Time course of alpha 2-adrenoceptor desensitization induced by adrenaline infusion in man.

After a rapid increase in infusion rate of adrenaline to elevate the initial heart rate by more than 15%, a continuous infusion was sustained in order to maintain elevated adrenaline plasma levels. At the end of the first phase of the experiment, the thrombocyte alpha 2-adrenoceptor number (determined by radioligand binding) was significantly lowered. After the second part of the experiment, a further significant decrease in the density of binding sites was observed, while elevated adrenaline plasma levels were kept constant. The decrease in the number of binding sites was accompanied by a slight increase in affinity of the radioligand. Serum potassium concentration significantly decreased during the experiment, while other serum electrolytes showed no significant alterations.