion [infarct size (percentage of risk area): control rats, 53 +/- 10%; normal glycogen rats, 50 +/- 16%, P = not significant; subnormal glycogen rats, 18 +/- 10%, P < 0.01]. Thus, in the intact rat, myocardial glycogen depletion appears to be necessary for the infarct-limiting, but not for the antiarrhythmic, effects of ischemic preconditioning.

Attenuated Glycogenolysis Reduces Glycolytic Catabolite Accumulation During Ischemia in Preconditioned Rat Hearts

Prior transient episodes of ischemia ("ischemic preconditioning") reduce lactate accumulation and attenuate acidosis during a subsequent prolonged ischemic insult. The mechanisms responsible for attenuated glycolytic catabolite accumulation have not been established but may include earlier exhaustion of glycogen stores, slowed glycogenolysis before complete glycogen depletion, and/or inhibition of glycolysis. Simultaneous repeated measures of myocardial glycogen and the rates of glycolysis, glycogenolysis, glucose utilization, and glycolytic ATP production were obtained during total ischemia by 13C nuclear magnetic resonance spectroscopy in control and ischemia-preconditioned isolated rat hearts. Both [13C]glycolytic and [13C]glycogenolytic rates were significantly lower during total ischemia in preconditioned compared with control hearts (0.77 +/- 0.04 versus 1.06 +/- 0.06 mumol/min per gram wet weight [P < .01] for glycolysis and 0.15 +/- 0.07 versus 0.78 +/- 0.12 mumol/ min per gram wet weight [P < .001] for glycogenolysis, respectively, at 2.5 minutes of ischemia). Slowed glycolysis was present even during the early minutes of ischemia, when significant amounts of available [13C]glycogen were still present. Importantly, the reduction in the rate of glycogenolysis was larger and out of proportion to the reduction in glycolysis and occurred despite an increase in glucose utilization in preconditioned hearts (2.23 +/- 0.15 versus 1.5 +/- 0.10 mumol/min per gram wet weight at 1.25 minutes, P < .01). During early ischemia, conversion of glycogen phosphorylase to the a or "active" form was less in preconditioned than in control hearts (29.1 +/- 2.6% versus 41.2 +/- 9.8%, respectively; P < .05). Taken together, these findings demonstrate that ischemic preconditioning significantly depresses glycolytic catabolite accumulation during sustained ischemia not by more severe glycolytic inhibition or exhaustion of glycogen stores but by depressed glycogenolysis from the onset of ischemia.

Autoregulation of myocardial glycogen concentration during intermittent hypoxia.

During hypoxia, the heart consumes glycogen to generate ATP. Tolerance of repetitive hypoxia logically requires prompt replenishment of glycogen, a process whose regulation is not fully understood. To examine this, we imposed a defined hypoxic stimulus on the rat heart while varying its workload. In intact rats, hypoxia reduced myocardial glycogen approximately 30% and increased both the fraction of glycogen synthase in its physiologically active (GS I) form (from 0.24 +/- 0.06 to 0.82 +/- 0.07; P < 0.005) and glycogen synthesis (from 0.087 +/- 0.011 to 0.375 +/- 0.046 mumol.g-1.min-1; P < 0.005). Reducing cardiac work (with propranolol or heterotopic transplantation) reduced glycogen breakdown, glycogen synthase activation, and glycogen synthesis in parallel, stepwise fashion in intact rats. Correspondingly, hypoxia increased GS I activity in the perfused heart in vitro, but only under conditions where glycogen was consumed. This suggests myocardial glycogen synthase is activated by systemic hypoxia and catalyzes rapid posthypoxic glycogen synthesis. Hypoxic glycogen synthase activation appears to be a proportionate, wholly intrinsic response to local glycogenolysis, operating to preserve myocardial glycogen stores independent of any extracardiac mediator of carbohydrate metabolism.

Contribution of glycogen to aerobic myocardial glucose utilization.

