Quantitative study on the relation between structural and functional properties of the hearts from three different mammals.

The ultrastructural quantitative composition of left ventricular cardiac myocytes from isolated Langendorff-perfused hearts was studied in three different mammals (rabbit, guinea pig, and rat). Volume densities of mitochondria, myofibrils, and unspecified cytoplasm were determined using morphometry and were compared to functional parameters including left ventricular developed pressure (LVDP), contractility (dP/dt), heart rate, TTI (tension-time index, an index of oxygen consumption), and relative heart mass (H/B) obtained from these hearts. Each of the mammals was found to possess a very specific and characteristic quantitative composition of cardiac myocyte. Cardiac myocytes contained 26.8% mitochondria and 56.3% myofibrils in rabbits, 25.8% mitochondria and 60.9% myofibrils in guinea pigs, and 27.7% mitochondria and 58.1% myofibrils in rats. The LVDP, contractility, heart rate, and TTI were quite different among species. However, there were close correlations between the mitochondrial volume density and the LVDP (p < 0.05), and between the mitochondrial volume density and the TTI (p < 0.05), in any group of the animals. It is concluded that the mitochondrial volume density is a good indirect indicator of function of cardiac muscle related to oxidative capacity.