Isovolemic hemodilution: correlations of mitochondrial and myocardial performance.

: Subsarcolemmal (SS) and interfibrillar (IF) cardiac mitochondrial respiratory activities were examined under conditions of isovolemic hemodilution in rats. Experimental animals (mean Hct, 21%) had significantly higher cardiac indices than controls (mean Hct, 41.5%) 18 hours following isovolemic hemodilution with 0.9% NaCl. A 40% increase in cardiac output was associated with a significant increase in the respiratory control index (RCI) of the IF mitochondria. This increase in IF RCI occurred as a result of a significant decline in the ADP-independent (State 4) respiratory rate. These data demonstrate the ability of cardiac mitochondria to respond to increased myocardial demand by increasing mitochondrial efficiency and support the concept of subspecialized populations of mitochondria within the myocardial cell.