Myocardial uptake of the fatty acid analog 14-fluorine-18-fluoro-6-thia-heptadecanoic acid in comparison to beta-oxidation rates by tritiated palmitate.

UNLABELLED: The fatty acid tracer 14-18F-fluoro-6-thia-heptadecanoic acid (FTHA) is a metabolically trapped tracer of exogenous fatty acid utilization. The objectives of this study were to determine the relationship of FTHA uptake to changes in perfusion and fatty acid oxidation and to confirm the retention of FTHA in the mammalian heart. METHODS: Six pigs with extracorporeal perfusion of the left anterior descending artery (LAD) and cannulation of the LAD vein were studied. The extraction fraction (EF) of FTHA, measured from LAD arterial and venous blood samples, was compared to beta-oxidation rates, determined by water production from tritiated palmitate. After a baseline period, changes in FTHA EF were measured in 15-min periods of hyperemia, control (baseline flow rate) and lactate infusion. After the lactate infusion, FTHA infusion was terminated, and a 15-min washout period was observed. RESULTS: Beta-oxidation rate was unchanged from the baseline period during the hyperemic and control periods. With lactate infusion, the expected myocardial preference for lactate was noted, with a decline in exogenous fatty acid oxidation. Fluorine-18-FTHA EF paralleled the changes in beta-oxidation, with a decrease in EF during lactate infusion. Increase in perfusion was associated with a decrease in FTHA EF, compared to control, such that the product of flow and extraction was maintained. A linear relationship of FTHA EF to fractional tritiated water production was found. Washout analysis confirmed minimal washout of tracer at 15 min after termination of infusion. Organic solvent extraction of tissue samples suggested that the majority of tissue radioactivity was protein-bound. CONCLUSION: In the extracorporeally perfused mammalian heart, FTHA EF declined during suppression of beta-oxidation with lactate infusion and alteration in perfusion without change in fatty acid oxidation rate. The linear relationship of FTHA EF with fractional water production from tritiated palmitate further confirms a correlation of the uptake of FTHA with fatty acid beta-oxidation rate and supports the utility of FTHA in the noninvasive determination of fatty acid oxidation rate. Furthermore, the trapped nature of the tracer may allow the use of graphical analysis for the quantification of beta-oxidation rates.

The role of glucose metabolism in a pig heart model of short-term hibernation.

Previously, we reported, alterations in glucose metabolism in a 4 day model of chronic coronary stenosis similar to those described in patients with hibernating hearts. The purpose of this study was 2 fold: (1) to identify whether an acute model of mild, sustained ischemia could effect similar changes, and (2) to determine the effects of pharmacological inhibition of glycolysis. In the first group, extracorporeally perfused, intact pig hearts were subjected to 85 min of a 40% reduction in left anterior descending (LAD) coronary arterial blood flow. A second group was subjected to the same protocol, except after 40 min of LAD regional ischemia, iodoacetate (IAA) was administered to block glycolysis. Ischemia reduced MVO2 by 10% in both groups with a further 20% reduction noted following IAA treatment. Regional systolic shortening was reduced nearly 50% by ischemia and decreased an additional 40% following treatment with IAA. Glycolysis was increased by over 700% with ischemia in the first group. IAA caused a 3 fold reduction in glycolysis as compared to the preceding ischemic period and inhibited lactate production. Fatty acid metabolism was significantly reduced by ischemia in the first group, but was not reduced in the IAA group. Activity of creatine kinase associated with myofibrils was reduced and may have contributed to the contractile dysfunction. In conclusion, this acute model of short-term hibernation demonstrates several metabolic changes previously reported in chronic hibernation and may prove useful in determining mechanisms of substrate utilization in simulated conditions of chronic coronary stenosis and hibernation.

Effect of repetitive stunning on myocardial metabolism in pig hearts.

