Metabolism of the human heart. II. Studies on fat, ketone and amino acid metabolism

Glucose-insulin-potassium infusion in acute myocardial infarction. Review of clinical experience

A solution of 300 gm of glucose, 50 units of regular insulin, and 80 mEq of potassium chloride in 1,000 ml of sterile water infused at a rate of 1.5 ml/kg of body weight per hour can alter the availability of glucose and free fatty acids to the myocardium. Clinical studies of patients receiving this infusion less than 15 hours after the onset of symptoms of acute myocardial infarction suggest a reduction in mortality, an improvement in left ventricular mechanical performance, and a reduction in cardiac irritability as beneficial effects. Swan-Ganz catheterization for hemodynamic, electrophysiologic, and metabolic monitoring is recommended. Diabetics who require insulin and patients with impaired renal function are not candidates for the infusion. Further clinical studies are required before conclusions can be reached regarding the efficacy of glucose-insulin-potassium infusion in attempts to salvage damaged myocardium.

Effect of sodium salicylate and acetylsalicylic acid on epicardial ST-segment elevation during coronary artery occlusion in dogs

The effect of sodium salicylate and acetylsalicylic acid (ASA) on myocardial ischaemic injury following acute coronary artery occlusion has been studied in thoracotomized dogs during basal conditions and during elevation of plasma free fatty acid (FFA) concentration induced by intravenous (i.v.) infusion of isoprenaline (0.075-0.15 microgram/kg/min). Ischaemic injury was measured as the sum of ST-segment elevations (sigmaST) in epicardial ECG recordings from 10-15 sites 15 min after occlusion. Both sodium salicylate and ASA (60 mg/kg) significantly reduced sigmaST both before and during isoprenaline infusion. Arterial concentrations of FFA were reduced by either drug during isoprenaline infusion, whereas in the basal state only a significant effect by sodium salicylate could be demonstrated. The reduction in epicardial ST-segment elevation during coronary occlusion could not be explained by reduced mechanical activity of the heart. It is suggested that the reduction by salicylates of myocardial ischaemic injury might be related to reduced utilization of FFA by the myocardium, although a FFA-nondependent mechanism cannot be excluded in the basal state.

Influences on the efficiency of cardiac work

The efficiency of cardiac work measured in isolated guinea pig atria can be influenced by change of the heart rate or the stroke work due to electric stimulation or drug actions: An increased cardiac performance caused by enhanced heart rate needs considerably more oxygen than an increase of the total cardiac work to the same degree due solely to a positive inotropic action. Oxidation of long and short chain fatty acids lowers the efficiency of cardiac work connected with negative inotropic effects. An increase of the heart rate is followed by a shift to the oxidation of carbohydrates, at rest to the oxidation of FFA. Long chain fatty acids are not sufficient for the increased demand of energy in the cardiac muscle at high heart rates and are then poorly oxidized. The problems connected with the Ca++ binding of FFA in the cardiac cytoplasm after inhibition of their oxidation well be discussed.

Reduction of hospital mortality rate of acute myocardial infarction with glucose-insulin-potassium infusion

Free fatty acids (FFA), the predominant myocardial energy substrate, are present in increased quantities immediately following acute myocardial infarction (AMI) and may cause deleterious alterations in cardiac rhythm, oxygen consumption, and mechanical performance. In an attempt to suppress FFA and simultaneously increase the availability of carbohydrate as a myocardial substrate, 70 patients with unequivocal AMI were administered a right atrial infusion of glucose-insulin-potassium (GIK) (300 gm. of glucose, 50 U. of regular insulin, and 80 mEq. of KC1 per liter of H2O) at a constant rate of 0.5 to 2.0 ml. per kilogram per hour for 48 hours. A dramatic fall in FFA (944 +/- 57 to 289 +/- 16 muEq per liter, p less than 0.0005) occurred during GIK infusion, and FFA rebounded to 420 +/- 39 muEq per liter (p less than 0.005) when GIK was discontinued. The hospital mortality rate in the 70 GIK recipients was compared to that of 64 untreated patients (controls) from the same coronary-care unit during the previous year. GIK and control groups had similar severity of infarction as assessed by prognostic scales of Killip, Peel, and Norris, respectively. The hospital mortality rate was reduced in the GIK recipients compared to the control group (11/70 vs. 19/64, p less than 0.05). In patients without history of prior myocardial infarction, the mortality rate was reduced four-fold in GIK recipients compared to controls (6 vs. 24 per cent, p less than 0.05). Complications of GIK infusion were infrequent and included chiefly hyperglycemia and hyperkalemia, both of which dictated meticulous monitoring of serum chemistries. The data suggest that suppression of plasma FFA with GIK infusion may be associated with a significant reduction in the hospital mortality rate of acute myocardial infarction.

