Myocardial ultrastructure in the isolated rabbit heart exposed to dopamine, dobutamine, isoprenaline, G-strofanthin, xamoterol and hypoxia.

The isolated spontaneously beating heart was used for comparing the effects of hypoxia and positive inotropic drugs on myocardial ultrastructure. Hypoxia gives a significant decrease in the volume fractions of mitochondrial cristae relative to the total mitochondrial volume (Vvmcristae) and a significant increase in the volume fraction of mitochondrial matrix relative to the total mitochondrial volume (Vvmmatrix), but changes in volume fractions of mitochondria (Vvmitochondria) and myofibrils (Vvmyofibrils) were absent. Significant changes in ultrastructure in hearts treated with dopamine (0.6 microM), dobutamine (90 nM), G-strofanthin (0.25 microM), xamoterol (32 nM) and isoprenaline (0.15 microM or 15 nM) were absent. Furthermore, myocardial effects in the isolated rabbit heart without exposure to any treatment showed a significantly decrease in oxygen consumption after 90 min. and a significant decrease in frequency of contractions after 120 min. perfusion time, but no change in contractility was seen. We conclude that this experimental model is useful in studies of positive inotropic drugs.