Recent animal and clinical studies have suggested that chronic hibernation, a condition of depressed mechanical function and enhanced glycolysis in viable but downregulated myocardium, may result from chronic repetitive ischemia and reperfusion. The present study was conducted to test whether similar trends could be reproduced in an acute animal preparation of repetitive stunning. Eight intact pig hearts were extracorporeally perfused for 115 min and subjected to four cycles of ischemia [60% decrease in anterior descending flow for 5 min each, interspersed with 15 min of aerobic reperfusion]. Each bout of ischemia caused a progressive decline in regional systolic shortening such that systolic shortening was 37% lower at end-reperfusion (P < 0.05 vs. initial conditions). Regional myocardial O2 consumption was reduced during ischemia but was not significantly lower at end-reperfusion compared with that under initial conditions. Fatty acid oxidation was unchanged at any point during the trials. Although glucose utilization was increased by an average of 264% during the four ischemic periods, it was not significantly or progressively increased during the reperfusion periods. Therefore, although this acute stunning protocol depressed mechanical function, it did not cumulatively increase glycolysis during reperfusion. This absence of accelerated glycolysis is at variance with the metabolic findings reported in clinical hibernation and raises concerns regarding this protocol in animal studies designed to simulate short-term hibernation.

Anaplerotic effects of propionate on oxidations of acetate and long-chain fatty acids.

Studies were performed to test the influence of propionate as a competing myocardial substrate on acetate and palmitate metabolism in reperfused pig hearts after an exposure of mild-to-moderate regional ischemia. Experiments were conducted in intact, working pig hearts (n = 10) using an extracorporeal coronary perfusion technique. Half the animals received 2 mM propionate selectively into the anterior descending (LAD) perfusate. Perfusion conditions in the LAD circulation were divided into three intervals: an aerobic, preischemic period (0-20 min); an ischemic period affected by a 60% reduction in LAD flow (20-60 min); and an aerobic, postischemic period (60-100 min). Steady-state infusions of (1(-14)C) acetate and [9, 10(-3)H] palmitate were begun at 60 min perfusion to monitor metabolism during reperfusion. Propionate had no effect on oxidation of acetate except for a slight delay in CO2 appearance. Propionate significantly suppressed oxidation of long-chain fatty acids (-38 delta %, P < 0.018), which was not explained by a selective scavenging of CoA units or carnitine by propionate, which might otherwise enhance fatty acid activation, transfer, or oxidation. Propionate by indirect estimates had no apparent effect on glucose metabolism. Propionate-treated hearts, despite shifts in substrate preference, were not further compromised in energy metabolism as levels of creatine phosphate and adenine nucleotides were comparable to control hearts. Recovery of regional mechanical function was also comparable between groups but incompletely, with respect to preischemic performance, compatible with myocardial stunning. The data show in reperfused myocardium that propionate is capable of altering the preferred use of fatty acids, but that anaplerotic entry of carbon units during this reperfusion interval was sufficient to prevent a selective imbalance of energy metabolism or deficit in mechanical recovery.

Mechanical and metabolic functions in pig hearts after 4 days of chronic coronary stenosis.

OBJECTIVES: This study sought to evaluate the functional and metabolic consequences of imposing a chronic external coronary stenosis around the left anterior descending coronary artery for 4 days in an intact pig model. BACKGROUND: A clinical condition termed hibernating myocardium has been described wherein as a result of chronic sustained or intermittent coronary hypoperfusion, heart muscle minimizes energy demands by decreasing mechanical function and thus avoids cell death. The use of chronic animal models to stimulate this disorder may assist in establishing causative associations among determinants to explain this phenomenon. METHODS: A hydraulic cuff occluder was placed around the left anterior descending coronary artery in eight pigs. Coronary flow velocity was reduced by a mean (+/- SE) of 49 +/- 5% of prestenotic values, as estimated by a Doppler velocity probe. After 4 days the pigs were prepared with extracorporeal coronary circulation and evaluated at flow conditions dictated by the cuff occluder. Substrate utilizations were described using equilibrium labeling with [U-14C]palmitate and [5-3H]glucose. Results were compared with a combined group of 21 acute and chronic (4 day) sham animals. RESULTS: Four days of partial coronary stenosis significantly decreased regional systolic shortening by 54%. Myocardial oxygen consumption was maintained at aerobic levels, and rest coronary flows were normal. Fatty acid oxidation was decreased by 43% below composite sham values, and exogenous glucose utilization was increased severalfold. Alterations in myocardial metabolism were accompanied by a decline in tissue content of adenosine triphosphate. CONCLUSIONS: These data suggest that chronic coronary stenosis in the absence of macroscarring imparts an impairment in mechanical function, whereas coronary flow and myocardial oxygen consumption are preserved at rest. The increases in glycolytic flux of exogenous glucose are similar to observations on glucose uptake assessed by fluorine-18 2-deoxy-2-fluoro-D-glucose in patients with advanced coronary artery disease. We speculate that intermittent episodes of ischemia and reperfusion are the cause of this phenomenon.

