Myocardial metabolism and performance during sodium salicylate infusion in dogs

Quantitative assessment of anaplerosis from propionate in pig heart in vivo

Normal cardiac metabolism requires continuous replenishment (anaplerosis) of catalytic intermediates of the citric acid cycle. Little is known about the quantitative aspects of propionate as a substrate of in vivo anaplerosis; therefore, we measured the rate of propionate entry into the citric acid cycle in hearts of anesthetized pigs. [U-(13)C(3)]propionate (0.25 mM) was infused in a coronary artery branch for 1 h via an extracorporeal perfusion circuit, and cardiac biopsies were analyzed for the mass isotopomer distribution of citric acid cycle intermediates. Infusion of propionate did not affect myocardial oxygen consumption, heart rate, or contractile function. In the infused territory, propionate infusion did not affect uptake of glucose and lactate but decreased free fatty acid uptake by one-half (P < 0.05). Propionate extraction and uptake were 57.4 +/- 3.3% and 0.078 +/- 0.009 micromol x min(-1) x g(-1). Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 +/- 1.3% of the citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 +/- 0.002% of propionate uptake. Methylcitrate did not accumulate. Thus administration of a low concentration of propionate appears to be a convenient and safe way to boost anaplerosis in the heart.

Cardioprotection by anti-ischaemic and cytoprotective drugs

Cardioprotective drugs are agents that prevent or moderate harmful consequences of impaired cardiac energetics, such as sudden coronary death (SCD) due to early post-occlusion ventricular fibrillation (EPVF), development of incapacitating myocardial necrosis. Cardioprotection may be due to anti-ischaemic action, correcting the imbalance between vascular supply and myocardial demand for blood, but also to cytoprotective effect, preserving cellular integrity in the presence of factors damaging structure and function of the cardiac cell membrane such as ischaemia, ionic imbalance and that of pH, etc. Neither anti-ischaemic nor cytoprotective effect alone, or in combination, are sufficient to warrant full cardioprotection, i.e. both prevention of SCD and limitation of infarct size. Thus the beta-blocker pindolol which is anti-ischaemic in its effect reducing myocardial O2 demand and protects from SCD and EVFP, failed to limit infarct size. Even interventions of a mainly cytoprotective type of action protecting from SCD and EPVF, such as the linoleic acid-rich diet, or lidocaine, were unable to limit infarct size, 7-oxoPGI2 (anti-ischaemic and cytoprotective) failed to protect from SCD, VF and did not limit infarct size. On the other hand the nonsteroidal anti-inflammatory drugs which, like salicylates or sulfinpyrazon, reduce myocardial O2 demand and protect from post-occlusion SCD and EPVF, effectively limiting infarct size.

Effects of a selective thromboxane synthetase inhibitor, dazoxiben, and of acetylsalicylic acid on myocardial ischemia in patients with coronary artery disease

Thromboxane A2 (TxA2) may aggravate myocardial ischemia by inducing vasoconstriction and platelet aggregation in small coronary vessels, whereas prostacyclin (PGI2) counteracts these effects. Acetylsalicylic acid (ASA) inhibits the formation of TxA2 as well as PGI2, whereas dazoxiben, a thromboxane synthetase inhibitor, reduces TxA2 formation selectively. In 25 patients with coronary artery disease, 2 identical atrial pacing stress tests were performed: before and after the administration of dazoxiben (200 mg) in 15 patients and before and after ASA (250 mg) in 10. The ischemic response, quantified by coronary sinus and aortic lactate levels and by ST depression, was significantly reduced after administration of dazoxiben (p less than 0.02) but not after ASA. Heart rate at rest, myocardial extraction of free fatty acids and the arteriovenous oxygen difference was unaffected by medication. Both drugs reduced TxB2 levels to the same extent, whereas collagen-induced aggregation was more reduced after ASA than after dazoxiben. The effect of dazoxiben on ischemia was probably a result of inhibited TxA2 and preserved PGI2 production, which increased blood flow to ischemic regions.