We determined glycogen turnover and the contribution of glycogen as a source of glucose for aerobic myocardial glycolysis and glucose oxidation in parallel series of isolated, working rat hearts subjected to pulse-chase perfusions. Myocardial glycogen of isolated, working rat hearts was radiolabeled, after 30 minutes of substrate-free glycogen depletion, by perfusion for 60 minutes with buffer designed to stimulate resynthesis of glycogen (1.2 mmol/L palmitate, 11 mmol/L [U-14C]- or [5-3H]glucose, 0.5 mmol/L lactate, and 100 microU/mL insulin). Rates of glucose oxidation (14 CO2 production) and glycolysis (3H20 production) were then measured by perfusing the hearts for 40 minutes with buffer designed to simulate physiological conditions (0.4 mmol/L palmitate, 0.5 mmol/L lactate, 11 mmol/L [5-3H]- or [U-14C]- glucose, 100 microU/mL insulin) containing radiolabeled glucose different from that used during resynthesis. During the chase perfusion, rates of glycolysis and glucose oxidation from exogenous glucose were significantly greater than those from endogenous glycogen. Nevertheless, glycogen contributed significantly to myocardial energy production (41% of the overall ATP produced from glucose), and a significantly greater fraction of the glucose from glycogen that passed through glycolysis was oxidized (>50%) compared with the fraction oxidized from exogenous glucose (<20%, P<.05). Myocardial glycogen was simultaneously synthesized and degraded (ie, glycogen turnover) during the chase perfusion, despite net glycogenolysis. Furthermore, enrichment of labeled glucose in glycogen at the end of the chase perfusion, when corrected for newly synthesized glycogen, did not differ from that at the end of the labeling period. Thus, glycogen contributes significantly to aerobic myocardial glucose use under these experimental conditions, and the glucose derived from glycogen is oxidized preferentially compared with exogenous glucose. Additionally, substantial myocardial glycogen turnover occurs, and the manner in which glycogen is degraded does not fit the ordered hypothesis of "last glucose on, first glucose off."

Preconditioning ischemia time determines the degree of glycogen depletion and infarction size reduction in rat hearts

The cardioprotective effect of preconditioning is associated with glycogen depletion and attenuation of intracellular acidosis during subsequent prolonged ischemia. This study determined the effects of increasing preconditioning ischemia time on myocardial glycogen depletion and on infarct size reduction. In addition, this study determined whether infarct size reduction by preconditioning correlates with glycogen depletion before prolonged ischemia. Anesthetized rats underwent a single episode of preconditioning lasting 1.25, 2.5, 5, or 10 minutes of multiple episodes cumulating in 10 (2 × 5 min) or 20 minutes (4 × 5 or 2 × 10 min) of preconditioning ischemia time, each followed by 5 minutes of reperfusion. Then both preconditioned and control rats underwent 45 minutes of ischemia induced by left coronary artery (LCA) occlusion and 120 minutes of reperfusion. After prolonged ischemia, infarct size was determined by dual staining with triphenyltetrazolium chloride and phthalocyanine blue dye. Glycogen levels were determined by an enzymatic assay in selected rats from each group before prolonged ischemia. We found that increasing preconditioning ischemia time resulted in glycogen depletion and infarct size reduction that could both be described by exponential functions. Furthermore, infarct size reduction correlated with glycogen depletion before prolonged ischemia ( r = 0.98; p < 0.01). These findings suggest a role for glycogen depletion in reducing ischemic injury in the preconditioned heart.

Mechanical and metabolic characterization of ischemic contracture in the neonatal pig heart.