Myocardial kinetics of a putative hypoxic tissue marker, 99mTc-labeled nitroimidazole (BMS-181321), after regional ischemia and reperfusion.

BACKGROUND: A new nitroimidazole complex, 99mTc-propylene amine oxime-1,2-nitroimidazole (BMS-181321), has been developed to allow the positive imaging of hypoxic myocardium by standard gamma camera techniques. METHODS AND RESULTS: To determine the myocardial kinetics of BMS-181321 during myocardial ischemia and reperfusion, seven open-chest swine were prepared according to a model of extracorporeal coronary perfusion in which left ventricular wall thickening (percent end-diastolic thickness) and substrate use in the left anterior descending (LAD) region ([14C]palmitate and [3H]glucose infusions) were determined. Measurements were obtained at baseline, during 40 minutes of ischemia produced by reducing flow in the LAD distribution by 60%, and during 70 minutes of reperfusion. Three aerobic control hearts were also studied in which LAD blood flow was not reduced. Regional coronary circulation was further assessed in all hearts by use of radiolabeled microspheres injected during ischemia. BMS-181321 (20 to 30 mCi) was injected after 30 minutes of ischemia, and its myocardial uptake was assessed by dynamic planar gamma imaging. Ischemia was associated with declines in fatty acid metabolism (15 +/- 11 mumol.h-1.g dry wt-1, mean +/- SEM), systolic wall thickening (20 +/- 6%), and myocardial oxygen consumption (3 +/- 1 mL.min-1.100 g-1) and an increase in exogenous glucose utilization (75 +/- 13 mumol.h-1.g dry wt-1). Systolic wall thickening recovered by only 8 +/- 3% with reperfusion. Initial distribution of BMS-181321 in the aerobic hearts appeared homogeneous. Washout from the ischemic and reperfused LAD bed was slower than the aerobically perfused LAD bed in the control group (t1/2 = 136 +/- 1 versus 80 +/- 1 minutes, P < .05), allowing visualization of the LAD region during reperfusion. Tissue activity of BMS-181321 was inversely related to LAD blood flow during ischemia (r = -.68 +/- .05), and the ratio of BMS-181321 in the LAD region versus normal myocardium was 1.7 +/- 0.2. Control swine lacked regional deposition of the tracer in the normally perfused LAD distribution. CONCLUSIONS: Thus, acute regional ischemia in these studies was visualized as an increase in retention of BMS-181321, suggesting its applicability in the imaging of clinical conditions of myocardial hypoperfusion.

Effects of moderate repetitive ischemia on myocardial substrate utilization.

The purpose of this report was to directly measure the influence of antecedent ischemia or repetitive ischemia on subsequent rates of intermediary metabolism, specifically exogenous glucose utilization and fatty acid oxidation, with the use of myocardial equilibrium labeling with [U-14C]palmitate and [5-3H]glucose. Twenty-one intact, working, extracorporeally perfused pig hearts were prepared and divided into three groups. These groups included 7 control hearts and 14 comparison hearts, which were exposed to either one cycle (cycle 1, n = 7) or four cycles (cycle 4, n = 7) of brief (5-10 min), moderate (70% decrease in flow below aerobic values) precursory ischemia to the left anterior descending (LAD) circulation followed by aerobic reperfusion. All groups then underwent a 40 min sustained LAD ischemia (60% decrease in flow below aerobic levels) and 40 min aerobic reperfusion. Treatment with one cycle of transient ischemia did not significantly modify the pattern of glycolytic flux from control values during sustained ischemia (over a ninefold increase in average control and cycle 1 values above aerobic levels). However, repetitive ischemia in cycle 4 hearts demonstrably attenuated glycolytic flux during the same interval (-45% from control hearts, P < 0.046). Glucose utilization rapidly returned to near-aerobic values in all three groups during reperfusion but was again appreciably lower (P < 0.004 from control values) in cycle 4 hearts. Fatty acid oxidation averaged 12.3 +/- 1.2 mumol.h-1.g dry wt-1 in all three groups during sustained ischemia and 21.3 +/- 2.0 mumol.h-1.g dry wt-1 during reperfusion (not significant among groups for either perfusion interval).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial function and metabolism in pig hearts after relief from chronic partial coronary stenosis.

