Metabolic and physical changes during calcium paradox induced in the rat heart.

Early changes in metabolic and physical properties were determined in rat hearts during calcium paradox. Calcium paradox was induced under constant perfusion pressure (60 mmHg) or constant coronary flow rate (9.8 ml/min). Within 30 s after calcium repletion, in either case, NADH increased, despite a decrease in ATP and increases in ADP and AMP. Surface spectrophotometry showed a deoxygenation of the myoglobin, thereby indicating myocardial oxygen depletion. These changes were predominant under conditions of constant pressure perfusion. In association with a rapid development of contracture, there were also a reduction in coronary flow (18%) in constant pressure perfusion, and an increase in perfusion pressure (208%) under constant flow perfusion. Thus, tissue deoxygenation has to be given due attention in the early development of calcium paradox, particularly in case of a constant pressure perfusion. Under constant flow perfusion, the physical stress due to high pressure perfusion against contracture may play an important role in the development of calcium paradox. This may be the first reported evidence for tissue anoxia in calcium paradox.