Influence of free fatty acids on myocardial oxygen consumption and ischemic injury

Myocardial oxygen consumption (MVO2) is influenced by the substrate supply to the heart. Utilization of free fatty acids increases MVO2, and catecholamines sensitize the heart to the oxygen-wasting effect of free fatty acids. Alteration of myocardial metabolism from mainly free fatty acid to carbohydrate oxidation reduces the extent of myocardial ischemic injury. Within the ischemic myocardium, lipolysis is stimulated with breakdown of endogenous triglycerides to fatty free acids and glycerol. Antilipolytic agents seem to have a combined effect on myocardial metabolism partly through inhibition of lipolysis in adipose tissue with reduction of free fatty acid mobilization to plasma, and partly through a local inhibition of lipolysis in the ischemic myocardium. In patients with high sympathoadrenal activity, for example, patients with acute myocardial ischemia in unstable ischemic heart disease, elevation of free fatty acids might effect a critical increase in both myocardial oxygen requirement and infarct size.

Effect of myocardial ischaemia and antilipolytic agents on lipolysis and fatty acid metabolism in the in situ dog heart

Myocardial metabolism was studied in open-chest dogs before and during induction of myocardial ischaemia by coronary artery occlusion. Blood was sampled from a local coronary vein draining ischaemic tissue and from coronary sinus draining predominantly nonischaemic tissue. In the basal state, induction of myocardial ischaemia stimulated myocardial lipolysis as shown by release of glycerol from the ischaemic zone. During isoprenaline infusion, free fatty acids (FFA) extraction across the ischaemic myocardium was substantially increased, but no glycerol release occurred. Pretreatment with nicotinic acid or sodium salicylate markedly depressed FFA extraction across ischaemic myocardium, both during basal and isoprenaline stimulated lipolysis and nicotinic acid most likely inhibited lipolysis in the ischaemic zone. Thus, reduced severity of acute ischaemic injury by antilipolytic treatment might be due to a combination of inhibited myocardial lipolysis and reduced FFA extraction.

Applications and limitations of measurement of 15-keto,13,14-dihydro prostaglandin E2 in human blood by radioimmunoassay

It has been anticipated that the inherent limitations of radioimmunoassays for prostaglandin E (PGE) would be obviated by assays for its major circulating metabolite, 15-keto, 13,14-dihydro PGE2) which has a longer half-life in blood. We examined the effects of PGE2 infusion and alterations in lipolysis in vivo, and of clotting, prolonged storage and hemolysis in vitro, on KH2-PGE2 immunoreactivity in unextracted human plasma and serum samples. Indeed KH2-PGE2 levels rose several hundred fold during infusions of PGE2 at doses which cause little or no increment in peripheral PGE levels. During stimulation of lipolysis by infusions of epinephrine, apparent KH2-PGE2 levels rose five-fold. However, the dilution curve of plasma obtained during stimulation of lipolysis was not parallel to the standard curve; furthermore, apparent KH2-PGE2 levels were correlated strongly with free fatty acid (FFA) levels, suggesting that FFA's cross-reacted in the RIA weakly but significantly due to their very high molar concentration in blood. Clotting and prolonged storage of samples, but not hemolysis, also caused marked apparent increments in KH2-PGE2 levels. Competition curves using dilutions of such samples were again not parallel to the standard curves in plasma or buffer, but resembled dilution curves of samples containing high levels of FFA. These results suggest that handling of human blood samples for KH2-PGE2 measurement must be carefully standardized to avoid significant artifacts which presumably are due in part to fatty acids released from triglyceride stores in vivo or from disrupted membrane phospholipids in vitro. Unextracted plasma appears to be unsatisfactory for use in this RIA.

