Post-anoxic recovery of myocardial performance in senescent mice

Abstract

In studies with intact open-chested male mice, the ability of the myocardium to maintain left ventricular pressure (LVP) during and subsequent to 3 min of anaerobic respiration has been studied. The hearts of young (6 months) and old (24 months) animals revealed dissimilar pressure profiles throughout the anoxic and recovery periods. Uppon re-establishment of aerobic respiration, only old animals were able to restore LVP to pre-anoxic levels. Indices of external myocardial work were similar in young and old hearts prior to anoxia and declined significantly more in young animals during anoxia and recovery. In order to localize the energy source for the recovery of myocardial performance by old animals myocardial and hepatic levels of glycogen and phosphorylase were assessed. Cardiac glycogen and phosphorylase levels were similar in both young and old animals prior to the recovery period. Upon recovery from anoxia, old animals were able to restore myocardial glycogen content and phosphorylase activity towards pre-anoxic levels while the hearts of young animals failed to do so. Pre-anoxic hepatic glycogen content in old animals was significantly greater than young animals while phosphorylase levels were similar in both groups prior to anaerobic respiration. Hepatic glycogen utilization and phosphorylase activation throughout the respiratory period were similar to that seen in the myocardium from both young and old animals with old animals displaying a greater utilization of glycogen and a greater activation of phosphorylase during anoxia and a greater tendency to return to pre-anoxic levels during the recovery period. In addition, blood glucose levels during anoxia were significantly lower in young animals when compared to values obtained from old animals. Under these conditions, increases in liver glycogen may be responsible for the maintenance of myocardial performance during and after anoxia by old mice.