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Using individually estimated clearance rates, renal insufficiency no longer hampers calculation of infarct size from FABP and MYO, and reliable estimates of total myocardial damage can be obtained within 24 h after first symptoms.

Considering the excellent precision data and the result equivalence for most assays, it can be concluded that Cobas 6,000 accommodates robust chemistry and immunochemistry, and has good potential for workstation consolidation in medium-sized laboratories.

To investigate the effect of lactate, pyruvate, and glucose on the endogenous levels of lipids in the normoxic, ischemic, and reperfused myocardium, isolated working rat hearts were exposed to various grades of ischemic insult (15, 30, or 45 minutes). Glucose was present as the basal substrate in the perfusion medium, and lactate (5 mM) or pyruvate (5 mM) was added as the cosubstrate. Lipid metabolism was evaluated by fatty acid accumulation, triacylglycerol turnover, and phospholipid homeostasis. Exogenous lactate significantly increased fatty acid content above preischemic levels after 45 minutes of ischemia. In glucose-perfused hearts, fatty acid levels were even slightly higher than in lactate-perfused hearts, whereas pyruvate-perfused hearts demonstrated less accumulation of fatty acids. By reperfusion, fatty acid levels in glucose-perfused hearts returned to control values. In lactate- and pyruvate-perfused hearts, fatty acid accumulation was further enhanced by reperfusion. When the fatty acid content exceeded 400 nmol/g dry wt during reperfusion, hemodynamic function was impaired, whereas fatty acid levels below 400 nmol/g dry wt did not correlate with hemodynamic recovery. The total triacylglycerol content did not change during ischemia and reperfusion. However, accumulation of glycerol was remarkable during the first 15 minutes of ischemia in all hearts, and release of glycerol by reperfusion was considerable in lactate-perfused hearts after 30 minutes of ischemia and in all groups of hearts after 45 minutes of ischemia. Release of glycerol in association with maintained levels of triacylglycerols suggests turnover of the triacylglycerol pool. The rate of triacylglycerol cycling correlated poorly with hemodynamic recovery. Accumulation of arachidonic acid revealed disturbances in phospholipid turnover. Arachidonic acid accumulation during reperfusion demonstrated a strong relation with impairment of cardiac function. Hence, derangements in phospholipid homeostasis during reperfusion might be involved in myocardial damage, which is influenced by the substrates available.

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Glycerol release has been generally accepted as an index of lipolysis in the intact heart. The glycerol moiety of glycerol-3-phosphate (glycerol-3-P) is incorporated into triacylglycerols, which are then hydrolysed with release of glycerol. This study investigates the possibility that glycerol may be derived directly from glycerol-3-P instead of passing through the triacylglycerol pool. The cardiac capacity for hydrolysis of glycerol-3-P into glycerol was determined in homogenates of rat hearts. Glycerol-3-P hydrolysis activity in homogenates increased with decreasing pH. The activity was approximately four times higher at pH 5.0 than at pH 7.2 (0.94 +/- 0.11 and 0.25 +/- 0.03 mumol.g wet weight-1.min-1 respectively). The substrate concentration at which half-maximal glycerol-3-P hydrolysis activity was reached did not significantly differ at pH 5.0 and pH 7.2 (4.2 +/- 1.1 mM and 2.9 +/- 1.0 mM respectively). In the intact heart, the pH and substrate conditions found under ischaemia are favourable for direct conversion of glycerol-3-P into glycerol. The glycerol-3-P hydrolysis activity measured in vitro was sufficiently high to account for glycerol production in the ischaemia heart. However, the lack of a stoichiometric relation between cardiac glycerol-3-P and glycerol levels in ischaemia indicates that production of glycerol cannot be explained solely by hydrolysis.

Complete cessation of flow in isolated rat hearts for 90 min resulted in a gradual breakdown of ATP and concomitant accumulation of degradation products, such as adenosine, inosine (major break-down product), hypoxanthine, and, to a lesser extent, xanthine. After 45 min of ischemia, the content and relative composition of purines hardly changed, whereas the AMP content continued to rise. This finding points to constraints on AMP degradation and flux through the degradation pathway from adenosine to uric acid in the ischemic heart. In myocardial preparations, the cells of which were deliberately disrupted by freezing and thawing before anoxic incubation, AMP did not accumulate and was finally converted to hypoxanthine. These results indicate that compartmentalization of substrates and enzymes is responsible for the observed preferential accumulation of AMP and inosine in the ischemic heart. Inhibition of hypoxanthine degradation is explained by the absence of oxygen. Restoration of flow and oxygen supply abolished the inhibition of metabolic flux. Accumulated purines were released into the coronary effluent and, concomitantly, further metabolized. Comparison of tissue levels of hypoxanthine, xanthine, and uric acid before reperfusion and the amounts released during reperfusion indicates that in rat myocardium substantial amounts of potentially hazardous xanthine oxidase-derived reactive oxygen species are likely to be formed during the early reperfusion phase.