Isolated, paced, isovolumetrically beating piglet hearts (n = 37) underwent retrograde aortic perfusion with a crystalloid solution during three periods: 1) baseline (coronary perfusion pressure 60 mm Hg), 2) ischemia (coronary flow 10% of baseline for approximately 80 min), and 3) reperfusion (perfusion pressure returned to baseline). In one group of hearts, glycolysis (using 3H2O formation from [3H]glucose) was assessed. During baseline, peak systolic pressure (PSP) was 101.1 +/- 5.0 mm Hg, end diastolic pressure (EDP) 4.4 +/- 0.5 mm Hg, glycolysis 970.5 +/- 65.3 nmol/min/gwet, and myocardial glycogen 234.8 +/- 12.0 mumol/gdry. During ischemia, PSP decreased to 23.3 +/- 2.7 mm Hg, EDP increased to 12.3 +/- 0.7 mm Hg, myocardial glycogen decreased to 181.5 +/- 30.3 mumol/gdry, and lactate (approximately 154 mumol/gwet) and glycerol (approximately 930 nmol/gwet) were released. Myocardial contracture correlated with a decrease in lactate release. Glycolysis decreased to approximately 400 nmol/min/gwet and remained stable, accounting for approximately 50% of the lactate produced. During reperfusion, PSP recovered to 79.8 +/- 3.5 mm Hg, EDP 6.6 +/- 1.7 mm Hg, and glycolysis 1103.9 +/- 81 nmol/min/gwet. In a second group of hearts, with similar mechanical responses, glucose oxidation (using 14CO2 formation from [14C]glucose) was evaluated. During baseline, glucose oxidation was 165.4 +/- 15.9 nmol/min/gwet and correlated closely (r = 0.957) with mechanical activity. With ischemia, glucose oxidation decreased to approximately 17 nmol/min/gwet, yet accounted for approximately 42% of the ATP produced. Upon reperfusion, glucose oxidation returned to baseline values, but now correlated poorly (r = 0.574) with mechanical activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Superiority of acid extractable glycogen for detection of metabolic changes during myocardial ischaemia

Various methods for extraction and isolation of myocardial glycogen show different yields and identify different glycogen subsets. The aim of the present study was to identify a glycogen fraction exposed to changes during myocardial ischaemia. Endomyocardial biopsies from 10 pigs were sampled before cardioplegia, after cardioplegic arrest, and after reperfusion. Glycogen yields were compared following five extraction procedures: (1) hot alkaline tissue digestion, (2) homogenization in perchloric acid and subsequent determination in homogenate, (3) homogenization in perchloric acid and subsequent determination in supernatant, (4) homogenization in perchloric acid and subsequent determination in the precipitate redissolved in hot alkaline and (5) homogenization in homogenisation buffer with lysating capacity. Glycogen was isolated on filter-paper and determined enzymatically. Hot alkaline tissue digestion yielded the highest glycogen amounts (63.5 +/- 18.3 nmol/mg wet weight). Glycogen yields in perchloric homogenate and supernatant were 51%, perchloric precipitate 47%, and buffer 30% of these obtained with hot alkaline. Glycogen yields in hot alkaline were comparable to the sum of those obtained in perchloric supernatant ("acid extractable glycogen") and redissolved precipitate ("heavily extracted glycogen") confirming that glycogen yields obtained with hot alkaline digestion represent "total glycogen". Acid extractable glycogen showed superior analytical characteristics compared with the other methods. Acid extractable glycogen demonstrated a consistent decrease during ischaemia whereas total glycogen and glycogen extracted in homogenization buffer tended to decrease. Glycogen in perchloric precipitate remained unchanged during ischaemia. These findings support a revival of the concept that tissue contains two forms of glycogen. Decreases in myocardial glycogen content during myocardial ischaemia are best observed with acid extractable glycogen.

706-1 Preconditioning Ischemia Time Determines the Degree of Glycogen Depletion and Infarct Size Reduction in Rat Hearts