Free fatty acid oxidation by forearm muscle at rest, and evidence for an intramuscular lipid pool in the human forearm

The objects of these experiments were to determine to what extent oleic acid, removed from plasma by forearm muscles, was oxidized immediately, and to search for evidence of an intramuscular lipid pool which may be composed to triglycerides synthesized from plasma free fatty acids and which may supply substantial portions of lipid substrates for oxidation by muscle. To these ends (1-14C]oleic acid was infused at constant rate into the brachial artery of seven healthy young men at rest in the postabsorptive state. Results were: (1) muscle respiratory quotient (0.76) implied that about 80% of the oxygen consumed was for the oxidation of lipid. (2) Muscle free fatty acid uptake, had it been oxidized directly, could account for more than 100% of observed oxygen uptake. (3) There was a lag of at least 30 min before 14CO2 appeared in forearm venous blood. (4) 14CO2 release from forearm muscle tended to reach an apparent plateau after 3 h of infusion of [14C]oleic acid. (5) During the time of plateau 14CO2 release, oleic acid extracted from plasma could account for only 20% of oxygen consumption; most of the oleic acid taken up was not oxidized directly. (6) 14CO2 release persisted at a high level during the 1-3 h follow-up period after the infusion ended. (7) Neither the delay in initial appearance of 14CO2 nor its continued release after cessation of infusion was due to delay and distribution in a forearm CO2 pool, since intra-arterial infusion of NaH14CO3 in additional subjects demonstrated much more rapid distribution of 14CO2 in the forearm. Results show that most, if not all, free fatty acids taken up by resting muscle are not oxidized directly, but probably enter an intramuscular pool which has a slow turnover during resting metabolism and is the immediate source of oxidized lipid substrate.

Effects of cortisol on cultured rat heart cells: lipase activity, fatty acid oxidation, glycogen metabolism, and ATP levels as related to the beating phenomenon

This paper reports the determination of the ability of rat heart cells in culture to release [(14)C]palmitate from its triglyceride and to oxidize this fatty acid and free [(14)C]palmitate to (14)CO(2) when the cells are actively beating and when they stop beating after aging in culture. In addition, the levels of glucose, glycogen, and ATP were determined to relate the concentration of these metabolites with beating and with cessation of beating. When young rat heart cells in culture are actively beating, they oxidize free fatty acids at a rate parallel with cellular ATP production. Both fatty acid oxidation and ATP production remain constant while the cells continue to beat. Furthermore, glucose is removed from the growth medium by the cells and stored as glycogen. When cultured cells stop beating, a decrease is seen in their ability to oxidize free fatty acids and to release them from their corresponding triglycerides. Concomitant with decreased fatty acid oxidation is a decrease in cellular levels of ATP until beating ceases. Midway between initiation of cultures and cessation of beating the cells begin to mobilize the stored glycogen. When the growth medium is supplemented with cortisol acetate and given to cultures which have ceased to beat, reinitiation of beating occurs. Furthermore, all decreases previously observed in ATP levels, fatty acid oxidation, and esterase activity are restored.

Effects of glucagon on myocardial metabolism in patients with and without coronary artery disease

The metabolic effects of glucagon on the heart were studied in subjects with and without coronary artery disease. In both groups, a moderate rise in the arterial glucose level occurred with practically unchanged glucose uptake by the myocardium. Myocardial oxygen extraction was also unchanged in both groups of subjects. In individuals with normal coronary arteries, myocardial extraction ratio of lactate was normal before and unchanged after glucagon administration. In patients with significant coronary artery disease, mean extraction ratio of lactate was very low before glucagon and increased markedly following its administration. Seven of 18 patients had production of lactate by the myocardium before glucagon, and this reverted to lactate extraction 5 min after glucagon administration. Left ventricular work index was found to increase more than indices of myocardial contractility and oxygen consumption, and improved aerobic lactate utilization during glucagon action may be partly related to the lower oxygen cost of work performance or improved cardiac efficiency. Arterial serum potassium level decreased in both groups of subjects after glucagon administration, with the appearance of a slightly negative potassium balance across the myocardium. The possible relationship of the cardiac inotropism induced by glucagon to intramyocardial ionic exchanges is discussed.

Free fatty acid metabolism of the human heart at rest

Myocardial substrate metabolism was studied in 13 subjects at the time of diagnostic cardiac catheterization by means of palmitic acid-(14)C infusion with arterial and coronary sinus sampling. Two subjects were considered free of cardiac pathology and all, with one exception, demonstrated lactate extraction across the portion of heart under study. Data for this single lactate-producing subject were treated separately.The fractional extraction of (14)C-labeled free fatty acids (FFA) (44.4+/-9.5%) was nearly twice that of unlabeled FFA (23.2+/-7.8%) and raised the possibility of release of FFA into the coronary sinus. FFA uptake, based on either the arterial minus coronary sinus concentration difference or the FFA-(14)C fractional extraction, was directly proportional to the arterial FFA concentration. Gas-liquid chromatography failed to demonstrate selective handling of any individual FFA by the heart. Fractional oxidation of FFA was 53.5+/-12.7%, accounting for 53.2+/-14.4% of the heart's oxygen consumption while nonlipid substrates accounted for an additional 30.0+/-17.3%. Determinations of both labeled and unlabeled triglycerides suggested utilization of this substrate by the fasting human heart. Direct measurement of FFA fractional oxidation as well as FFA uptake, exclusive of possible simultaneous FFA release, would appear necessary in studies concerned with human myocardial FFA metabolism.

