31P-NMR magnetization transfer study of reperfused rat heart.

The relationships between pressure rate product (PRP) and flux (PCr-->ATP) or flux(Pi-->ATP) were studied in isolated perfused rat hearts by the method of saturation transfer using 31P-NMR during the preischemic and reperfusion periods. The hearts were made ischemic for 15 min, followed by 60 min of reperfusion. PRP was almost completely depressed, and recovered to 60% of the control level (preischemic period) after reperfusion. The ATP level during reperfusion was significantly decreased, whereas there was no significant change in PCr level. Pi level of reperfused hearts was significantly higher than that in the control. Both flux(PCr-->ATP) and flux(Pi-->ATP) were significantly decreased during the reperfusion period (both p < 0.05). However, the flux(PCr-->ATP)/PRP ratio during reperfusion did not differ from that of the control. This result indicates that the decrease in flux(PCr-->ATP) was matched by a similar decrease in cardiac performance. In contrast, the flux(Pi-->ATP)/PRP ratio during reperfusion was significantly decreased compared to that of control. These results suggest that the stunned heart needs less ATP turnover in proportion to its depressed contractile activity, and flux(Pi-->ATP) may lmit the recovery of postischemic performance.