Metabolic behavior was compared during acute extracorporeal reperfusion after removal of a chronic 4-day partial coronary stenosis in eight pig hearts (RCS group) and during comparable extracorporeal perfusion in seven chronically prepared hearts (Sham group). Coronary stenosis in RCS hearts was induced in the left anterior descending (LAD) artery by partial inflation of a hydraulic occluder to restrict LAD peak phasic velocity by approximately 50%. Regional mechanical shortening was decreased in RCS compared with Sham hearts after 4 days of chronic coronary stenosis [diminished systolic shortening (P < 0.066) with systolic expansion (P < 0.015)] but was comparable to Sham hearts after relief from stenosis. At analogous workloads (left ventricular pressure and heart rate) during reperfusion, metabolic behavior was distinctive between groups. Specifically, compared with Sham hearts, myocardial O2 consumption was selectively increased in RCS hearts (+ 49 delta %, P < 0.026) as was fatty acid oxidation estimated from 14CO2 production from [U-14C]palmitate (+ 60 delta %, P < 0.061) and exogenous glucose utilization measured from the release of 3H2O from [5-3H]glucose (+ 517 delta %, P < 0.025). At the conclusion of the studies, triphenyltetrazolium chloride staining showed no gross evidence of macroinfarction in RCS or Sham hearts, and there was an essentially unremarkable histological survey of anterior myocardium for microscopic necrosis in either group. The level of O2 consumption and preservation of preferred fatty acid utilization indicate that metabolism remains or regains its aerobic pattern of activity in early recovery immediately after removal of chronic partial coronary stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial metabolism in chronic reperfusion after nontransmural infarction in pig hearts.

The purpose of these studies was to evaluate metabolic behavior in a 4-day reperfusion model in pigs after induction of subendocardial infarction. Two groups of swine [sham and intervention (Int) groups, n = 7) and 10 hearts per group, respectively] were prepared comparably with two surgical procedures separated over 4 days. In the Int group at the time of the first surgery, coronary flow in the left anterior descending (LAD) circulation was partially restricted (by 60%) for 60 min and was then reperfused. LAD myocardium at the time of the second surgery in both groups was extracorporeally perfused aerobically (5.9 +/- 0.2 ml.min-1.g dry wt-1) for 60 min and infused by equilibrium labeling with [U-14C]-palmitate and [5-3H]glucose to estimate fatty acid oxidation and exogenous glucose utilization. During extracorporeal perfusion, regional myocardial shortening and oxygen consumption were comparable between groups despite a marginal impairment in ATP resynthesis by mitochondria (26% decrease, P < 0.071) in Int hearts and a significant decline in mitochondrial respiration (45% decrease in respiratory control rate, P < 0.008; and 41% decrease in state 3 respiration, P < 0.032) as compared with sham hearts. Fatty acid oxidation described by 14CO2 production was 34.00 +/- 4.72 mumol.h-1.g dry wt-1 (averaged from 30-60 min of perfusion) in sham hearts but was decreased (by 48%, P < 0.004) in Int hearts. This reduction in fatty acid utilization may in part be explained by declines in the observed activity of the mitochondrial membrane transporter enzyme, carnitine palmitoyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid kinetics in aerobic myocardium: characteristics of tracer carbon entry and washout and influence of metabolic demand.