Cardiac effects of thoracic epidural analgesia before and during acute coronary artery occlusion in open-chest dogs

The effects of thoracic epidural analgesia (TEA) on myocardial performance and metabolism and on the severity of an acute myocardial ischaemia, were studied in eight anesthetized open-chest dogs. TEA reduced mean arterial blood pressure (AP) by 26%, heart rate (HR) by 20%, left ventricular dP/dt by 37%, and myocardial oxygen consumption by 27%. Although arterial concentrations of free fatty acids, glucose and lactate were unchanged, their myocardial uptake was reduced in proportion to the reduction in mechanical activity of the heart. Acute ischaemic injury was estimated from epicardial ECG recordings 10 min after occlusion of a branch of the left anterior descending coronary artery. In seven of eight dogs TEA caused a substantial reduction in the severity of the acute myocardial ischaemic injury. In the eight dogs investigated, the sum of ST segment elevations in epicardial ECG recordings was reduced from 34.0 +/- 3.4 to 23.3 +/- 2.8 mV (mean +/- SEM, P less than 0.01). After restoration of AP and HR to control values with phenylephrine and atrial pacing, the favourable effect of TEA on myocardial ischaemic injury was abolished. It is concluded that TEA effected a reduction in the severity of myocardial ischaemia in open-chest dogs, mainly through reduction of myocardial mechanical activity with consequent reduction of myocardial metabolism.

Effects of sodium salicylate on plasma insulin concentration and fatty acid turnover in dogs

The effects of intravenous sodium salicylate administration on plasma concentrations of insulin, free fatty acids (FFA) and glucose were studied in intact, anaesthetized dogs both during basal and isoprenaline stimulated lipolysis. In both situations sodium salicylate reduced the plasma concentrations of insulin. The reduction was associated with decreased plasma FFA concentrations and FFA turnover rate, while plasma glucose concentrations remained unaltered. The reduced plasma insulin concentrations effected by sodium salicylate is most likely secondary to the concomitant fall in plasma FFA concentrations due to inhibition of FFA mobilization from adipose tissue.

Distribution of coronary blood flow during acute coronary occlusion in dogs. Effect of nicotinic acid and sodium salicylate

The effects of the antilipolytic agents nicotinic acid (NA) and sodium salicylate (SS) on the distribution of coronary blood flow during acute myocardial ischaemia were studied in open chest dogs. Fifteen min following experimental coronary artery occlusion, blood flow in the ischaemic myocardium was on average 28% of flow in the non-ischaemic myocardium. The reduction in blood flow in the ischaemic mycardium was more pronounced in the endocardial than in epicardial halves of the myocardium. No significant change in blood flow was observed after administration of NA or SS in either the ischemic or nonischemic part of the myocardium. Both drugs reduced the extent of myocardial ischaemic injury as shown by reduced epicardial ST-segment elevations. Arterial concentrations of fatty acids were lowered by NA or SS, whereas the mechanical activity of the heart remained unchanged. It is concluded that the reduction of acute myocardial ischaemic injury effected by NA or SS is not due to changes in myocardial blood flow, but more likely to lower myocardial oxygen demand related to reduced fatty acid utilization.

Effects of acute myocardial ischaemia on platelet aggregation in the coronary sinus and aorta in dogs

The effect of an acute myocardial ischaemia on circulating platelet aggregates (CPA) in the coronary sinus and aorta was studied in open chest dogs. Even before induction of myocardial ischaemia significantly more CPA were found in the coronary sinus than in the aorta. Acute myocardial ischaemia produced by a non-thrombotic coronary artery occlusion increased CPA in coronary sinus, but not in aorta. Administration of acetylsalicylic acid (ASA) reduced the extent of the myocardial ischaemia as evidenced by reduced ST-segment elevations in epicardial ECG. Before induction of myocardial ischaemia, ASA significantly reduced CPA in coronary sinus, but no significant effect was observed during myocardial ischaemia. In the aorta no effect of ASA on CPA was found.

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.