Metabolic and haemodynamic responses to adrenaline in normal dogs

The metabolic and haemodynamic effects of adrenaline were investigated in 6 intact anaesthetized dogs, which were subjected to an infusion of adrenaline. The dose given was similar to the endogenous production rate of adrenaline in experimental myocardial infarction. Adrenaline infusion (0.8, 1.17 ot 1.05 micrograms . kg-1 . min-1) over two hours led to a variable rise in blood level of this amine, regardless of the rate of infusion. Dogs with high blood adrenaline (over 3.5 ng . ml-1) exhibited haemodynamic deterioration, i.e. a rise in peripheral vascular resistance together with a fall in cardiac output and external cardiac work. Dogs with low blood adrenaline showed little change in peripheral vascular resistance, a rise in cardiac output and external cardiac work. The myocardial consumption of each of the substrates lactate, pyruvate, glucose and FFA was measured, and its equivalent oxygen consumption expressed as a percentage of the total myocardial oxygen consumption. No relationship was found between myocardial utilisation of individual substrates and the type of haemodynamic response. Thus in intact dogs exposed to adrenaline excess, similar to that found in acute myocardial infarction, the different types of haemodynamic response cannot be attributed to the type of substrate utilization by the myocardium, but to different rates of clearance of adrenaline. Low clearance rates lead to high blood adrenaline levels and an unfavourable response of the cardiovascular system.