These studies evaluated the kinetics of tracer uptake and washout after step-function labeling with 14C-palmitate. Washout and uptake function curve analysis for total radioactivity (TR) was derived according to the expressions: TR = Fx integral of 0 infinity C(t) x dt and TR = Fx integral of 0 infinity (Css - C(t)) x dt, respectively, with Vc = TR/Ca, where F = coronary flow; Css = steady-state concentration; C(t) = concentration with respect to time; Ca = arterial concentration; and Vc = distribution volumes within the fatty acid pathway. The only radioactive metabolites in venous effluent were fatty acids and 14CO2. The estimated Vc of fatty acids was small (1.2-1.7 ml/g dry wt or 0.4-0.5 mumol/g dry wt) and compatible with labeled substrate trapped in the blood volume. The Vc of 14CO2 was much larger (11.4-15.8 ml/g dry wt or 3.6-4.2 mumol/g dry wt) and correlated with counts contained in the aqueous soluble and fatty acid fractions in tissue. The counts in tissue were distributed between the aqueous soluble fraction (40%), which was rapidly depleted during washout, and a lipid fraction (60%) (triacylglycerols and phospholipids), which was resistant to washout. Distributions in tissue radioactivity between the aqueous soluble and lipid fractions support the notion of a dual pathway in fatty acid oxidation, one arm of which passes through the resident pool of triacylglycerols, which has a long time constant. The presence of this pool may impart an error in estimating fatty acid oxidation by external labeling techniques.

Correlation between [5-3H]glucose and [U-14C]deoxyglucose as markers of glycolysis in reperfused myocardium.

Studies were conducted in extracorporeally perfused, intact, working pig hearts to determine whether, in heart muscle, trace-labeled deoxyglucose serves as an accurate marker of glycolytic flux in reperfusion after exposures to mild to moderate regional ischemia. In the main study, two groups of hearts were compared, as distinguished by levels of glucose in the whole-blood perfusate (euglycemic hearts [group I], blood glucose of 7.4 +/- 0.2 mumol/ml, n = 7; hyperglycemic hearts [group II], blood glucose of 12.9 +/- 0.5 mumol/ml, n = 8). Both groups were subjected to a 60% reduction in anterior descending coronary flow for 30 minutes followed by reperfusion for 40 minutes. Modest and comparable regional mechanical stunning during reflow was noted in both groups. Glucose utilization, as estimated from the release of 3H2O from the steady-state infusion of [5-3H]glucose during aerobic perfusion, was modest but during reperfusion was noted to increase significantly above aerobic values in each of the two groups, with a doubling of rates in group II hearts compared with group I hearts (p less than 0.041 or p less than 0.090). Net lactate extraction was comparable in reflow in both groups, suggesting in this specific instance a preferential enhancement of glucose oxidation in hyperglycemic group II hearts. Shifts in accumulation of tissue radioactivity of [U-14C]2-deoxyglucose in reperfused myocardium were not able to track these trends. The variability of 14C-labeled radioactivity among animals was marked and essentially masked any ability to discern trends in glycolysis as described by tritiated glucose between the aerobic and reperfusion intervals. When the data were arrayed by linear regression analysis, the slopes derived from 14C-labeled deoxyglucose were either discordant or insensitive to those described by 3H-labeled glucose. Tissue glycogen levels were slow to recover in early reflow and at end reperfusion were still significantly depressed from aerobic levels. The present data indicate that coronary reperfusion and hyperglycemia have influence in determining glycolytic flux in myocardium. Labeled deoxyglucose, considered solely as a marker of exogenous glucose utilization, appears to be an insensitive agent in describing these events at conditions of relatively low glucose flux.

An animal model of chronic coronary stenosis resulting in hibernating myocardium.

An experimental animal model of hibernating myocardium is presented. Sixteen animals were initially prepared of which seven were selected for final review. Hearts were instrumented in two separate surgical procedures such that maximum phasic flow velocity in the left anterior descending (LAD) coronary artery was reduced by 50% and followed over 1 wk. Regional shortening declined at 1 wk to 62% of aerobic values (P less than 0.048) and did not improve over 2 h reperfusion. Metabolic determinations, obtained after 1 wk of coronary stenosis and immediately sampled before and after release of the LAD flow constrictor, showed no evidence of acidosis, hypercarbia, or an inability to extract oxygen at the tissue level. Thereafter, during the 2-h reperfusion period, hearts were able to respond to dobutamine (10 micrograms/kg infusion over 1 min) challenge with an appropriate shift in an end-systolic length estimate of contractility. Mitochondrial respiration at the conclusion of the studies in the reperfused bed demonstrated near normal recovery compared with aerobic values. None of the seven hearts showed gross evidence of infarction and only one heart was noted to have a few microfocal changes of healing infarction. Thus a new model of coronary stenosis is presented, which affected substantial reductions in mechanical function consistent with the concepts of hibernating myocardium. These mechanical events were not associated with marked metabolic abnormalities, reflecting advanced ischemia or mitochondrial dysfunction and could be transiently improved with inotropic stimuli. This model may prove beneficial as a tool in understanding mechanistic events underlying the hibernating heart.