Infarct size reduction after ischemic preconditioning has been reported as an all-or-nothing response, with a threshold of 2 to 5 min of preconditioning ischemia time. Furthermore, infarct size reduction is associated with glycogen depletion before prolonged ischemia. We sought to determine whether increasing preconditioning ischemia time results in progressive myocardial glycogen depletion and infarct size reduction and if so, whether infarct size reduction correlates with glycogen depletion before prolonged ischemia. Therefore, ventilated rats underwent a single episode of preconditioning ischemia lasting 1.25 (n = 18), 2.5 (n = 20), 5 (n = 9), or 10 (n = 16) min, or multiple episodes cumulating in 10 (2 × 5 min, n = 17) or 20 (4 × 5 min, n = 13 or 2 × 10 min, n = 14) min of preconditioning ischemia time, all followed by 5 min of reperfusion. Control rats (n = 22) were not preconditioned. In separate groups, glycogen was determined before whereas infarct size was determined after prolonged ischemia (45 min) and reperfusion 120 min). Myocardial glycogen levels and infarct size are shown as a function of preconditioning ischemia time. In addition, infarct size reduction correlated with glycogen depletion before prolonged ischemia (r = 0.98; 19 P &lt; 0.001). Thus, increasing preconditioning ischemia time results in progressive myocardial glycogen depletion and infarct size reduction, reaching a maximal effect when the preconditioning ischemia time is ≥5 min. This maximal effect may be due to marked depletion of myocardial glycogen stores before prolonged ischemia

939-76 The Antiarrhythmic Effect of Ischemic Preconditioning is not Mediated by Myocardial Glycogen Depletion

Reperfusion arrhythmias, a major cause of morbidity and mortality, can be prevented experimentally by preconditioning the heart with ischemia (“ischemic preconditioning” (IP)). While the mechanism responsible for this antiarrhythmic effect is unknown, a leading hypothesis is that IP depletes myocardial glycogen (G), thus limiting anaerobic glycolysis and lactic acidosis during subsequent ischemia. To test this hypothesis, we compared the incidence of sustained (&gt;30 sec) VT or VF during reperfusion in 3 groups of rats (n = 9 each) subjected to a 6-min left coronary occlusion. A control group (CON) received no pretreatment; a preconditioned group (IP) underwent three 2-min coronary occlusions at 5-min intervals prior to the 6-min occlusion; and a third group (GI + IP) received a 40-min infusion of glucose and insulin, to ‘load’ the heart with G, prior to IF’ Additional rats were used to determine the (G) (μmol/g) of the anterior myocardium just before (PRE-G) and just after (POST-G) the 6-min left coronary occlusion, and their difference (G-consumed). Results PRE-G POST-G G-Consumed VT orVF CON 22 ± 3 8 ± 2 14 ± 3 9/9 * IP 15 ± 3 * 10 ± 3 5 ± 2 * 1/9 GI + IP 26 ± 2 12 ± 2 14 ± 4 1/9 * p &lt; 0,05 vs. other groups Thus IP rats had lower myocardial [G] prior to the 6–min coronary occlusion than CON rats, consequently consumed less G during the occlusion, and had a lower incidence of VT or VF on reperfusion. GI + IP rats were equally protected from arrhythmias however, despite pre-ischemic (G), and ischemic G-consumption, similar to CON rats. We conclude that neither the [G] of the myocardium prior to ischemia, nor the quantity of G consumed during ischemia, influence the incidence of reperfusion arrhythmias. This suggests the antiarrhythmic protection conferred by IP is not mediated by myocardial G depletion.

Transient ischemia induces regional myocardial glycogen synthase activation and glycogen synthesis in vivo

Glycogen is consumed during ischemic preconditioning and synthesized during the subsequent period of ischemic tolerance. To better understand this sequence, we examined the effect of brief coronary artery occlusions on regional myocardial glycogen metabolism in intact, anesthetized rats. Sequential 2-min periods of left coronary artery occlusion reduced the glycogen concentration of the anterior left ventricle approximately 30% relative to the posterior region. During subsequent reperfusion, the activity of the physiologically active glycogen synthase I form of glycogen synthase increased threefold in the anterior region (0.58 +/- 0.11 vs. 0.18 +/- 0.08 mumol.g-1.min-1, P < 0.01), stimulating a similar regional increase in glycogen synthesis rate (0.24 +/- 0.04 vs. 0.08 +/- 0.03 mumol.g-1.min-1, P < 0.01). These events were preceded by a rise in regional glucose 6-phosphate concentration, which increased the activity of a myocardial glycogen synthase phosphatase. In diabetic rats glycogen synthase phosphatase activity was significantly lower, and postischemic glycogen synthase activation was significantly impaired. These data suggest the operation of a feedback loop in which transient ischemia leads to a glucose 6-phosphate-mediated increase in the activity of a phosphoprotein phosphatase active toward glycogen synthase. This suggests phospho-protein phosphatase activation may be a feature of the preconditioned myocardium.

