Rhythmic change of myocardial phosphate metabolite content in cardiac cycle observed by depth-selected and EKG-gated in vivo 31P-NMR spectroscopy in a whole animal.

The newly developed pulse width modulation method for the depth-selected in vivo NMR under high magnetic field (6.4 Tesla), sectional magnetic resonance (SMR), enabled us to selectively obtain and follow time sequence of P metabolism of rat heart in a whole body. An EKG-gated 31P-SMR spectroscopy at every 30 m sec, after the R wave, with calibrating the resonance intensity by an external standard, demonstrated a synchronous oscillation of both contents of creatine phosphate (CP) and beta-ATP: minimal at the early 2/3 of the systole as was identified by the aortic pressure measurement and maximal at the last 1/3 of the diastole, while inorganic phosphate content varied antiphasically to CP or ATP without obvious change of intracellular pH in cardiac cycle. This is the first report that described an in vivo detection of cyclic change of phosphate metabolites in the heart.