Effects of propionyl-L-carnitine in chronically hypoperfused ("hibernating") myocardium.

The purpose of this report was to test the effects of systemic treatment with propionyl-L-carnitine in a new model of chronically hypoperfused ("hibernating") myocardium. Adolescent swine were instrumented to undergo a period of mild partial coronary constriction for 1 week (50% reduction of the maximum phasic flow velocity in the anterior descending coronary artery). This reduced regional mechanical function by 56%. The system satisfied criteria defining "hibernating" myocardium, in that the chronic hypoperfusion did not produce massive tissue necrosis and that the reduction in regional contraction remained responsive to inotropic stimulation. Treatment with 50 mg/kg propionyl-L-carnitine by mouth twice daily for 1 week significantly (p less than 0.0005) increased concentrations of free and total carnitine in the myocardial tissue by 39% and 31%, respectively. Treatment with propionyl-L-carnitine did not alter regional systolic shortening in either hibernation or reperfusion for 2 hours, but enhanced one estimate of contractility reserve based on the rate of left ventricular emptying with occlusion of the inferior vena cava. Propionyl-L-carnitine did not reverse the observed impairments in mitochondrial respiration (diminutions in state 3 respiration and the respiratory control ratio), but limited the number of lesions seen on histological examination. Six out of eight placebo hearts showed one or more changes of ischemia, infarction or reperfusion injury, while the same was true in only two out of eight hearts treated with propionyl-L-carnitine (p less than 0.003). Carnitine and various analogues have been proposed to benefit ischemic myocardium. The present data suggest that this general sparing effect may also occur with the propionyl derivative in chronically underperfused myocardium.

Distribution of carbon flux within fatty acid utilization during myocardial ischemia and reperfusion.

Twenty-nine intact, working pig hearts were extracorporeally perfused and divided into two study groups (16 Aerobic and 13 Ischemic/Reflow hearts). Step function, equilibrium labeling with [14C]palmitate was used to develop uptake and washout curves of radioactive fatty acid products contained in coronary effluent during either aerobic perfusion or reperfusion after ischemia (60% reduction in left anterior descending coronary flow for 30 minutes). Left anterior descending control flows were slightly overperfused in Aerobic hearts (18% higher than in Ischemic/Reflow hearts); otherwise, circumflex and right coronary flows, left ventricular pressure, and serum fatty acids and blood sugar levels were comparable between groups. As expected in Ischemic/Reflow hearts, recovery of regional systolic shortening and myocardial oxygen consumption in reperfusion was only modestly impaired (-20% and -19%, respectively, not significant and p less than 0.011 compared with preischemic values, not significant from Aerobic hearts). The only significant metabolized product to be released from labeled fatty acid utilization in either group was 14CO2. A smaller fatty acid pool also was measured and accounted for by that contained in the coronary intravascular volume. We could determine no significant back diffusion of fatty acids from myocardium in either perfusion condition. Uptake time constants of the early phase of 14CO2 production also were virtually identical in both groups (19.9 +/- 3.2 versus 16.7 +/- 3.2 minutes in Aerobic and Ischemic/Reflow hearts, respectively) and strongly correlated with hemodynamics as described by heart rate. In washout studies, tissue radioactivity in the aqueous soluble and fatty acid pools declined in both study groups, and counts in complex lipids and cholesterol/cholesteryl esters remained steady, whereas those in triacylglycerols varied. Washout of 14CO2 in both groups never reached background radioactivity over a 40-minute sampling after cessation of isotope infusion into the perfusate, suggesting slow release of trapped substrate from intracellular pools, which then proceeded to fatty acid oxidation. In conclusion, these experiments have demonstrated very similar findings with respect to fatty acid uptake, storage, and release characteristics between aerobic and reperfused myocardium. We found no differences in preferred substrate utilization and oxidation as a result of reversible ischemia followed by reflow.

The effects of pantothenic acid, cysteine and dithiothreitol in intact, reperfused pig hearts.

