In normal dogs, when arterial lactate concentration was raised above 4.5 mmol/L, 87% of the total substrate oxidized by the myocardium was lactate, even in the presence of high glucose or FFA.
Does the normal dog heart preferentially utilize lactate over glucose or free fatty acids when arterial lactate levels are elevated?
In normal dogs, the myocardium preferentially utilizes lactate for energy production over glucose or free fatty acids when arterial lactate levels are elevated.
This study was undertaken to investigate whether the normal dog heart would switch to lactate as the preferred substrate when the arterial lactate level was raised. Sodium L-Lactate (pH adjusted to 7.0) was infused intravenously in sufficient quantity to raise the arterial lactate levels to those found in moderate to severe exercise (over 4.5 mmol . litre-1). The dogs were studied under chloralose anaesthesia breathing spontaneously. Blood samples were obtained from a branch of the femoral artery and the coronary sinus, and analysed for lactate, glucose, fatty free acids (FFA) and oxygen content. The ratio of lactate consumption to oxygen consumption was used to express the amount of lactate oxidised as a percentage of total substrate. This ratio was found to be a function of arterial lactate and reached a maximum at an arterial lactate concentration of 4.5 mmol . litre-1; this was uninfluenced by raised arterial glucose or FFA--the myocardium preferred lactate to glucose or FFA. A direct measurement of lactate oxidised as a percentage of total fuel was obtained in experiments with L-Lactate-14C(U), these showed that when the arterial lactate concentration was above 4.5 mmol . litre-1, even in the presence of high glucose or FFA, 87% of the total substrate oxidised was lactate. These results show that when the normal dog heart is presented with a choice of substrates, lactate is the preferred substrate for energy production.
Drake et al. (Fri,) conducted a other in Normal myocardium. Intravenous Sodium L-Lactate infusion was evaluated on Lactate oxidised as a percentage of total substrate. In normal dogs, when arterial lactate concentration was raised above 4.5 mmol/L, 87% of the total substrate oxidized by the myocardium was lactate, even in the presence of high glucose or FFA.
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