Analysis of rat heart in vivo by phosphorus nuclear magnetic resonance.

High-resolution 31P nuclear magnetic resonance spectra at 73.83 MHz are reported for rat heart in vivo. In live rats, it was possible to observe the cardiac content of ATP, phosphocreatine, and Pi. Only a small amount of whole-blood 2,3-diphosphoglycerate was observed in the spectra, precluding the possibility that blood phosphate compounds were masking the spectra of cardiac phosphate compounds. The 31P nuclear magnetic resonance spectra of in vivo and perfused rat hearts were similar and support the utilization of the perfused rat heart as a model system for studying high-energy phosphate metabolism of the heart in vivo. The dynamic flux of high-energy phosphate compounds was investigated by subjecting the rat to respiratory arrest. In this experiment, the heart followed the classic metabolic pattern known to occur during cardiac arrest; phosphocreatine and then ATP decreased in concentration while Pi increased in concentration. The 31P nuclear magnetic resonance analysis of rat heart in vivo is demonstrated to be a practical and feasible method for studying cardiac high-energy phosphate metabolism.