The objective of this study was to augment myocardial tissue levels of amphiphiles using a treatment protocol of pantothenic acid, cysteine and dithiothreitol (DTT) in 24 hr fasted pigs and to test their influence on mechanical recovery in reperfusion. Eighteen pig hearts were extracorporeally perfused aerobically, subjected to regionally reversible ischemia in the left anterior descending perfusion system and reperfused. Nine hearts served as a placebo group; nine hearts were treated. All hearts received trace-labeled palmitate to measure fatty acid oxidation and were perfused with an infusion of 20% Intralipid to augment perfusate levels of fatty acids. Fasting alone in the presence of carbon substrates in the coronary perfusate was not sufficient to de-inhibit pantothenic acid kinase such that CoA synthesis was not enhanced. Tissue contents of triacylglycerols and phospholipids in reperfused myocardium were no different than in aerobic heart muscle but free CoA and free and total carnitine were reduced, suggesting a leakage of cytosolic contents across injured sarcolemma. Treatment significantly impaired mechanical recovery during reflow, presumable due to the noxious properties of DTT whose reported effects in heart muscle are wide ranging, difficult to predict in intact hearts and may be harmful.

Measurement of phasic velocities in vessels of intact freely beating hearts.

The study of flow dynamics on the coronary microcirculation of the intact beating heart has been greatly hampered by the thickness of the tissue and its continual movement. Using fluorescent microspheres and video-image processing, we have devised a means to measure an index of blood velocities. Measurements were made on open-chest anesthetized cats without any artificial restraints to the heart motion. However, advantages exist for minimizing mechanical motion, therefore, a heart holder based on a vacuum concept, along with modified versions of previously demonstrated methods, were tested. Results showed that the vacuum holder provided more restraint to epicardial motion than the pericardium alone, and despite large differences in epicardial motion between the two, overall flow measurements of the microspheres were comparable. Other methods of immobilizing the heart usually did not yield normal flow velocities. This video analysis method allows for the reproducible measurement of particle velocities at time points throughout the cardiac cycle. In keeping the normal heart dynamics intact, more realistic results from the study of coronary blood flows can be obtained.

Effects of propionate on mechanical and metabolic performance in aerobic rat hearts.

The purpose of this report is to describe the contribution of propionate as an adjunct source of oxidative metabolism in aerobic myocardium. In the first series of studies, six groups of isolated working rat hearts (n = 6-8 per group) were perfused for 40 minutes with Krebs-Henseleit media containing 11 mM glucose. Propionate treatment was provided to the media at a constant dose per heart group and extended over a range of dosages, including: 0 (placebo control), 0.1, 0.5, 1.0, 5.0, and 10.0 mM, buffered to pH 7.4. Average aerobic coronary blood flow for all groups was 21.5 +/- 0.6 ml/min; average left ventricular peak systolic pressure was 123.7 +/- 1.4 mmHg. There were no significant differences among groups compared with placebo hearts for aortic flow, heart rate x aortic pressure product, or myocardial oxygen consumption, although performance tended to decline in the 10 mM group. A clear dose-response relationship was observed in 14CO2 production from labeled propionate, with a 12-fold increase between the 0.1 and 10 mM groups. Most of the increase occurred at the lower dosages, with a relative leveling off at the 1.0, 5.0, and 10.0 mM doses. In part 2, propionate was examined as a sole substrate. At 1.0 mM without glucose, propionate per se was unable to support mechanical function over the course of the perfusions, but still maintained high rates of oxidation, comparable to that of the 1.0 mM group with glucose in part 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical and metabolic determinants of myocardial stunning in extracorporeally perfused pig hearts.

