Effects of regional ischemia on metabolic function in adjacent aerobic myocardium

Increased mechanical demands are placed on aerobic heart muscle during restrictions in coronary flow to myocardium adjacent to and contiguous with normally perfused tissue. In a preparation of regional ischemia (ten intact working swine hearts), changes in substrate preference and utilization were detailed in separate beds of perfused myocardium before and during regional disruptions in coronary flow. Mild-to-moderate levels of ischemia (?52Δ% reduction in flow to the anterior left heart) caused significant declines in both regional and global estimates of mechanical function (?39 and ?31Δ% in regional and global work indices, P < 0.05 and P < 0.025, respectively). Oxygen consumption and fatty acid oxidation were reduced in ischemic muscle. Conversely, in normally perfused myocardium and presumably in response to increased mechanical burdens, oxygen consumption and fatty acid uptake were increased (+29 and +80Δ%, respectively). There was no commensurate increase in ¹⁴CO₂ production from labeled palmitate, however, and certain fatty acid intermediates (long chain acyl CoA and carnitine) appeared increased. To compensate metabolically, a greater preference for glucose utilization (two-fold increase in uptake) was documented in non-ischemic myocardium and energy production was maintained. Thus, although glucose has long been argued to treat acute and chronically ischemic myocytes (with mixed results), an alternate source of benefit may derive from its effects on preserving cell viability and function in adjacent aerobic heart muscle.