Absolute and relative myocardial ischemia by isoproterenol overdosage

Administration of greater than or equal to 10 mg/kg isoproterenol in rats absolutely diminished local myocardial blood flow within 0.5 min continuing up to 45 min. The blood flow reduction was followed by an increased lactate content and a decrease of both the intracellular redox potential and the content of high energy phosphates in the myocardium. The graduation of the initial lactate accumulation in different myocardial regions corresponds to the myocardial distribution of the infarct-like necroses occurring 24 h later. The very early alterations are comparable with an absolute (blood flow reduction), irreversible, and acute ischemia. In the dose range from 0.05 to 1 mg/kg of isoproterenol, an acceleration of the local myocardial blood flow was caused which, however, was accompanied by ischemia-like disturbances, too. Therefore, this condition is considered as a relative ischemia, an increased but insufficient blood supply.