Effect of nonworking heterotopic transplantation on rat heart glycogen metabolism.

To determine whether the contractile work history of cardiac muscle influences its responsiveness to insulin, we examined the effect of insulin infusion on glycogen metabolism in the rat heart 1 wk after transplantation into a nonworking heterotopic infrarenal position. Nonworking heterografts had higher basal glycogen concentrations than did in situ working hearts of the same animals (29.9 +/- 2.7 vs. 23.3 +/- 0.8 mumol/g; P < 0.05), and a smaller fraction of their glycogen synthase enzyme activity was in the physiologically active glycogen synthase I form (8 +/- 2 vs. 22 +/- 3%; P < 0.02). During a 25-min infusion of insulin (1 U/min) and glucose (30 mg.kg-1.min-1), the fractional glycogen synthase I activity of heterografts remained lower than that of in situ hearts (29 +/- 5 vs. 56 +/- 7%; P < 0.02) and heterografts synthesized glycogen more slowly (0.126 +/- 0.07 vs. 0.352 +/- 0.06 mumol.g-1.min-1; P < 0.02). These effects could be duplicated by a 24-h fast, which similarly increased myocardial glycogen concentration (to 32.9 +/- 5.6 mumol/g). These observations suggest that the performance of repetitive contractile work is necessary to maintain the myocardium maximally responsive to insulin. Mechanical unloading increases myocardial glycogen concentration, thereby reducing the magnitude of insulin's stimulation of glycogen synthase and consequently the rate of incorporation of circulating glucose into glycogen.

Role of aspirin in modulating myocardial ischemic reperfusion injury.

The role of low-dose aspirin (3 mg/kg, i.v.) in attenuating ischemic reperfusion injury was studied in a canine model. Regional ischemia for 40 min was produced by temporary occlusion of the left anterior descending coronary artery and thereafter reperfusion instituted for 3 h. Mean arterial pressure (MAP), heart rate (HR), left ventricular end diastolic pressure (LVEDP), positive (+) LV dP/dtmax and negative (-) LV dP/dtmax were monitored along with myocardial adenosine triphosphate (ATP), creatine phosphate (CP), glycogen and lactate. Following reperfusion, there was a significant fall in (i) MAP, (ii) (+) LV dP/dtmax and (iii) (-) LV dP/dtmax. LVEDP was corrected after about 2 h of reperfusion. Replenishment of only myocardial CP occurred, without any change in ATP and glycogen, although lactate accumulation was corrected. Aspirin administered 15 min before reperfusion (post-treatment) caused normalisation of LVEDP within 15 min and prevented any deterioration in (-) LV dP/dtmax, although it had no effect on MAP and (+) LV dP/dtmax. After 3 h of reperfusion (post-treatment), myocardial ATP, CP, glycogen and lactate contents became normal. The number of premature ventricular complexes was significantly reduced after aspirin treatment. The present study indicates that low-dose aspirin post-treatment can ameliorate at least some of the deleterious consequences of reperfusion injury of the myocardium.

