Altered functional activity and anoxic tolerance in diabetic rat isolated atria

Functional activities of isolated atria from 4-week diabetic rats and their anoxic tolerance and recovery were compared to those of control rats. The present study showed a two-fold increase in maximum developed contraction force (CF), the rate of force development, and the rate of relaxation in isolated atria from diabetic rat heart over that of the control. The rate of the sinoatrial node was lower in the diabetic. However, this lower rate was not responsible for higher CF of the diabetic isolated atria since the twofold difference was still present when both diabetic and control atria were electrically paced at identical rates. Although the high energy phosphate content of the diabetic isolated atria was lower than that of control (50% lower phosphocreatine and 15% lower ATP), diabetic atria exhibited improved short term anoxic tolerance and recovery compared to that of the control. The recovery from long term anoxia, however, was better in control than in diabetic atria, considering the higher original CF in diabetic atria. The present observations are compatible with better ischemic tolerance and higher basal force development observed by some investigators on diabetic isolated heart preparations but not with impaired contractility reported by others. Possible mechanisms responsible for the observed changes are discussed.