Inhibition of contractility during the early phase of total ischaemia in the working heart. Recovery during reperfusion.

Total global ischaemia of the normothermic working rat heart caused an initial positive inotropic response characterized by vigorous contractions. After +/- 15 s this response reached a peak whereafter the isotonic contraction amplitude started to decline. After +/- 3.5 min the heart ceased to beat. The low level of high energy phosphates (HEP), determined 3 min after the onset of ischaemia, indicated that these phases of contractility during ischaemia might play a significant role in depleting HEP. This was substantiated by the observation that inhibition of the contractions during ischaemia by low calcium or high potassium solutions resulted in conservation of myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) stores. It also resulted in the prevention of contracture development during ischaemia and improved mechanical recovery during reperfusion. It was therefore concluded that inhibition of contractility immediately after the onset of total global ischaemia of the normothermic working rat heart is of prime importance in mechanical recovery during reperfusion.