Measurement of myocardial fatty acid esterification using [1-¹¹C]palmitate and PET: comparison with direct measurements of myocardial triglyceride synthesis

The purpose of the present study was to assess the accuracy of rates of myocardial fatty acid esterification (MFAE) obtained using positron emission tomography (PET).

Sixteen dogs were studied after an overnight fast (FAST), during a euglycemic hyperinsulinemic clamp (CLAMP), or during infusion of intralipid (IL) or IL plus dobutamine (IL/DOB). MFAE was quantified using [1-¹¹C]palmitate and PET and compared to the rate of triglyceride (TG) synthesis measured using [1-¹³C]palmitate and tissue sampling. Plasma free fatty acid (FFA) concentration varied ~20-fold across groups, with this variation in FFA availability accompanied by a ~20-fold range in TG synthesis. MFAE varied ~12-fold across groups, and was significantly correlated with TG synthesis (R = 0.80, P < .001). MFAE, however, was 3- to 4-fold higher than TG synthesis in FAST, CLAMP, and IL, but only ~50% higher when cardiac work was increased in IL/DOB, suggesting that MFAE reflects, in part, the incorporation of label into amino acids via TCA cycle exchange reactions.

Changes in MFAE parallel changes in TG synthesis, at least in the basal state. Although the data need to be interpreted cautiously, such measurements should be useful for quantifying acute changes in FFA storage by the heart in various pathophysiological states.