Carnitine palmitoyltransferase-I (
CPT-I) inhibitors improve postischemic myocardial function either by decreasing muscle long-chain acylcarnitines (LCAC) during
ischemia or by increasing oxidation of alternate substrates such as
glucose during reperfusion. These possibilities were evaluated using
oxfenicine, a
CPT-I inhibitor, and alternate substrates that bypass
carnitine-dependent metabolism. Isolated rat hearts subjected to 20 min of
ischemia followed by 40 min of reperfusion with 1.8 mM
palmitate as exogenous substrate recovered little function during reperfusion. Hearts made ischemic and reperfused with
palmitate and 2.4 mM
hexanoate as exogenous substrates had significantly improved reperfusion function compared to
palmitate-perfused hearts. Addition of 2 mM
oxfenicine to
palmitate-
hexanoate-perfused hearts gave an additional small improvement in reperfusion function. At the end of
ischemia, the LCAC content of hearts perfused with
palmitate or
hexanoate and
palmitate was identical.
Palmitate-,
hexanoate, and
oxfenicine-perfused hearts had significantly decreased LCAC content at the end of
ischemia compared with
hexanoate-
palmitate-perfused hearts. Therefore, depressed reperfusion function in long-chain
fatty acid-perfused hearts can be ameliorated by alternate substrates, including medium-chain
fatty acids. LCAC accumulation during
ischemia apparently plays only a minor role in the postischemic dysfunction of long-chain
fatty acid-perfused hearts.