Defective lipid metabolism in the failing heart

The metabolism of long chain fatty acids was investigated in the failing heart of guinea pigs with chronic constriction of the ascending aorta. Homogenates prepared form failing hearts exhibited (a) a decreased capacity to oxidize palmitic acid (failure = 0.50 +/- 0.06 mumole/g of protein per 20 min; control = 1.09 +/- 0.10); (b) a reduced level of carnitine, a myocardial constituent which serves to control the oxidation rate of long chain fatty acids in the heart (failure = 0.91 +/- 0.10 mumole/g wet weight; control = 1.69 +/- 0.10); and (c) an increased rate of palmitate incorporation into triglycerides and lecithin. Exogenous carnitine effected a restoration of the defective palmitate metabolism of the homogenates towards normal. In contrast to long chain fatty acid oxidation, glucose oxidation by the failing heart was not impaired. As a consequence of this selective lesion in energy substrate utilization, the failing heart might be forced to rely on substrates other than long chain fatty acids for its major energy supply.

Lipids of subcellular particles from bovine heart muscle. I. Fatty acids of neutral lipids

The fatty acid composition of various lipid classes obtained from subcellular fractions of bovine heart muscle by column chromatography on silicic acid has been examined by gas-liquid chromatography on diethyleneglycol succinate and Apiezon L columns. The nuclear and cytoplasmic fractions together constituted the major lipid compartments of the myocardial cell, the cytoplasmic subcellular organelles accounting for only about 4% of the total lipid. Among the total fatty acids of each subcellular fraction, there was a remarkable constancy in the relative amounts of monoethenoid fatty acids (about 23%). More than 90% of the total fatty acids had chain lengths between C18and C20. Approximately 3–4% of longer chain length fatty acids were present in the mitochondrial and cytoplasmic fractions. There was a predominance of monoenes (36%) and long chain fatty acids (> C20) in the cholesteryl esters associated with the "microsomal" preparation. Although the monoethenoid fatty acids of triglycerides were subject to considerable variation, the nuclear and cytoplasmic compartments consistently showed about 40% of this class of fatty acid. In sharp contrast to all other neutral lipid classes, polyethenoid fatty acids constituted a significant proportion of the total free fatty acids in all subcellular organelles. The heavy mitochondrial and cytoplasmic fractions showed relatively higher concentrations of polyethenoid free fatty acids. In view of the fact that free fatty acids constituted the main source of energy from fats for the myocardium, the hypothesis has been advanced that heart muscle mitochondria preferentially extract the readily oxidizable free polyunsaturated fatty acids from the cytoplasmic environment to fulfill the energy demands of the aerobic cell.

CONTROL OF REDUCED NICOTINAMIDE-ADENINE DINUCLEO-TIDE OXIDATION BY PIGEON-HEART MITOCHONDRIA

The rate of oxidation of 10–35 μM reduced nicotinamide–adenine dinucleotide (NADH) by pigeon-heart mitochondria was increased not only by osmotic swelling and sonic disruption of the organelles but also by milder procedures such as washing or dilution, which had no deleterious effect on the P: O and respiratory control ratios when glutamate was the substrate. In all cases, the enhanced oxidation of 10 μM NADH was suppressed by 5 mM adenosine triphosphate (ATP). From these and other findings it was concluded that the access of extra-mitochondrial NADH to the respiratory chain is controlled at a minimum of two sites. Control of NADH flux through the first site is lost after treatment of the mitochondria by procedures which increase their permeability. A second level of NADH control survives sonic disruption of the mitochondria and is a site at which the oxidation of 10 μM NADH is stimulated by Piand inhibited by ATP, adenosine diphosphate (ADP), and oxidized nicotinamide–adenine dinucleotide (NAD+). The ATP and ADP effects at this level are not blocked by oligomycin. Magnesium releases the adenine nucleotide inhibition of NADH oxidation under certain conditions, but its site and mode of action is not clear as yet. In these experiments, NADH oxidation was determined polarographically and photometrically at 28° in a medium containing 0.23 M mannitol, 0.07 M sucrose, 0.02 M Tris–chloride, and 0.02 mM ethylenediamine tetra-acetic acid (EDTA) at pH 7.2.