Platelet alpha 2- and leucocyte beta 2-adrenoceptors in phaeochromocytoma: effect of tumour removal.

Platelet alpha 2- and leucocyte beta 2-adrenoceptors (as well as noradrenaline and adrenaline plasma levels) were studied in five patients with confirmed phaeochromocytoma using tritiated yohimbine and iodated cyanopindolol, respectively, before and after tumour removal. Patients with phaeochromocytoma had a lower leucocyte iodated cyanopindolol binding than control subjects, but no change in platelet tritiated yohimbine binding. Plasma catecholamine levels were higher than controls. Tumour removal induced a return to normal values of leucocyte iodated cyanopindolol binding and a decrease in plasma catecholamine levels. These results underline the potential interest of leucocyte beta-adrenoceptor quantification in the diagnosis and the follow-up of phaeochromocytoma. Pharmacologically, they show that down-regulation occurs in vivo for leucocyte beta 2-adrenoceptors but not for platelet alpha 2-adrenoceptors.