P. Cuchet

Is oxygen supply sufficient to induce normoxic conditions in isolated rat heart

SummaryThe aim of this study is to assess whether oxygen supply is sufficient to induce normoxic conditions in isolated rat hearts. Hearts are perfused with a Krebs medium supplemented with 11mM glucose, 0.6 mM lactate, 0.06 mM pyruvate, non delipidated albumin (0.1 mM fatty acids), and either 1.78 mM or 0.76 mM free calcium, at 10ml.min−1. Graded hypoxia is induced by a stepwise decrease of partial pressure of oxygen (PO2) from 660 to 52 mmHg. Contractile performance, oxygen uptake and lactate plus pyruvate balance are assessed. With high calcium, left ventricular developed pressure, dP/dt max and oxygen uptake increase linearly with PO2 up to 660 mmHg; heart rate increases with PO2 up to 250 mmHg and then tends to stabilize. With low calcium, all parameters reach a plateau over 400 mmHg. Lactate plus pyruvate production suggests a stimulation of glycolysis with high calcium, even at 660 mmHg; conversely, there is no lactate plus pyruvate production with low calcium over 250 mmHg. In conclusion, our results demonstrate that, under a high level of calcium at a constant flow of 10 ml.min−1, cardiac function is always limited by O2 supply, except for heart rate. This raises the question as to the definition of a normoxic state. The better preservation of heart rate during hypoxia, compared to other dynamic parameters, could be explained by a contribution of glycolytic ATP.

The intramyocardial fate of [1-14C] palmitate, iodopalmitate and iodophenylpentadecanoate in isolated rat hearts. A contribution to the choice of an iodinated fatty acid as a tracer of myocardial metabolism

Labeled iodinated fatty acids (FAs) have been proposed to explore myocardial metabolism by external detection in man. We have chosen a 16-carbon FA, iodinated in omega position, whereas other authors use an iodophenylated FA. To explore the influence of the presence of an iodine or of an iodophenyl radical on the metabolism of the FA, we have compared, in isolated rat hearts perfused in a recirculating system, the intramyocardial fate of palmitate (PA), iodopalmitate (IPA), and iodophenylpentadecanoate (IPPA), the 3 of them being labeled with C14 in position 1. The addition of the iodine atom brings about a hindrance to the esterification of the FA into triglycerides, but not modification of the myocardial uptake and of the CO2 produced. The addition of the iodophenyl radical impairs both the FA storage and its oxidation, leading to a very high level of free FA. The phospholipid distribution is also modified. Apart from their myocardial use in the isolated rat heart, the 3 FAs were assayed in vitro as a substrate for acylCoA-synthase. As IPA more closely mimics native FA metabolism, it is therefore more suitable than IPPA as a tracer of myocardial metabolism.

Intramyocardial fate of 15-p-iodophenyl-?-methylpentadecanoic acid (IMPPA): Is it a good tracer of fatty acid myocardial uptake?

Iodinated fatty acids (FAs) are now used in Nuclear Medicine to assess, by external detection, myocardial metabolism. Methylated FAs have been proposed as tracers of FA myocardial uptake. IMPPA is a new FA analogue in which a methyl group have been introduced in β position to inhibit β-oxidation and a terminal phenyl group prevents a possible omega oxidation. We have compared the intramyocardial behaviour of this FA with the 15-p-iodophenyl-pentadecanoic acid (IPPA), the straight chain analogue, and with the 15-phenyl-β-methylpentadecanoic acid (MPPA), the 3 of them being labelled with C14 on the carboxyl group, in isolated rat hearts perfused in a recirculating system.

An experimental model of hypoxia on isolated rat heart, in a recirculating system: Study of fatty acid metabolism with an iodinated fatty acid

An experimental model of hypoxia was developed on isolated rat heart to study the effects of hypoxia on cardiac performance and metabolism. Fatty acid (FA) metabolism was explored by external detection with a labelled FA, iodohexadecenoic acid (IHA). Hearts, after 30 min preperfusion in an open system, were transferred in a recirculating system for 40 min and perfused with oleate, glucose, lactate, pyruvate and IHA, either in normoxia (pO2 = 660 mmHg) or in hypoxia (pO2 = 220 mmHg). After 40 min hypoxic recirculation, oxygen uptake and dynamic parameters, except the heart rate, decreased respectively by 56% and 44%, and remained constant throughout the perfusion. Glucose utilization increased 2 fold, endogenous glycogen fell by 50% and lactate + pyruvate production increased 3 fold, showing a stimulation of glycolysis. Oleate uptake decreased by 28%, while triglycerides content remained higher. The ATP/ADP ratio decreased by 24%. Conversely to oleate, IHA uptake was not significantly modified, but its intracellular fate showed a higher radioactivity in all lipid fractions: polar lipids, diglycerides, free FAs and triglycerides. beta oxidation of IHA, evidenced by iodide production, decreased by 39%. The external detection of cardiac radioactivity allowed us to obtain time-activity curves that were analyzed with a 4-compartment mathematical model. The data evidenced an esterification ratio significantly higher in hypoxia. The metabolism of IHA as estimated by the intracellular analysis or, in a non-invasive way, by external detection, was similar to the metabolism of oleate. Thus, lipid metabolism, in hypoxia, can be explored by external detection with IHA.

Assessment of iodohexadecenoic acid as a tracer of fatty acid metabolism by external detection: a study on isolated rat heart

Labelled fatty acids have been proposed to explore cardiac metabolism. For the analysis of the external detection curve obtained with 16-iodo 9-hexadecenoic acid (IHA), we developed a mathematical 4-compartment model with compartments 0, 1, 2 and 3 representing vascular IHA, intracellular IHA, esterified forms and iodide, respectively. This model, used here for isolated rat hearts perfused in a recirculating system, is validated by an intracellular analysis, then tested in various metabolic conditions. Thus, the mathematical analysis of the external detection curve gives us numerical data on IHA metabolism, especially the distribution between degradation and storage. Our results confirm the suitability of IHA for assessing myocardial metabolism.