Regional differences in fatty acid oxidation by the adult rabbit myocardium

Differences in coronary perfusion and tissue oxygenation between the epicardium and endocardium have been shown. Thus, intrinsic capacity for substrate oxidation may also exhibit regional variation. Accordingly, homogenates of left ventricular papillary muscle ("endocardium") and left ventricular free wall trimmed of endocardium ("epicardium") were compared for their capacity to oxidize palmitic acid-1-14C (PA) and octanoic acid-1-14C (OcA). Homogenates from one to three rabbits were combined for each study; 18 studies were performed using PA, and 10 using OcA. The protein content of endo- and epicardial homogenates was the same (Biuret method). At ambient PA concentrations of 0.2 mM, oxidation of PA by "endocardium" was 64 +/- 6.3% that of the "epicardium" (p less than 0.001). At ambient concentrations of 1.0 mM, oxidation of OcA by "endocardium" was not different from that of "epicardium" (118 +/- 10.5%; p greater than 0.1). Thus, the oxidative capacity for long chain FFA by the endo- and epicardial homogenates are at variance. Differences in carnitine-mediated transmitochondrial transport of long chain fatty acids may be the explanation. Such regional metabolic differences could play a role in regional alterations in myocardial function under adverse hemodynamic and metabolic circumstances.