The purpose of this study was to apply step-wise multiple linear regression analysis retrospectively to an array of mechanical and metabolic measurements chosen because they had the potential to predict the extent of contractile recovery from a prescribed duration of myocardial ischemia. Data were acquired from the extracorporeally perfused, intact, working pig heart which was rendered regionally ischemic (60% reduction in anterior descending coronary flow) for 45 minutes and reperfused to aerobic levels for a final 30-50 minutes. Mechanical recovery was defined by the percentage systolic shortening and the area circumscribed by left ventricular pressure-segment length loops. Data were taken from 39 control hearts and from 16 hearts treated with oxfenicine, an agent which we have previously used to alter mechanical function by its interference with fatty acid metabolism. Despite the fixed nature of the protocol in affecting ischemic hypoperfusion, a wide range of mechanical responses encompassing hypo- and dyskinesis was produced during ischemia, followed by mechanical stunning during reflow. Of the parameters surveyed, regional indices of mechanical performance, together with perfusate pH and PCO2, best predicted recovery. Along with the heart rate, these predictors gave correlations of 0.875 for percentage systolic shortening and 0.766 for the length-pressure loop in control hearts. The analyses were also sensitive to the influence of pharmacological intervention with oxfenicine in that several parameters lost statistical significance for percentage systolic shortening and two were added (heart rate and end-diastolic length) for the length-pressure loop. Separate statistical models for oxfenicine-treated hearts gave correlations of 0.905 for percentage systolic shortening and 0.915 for the length-pressure loop. The data suggest that step-wise multiple linear regression analysis provides new insights toward our understanding of the mechanisms of mechanical stunning in myocardial reperfusion.

Mechanisms of substrate preference for oxidative metabolism during early myocardial reperfusion.

We previously reported in working swine hearts a preferred use of fatty acids during early myocardial reperfusion. The purpose of these studies was to test whether this pattern of substrate oxidation was the result of excess energy demands during mechanical recovery. Two groups of pig hearts (n = 15) were compared. Both received Intralipid with heparin (serum fatty acids, 1.02 +/- 0.05 mumol/ml) to ensure preferred substrate availability and both received [2-14C]pyruvate to monitor myocardial use of a carbohydrate substrate. In one group (n = 8) oxfenicine was administered to suppress fatty acid utilization. Left anterior descending (LAD) coronary flow was maintained at aerobic levels for 30 min, reduced by 60% for 45 min, and restored to aerobic levels for a final 50 min. Ischemia caused the expected decreased in global and regional mechanical performance. Recovery in motion during reflow was less in oxfenicine-treated hearts (73 vs. 32% decrease in systolic shortening from aerobic values in treated and control hearts, P less than or equal to 0.01 and P less than or equal to 0.05, respectively). Pyruvate oxidation declined dramatically in both groups during ischemia but recovered disparately. In control hearts CO2 production remained depressed during reperfusion (NS from ischemic values), whereas in treated hearts it increased 5.5-fold (but did not exceed aerobic values). Tissue levels of acetyl CoA and acetylcarnitine were not statistically different between perfusion beds (aerobic vs. reperfusion) within groups. Oxfenicine reduced levels of acetyl carnitine in both perfusion beds.(ABSTRACT TRUNCATED AT 250 WORDS)

Time dependence of regional systolic left ventricular relationships in intact hearts.

In intact hearts the beat-to-beat left ventricular systolic pressure-length relationship is not uniquely defined, but rather is history dependent and appears hysteretic. The purpose of these studies was to assess the time course of this phenomenon. In an open chest swine heart preparation, left ventricular pressure, regional lengths, and wall thickness were measured. Loading conditions were altered by the infusion of volume into the left ventricle to increase peak systolic pressure approximately 30 mmHg. The resultant interbeat systolic pressure-dimension relationships were hysteretic. The first part of the study (n = 13) was to test whether the myocardium exhibited a long-term memory of prior mechanical events. Measurements obtained 30 and 120 s after volume loading revealed no residual differences in pressure or dimension compared with preinjection values. Thus the phenomenon was transient and complete (reversible) by 30 s. To better characterize this event, the temporal effects of myocardial loading were studied (n = 8). A randomized comparison of two different rates of volume infusions (27 +/- 2 vs. 56 +/- 2 ml/s, P less than 0.001) was performed. Varying the volume loading resulted in similar increases in peak left ventricular pressure (35 +/- 3 vs. 31 +/- 3 mmHg) but at different increments of development, i.e., greater than 5-7 cardiac cycles at the slower rate of volume infusion vs. greater than 2-3 cardiac cycles (P less than 0.001) at the faster rate. The isochronal systolic pressure-dimension relationships were quantitated by measuring the area of the hysteretic relationship and its slope.(ABSTRACT TRUNCATED AT 250 WORDS)