Report of the subgroup on fetal monitoring

Intrapartum fetal surveillance is still under debate, despite 30 years of clinical experience and numerous clinical trials. Waveform analysis of the fetal electrocardiogram has emerged not as an alternative to cardiotochography but as a support tool to allow more accurate interpretation of intrapartum events. During hypoxia, the healthy fetus is utilizing a series of defense mechanisms. Among these, the increase in sympathetic activity, with an increase in circulating adrenaline, activates the myocardium with an increase in workload (the product of cardiac output, myocardium contractility and blood pressure). If there is an imbalance between myocardial oxygen supply and consumption, determined by the workload, then anaerobic metabolism, with a breakdown of myocardial glycogen stores starts and high T waves emerges. ST depression with negative T waves has recently been observed during hypoxia experiments in experimentally growth retarded guinea pigs whilst their normally grown littermates showed ST elevation. These findings have stimulated the development of a dedicated fetal ECG monitor - STAN - incorporating both standard CTG and ST waveform analysis. The STAN concept has now been taken through the process of recognized validation including several prospective studies and a large randomized trial in Plymouth of 2400 high risk, term deliveries. The T/QRS ratio is only one parameter to be used - equally important is to identify the occurrence of ST depression with biphasic negative T waves and to interrelate the CTG and the ST waveform as outlined in the clinical guidelines (table I). This table contains the clinical experience gained over many years and has formed the basis for the first randomized controlled trial comparing ST waveform + CTG with CTG only. Obviously, when the T/QRS ratio is used as the only component of such a scheme, confusion emerges. The analysis should also contain cases with significant intrapartum hypoxia. Recent findings indicate that only when cord artery pH falls below 7.0 and when there is substantial metabolic acidemia is there a significant risk of intrapartum asphyxia. Metabolic acidemia should be estimated from base deficit in the extracellular fluid and the combination of cord artery and vein data should allow for a more accurate assessment of intrapartum events, including the assessment of the duration of hypoxia. The Plymouth trial has tested the hypothesis that the combination of ST wave form and CTG analysis compared with CTG analysis only would reduce operative interventions for fetal distress without placing the fetus at a risk.(ABSTRACT TRUNCATED AT 400 WORDS)

Glucose-insulin-potassium (GIK) prevents derangement of myocardial metabolism in brain-dead pigs

Brain death is associated with neuroendocrine changes resulting in reduced myocardial glycogen content. The purpose of this study was to investigate the effects of glucose-insulin-potassium (GIK), on myocardial metabolism in brain-dead pigs. Sixteen brain-dead pigs were given GIK infusion (n = 8), or Ringer solution (n = 8). At end-point (7 h post brain death) arterial concentrations and myocardial arteriovenous (a-v) concentration differences of glucose, lactate and free fatty acids (FFA) were assessed, and myocardial biopsy specimens were taken from the right atrium and left ventricle. Biopsies were also taken from five normal pigs. Myocardial glycogen content in the GIK group was significantly higher compared to the control group, but comparable to the non-brain-dead animals. There was a higher and significant myocardial uptake of glucose and lactate in the GIK group compared to the controls. Plasma levels of FFA were significantly lower in the GIK group, and the myocardial uptake of FFA was 5 times higher in the control group compared to the GIK group. There were no significant differences in hemodynamic variables among the groups. In conclusion, intravenous supply of GIK to brain-dead pigs results in increased myocardial glycogen content and seems to prevent abnormal myocardial metabolism, which may have clinical implications for the myocardial protection of donor hearts.

Effects of diabetes on cardiac glycogen metabolism in rats.

The effects of diabetes on myocardial glycogen metabolism in rats were examined and compared with those of fasting. Male Wistar rats were divided into three groups: controls, streptozotocin-induced diabetics, and one-week fasted. Isolated rat hearts were subjected to substrate-free 30-min Langendorff perfusion followed by 60-min working heart perfusion with glucose alone or in combination with insulin or insulin plus beta-hydroxybutyrate (BHB). Myocardial glycogen contents were determined before or 30 min after Langendorff perfusion, or 60 min after working heart perfusion. Before Langendorff perfusion, tissue glycogen concentrations in control, diabetic, and fasted hearts were 3.3 +/- 0.2, 10.0 +/- 0.9, and 5.7 +/- 0.5 (mg/g wet weight), respectively. In diabetic rats, the myocardial glycogen concentration was markedly decreased after working heart perfusion of any of the substrate combinations, even those with insulin and BHB. In contrast, myocardial glycogen in control or fasted rats was not reduced after the addition of glucose with insulin, and/or glucose with insulin and BHB. These results suggest that degradation of tissue glycogen occurs in isolated perfused hearts from diabetic rats, while a clearly different response is shown by fasted hearts.

Effect of early onset angiotensin converting enzyme inhibition on myocardial capillaries.

We investigated the preventive effects of long-term treatment with the angiotensin converting enzyme inhibitor ramipril on myocardial left ventricular hypertrophy and capillary length density in spontaneously hypertensive rats. Rats were treated in utero and subsequently up to 20 weeks of age with a high dose (1 mg/kg per day) or with a low dose (0.01 mg/kg per day) of ramipril. Animals given a high dose of ramipril remained normotensive, whereas those given a low dose developed hypertension in parallel to vehicle-treated controls. At the end of the treatment period, converting enzyme activity in heart tissue was inhibited dose-dependently in the treated groups. Both groups revealed an increase in myocardial capillary length density together with increased myocardial glycogen and reduced citric acid concentrations. Left ventricular mass was reduced only in high dose- but not in low dose-treated animals. Our results demonstrate that early onset treatment with a converting enzyme inhibitor can induce myocardial capillary proliferation, even at doses too low to antagonize the development of hypertension or left ventricular hypertrophy. We hypothesize that potentiation of kinins is responsible for this effect, probably by augmenting myocardial blood flow, which is a well-known trigger mechanism of angiogenesis in the heart.

Regulation of glycogen metabolism in canine myocardium: effects of insulin and epinephrine in vivo.

Myocardial glycogen synthesis and glucose, lactate, and oxygen extraction were measured in the hearts of anesthetized dogs during infusions of insulin and epinephrine. Glycogen was monitored in vivo using 13C-nuclear magnetic resonance during an infusion of [1-13C]glucose into the left anterior descending artery. Glycogen synthesis was observed during a venous infusion of insulin (1.8 microU.min-1.kg-1), and this newly synthesized glycogen was neither broken down nor was more glycogen synthesized during a subsequent epinephrine infusion (0.5 micrograms.min-1.kg-1). During recovery from epinephrine, glycogen synthesis occurred at 2.1 times the rate seen in the control period. Glycogen synthesis was not stimulated in the absence of epinephrine by control infusions of saline. Glucose uptake was increased by insulin during the control period (from 0.09 to 0.39 mumol.min-1.g-1), so that the combined extraction of glucose and lactate exceeded the requirement for oxidizable substrate calculated from oxygen consumption. The "excess" glucose (0.15 mumol.min-1.g wet wt-1) is presumably available for glycogen synthesis. During recovery from epinephrine, lactate uptake was increased over threefold. Because this additional lactate supplies most of the fuel required for oxidation, the excess glucose available for glycogen synthesis during this period was two times that seen before epinephrine (an average of 0.32 mumol.min-1.g wet wt-1 between 20 and 40 min postepinephrine). These data are consistent with the notion that glycogen synthesis can be activated in the heart without an accompanying increase in glucose uptake by providing an alternative substrate (i.e., lactate) for oxidation.

Multiple in vivo full-thickness myocardial biopsies by freeze-clamping.

A technique was developed to permit multiple large biopsies of the in vivo myocardium to measure certain metabolites (ATP, CP, myocardial glycogen, lactate) with minimal chance of ventricular fibrillation or severe alterations in the heart's ability to maintain BP. Adult pigs with normal hearts (n = 9) as well as with hypertrophy (n = 5) created by aortic banding 3-4 months prior were anesthetized, intubated, and ventilated. After a sternotomy, the pericardium was opened and the epicardial surface was cleared of any adhesions. Biopsies were taken from the distal to proximal end of the heart. A suture (3-O Prolene) was placed in a figure-eight pattern in the area to be biopsied. A piece of the myocardium (50-100 mg) was grasped using a pair of narrow dressing forceps and frozen in liquid nitrogen. When the sample was completely frozen, a No. 11 scalpel blade, held at a 90 degrees angle to the epicardium throughout the cut, was used to carve out the full thickness biopsy. The sample was placed immediately in liquid nitrogen. The myocardial defect was repaired by using the previously placed suture buttressed with pieces of subcutaneous fat to prevent tearing the epicardial surface. This in vivo biopsy method has negligible complications and can be repeated or taught with constant reliability.