Platelet alpha 2-adrenergic receptor binding and plasma catecholamines. Before and during imipramine treatment in patients with panic anxiety.

Specific binding of tritiated clonidine, an alpha 2-adrenergic receptor agonist, and tritiated yohimbine, an alpha 2-adrenergic receptor antagonist, to platelet membranes was measured in persons with panic attacks or major depression and in normal subjects. Plasma catecholamine levels were measured in patients with panic attacks and in normal subjects. The number of binding sites in patients with panic attacks, as measured with tritiated clonidine, was lower than in depressed persons and was the same as in normal subjects. The number in patients with panic attacks, as measured with tritiated yohimbine, was lower than in either depressives or normal subjects. Catecholamine levels were somewhat higher in patients with panic attacks than in normal subjects. Treatment with imipramine hydrochloride decreased the number of sites, as measured with either ligand, in both patient groups and increased catecholamine levels in patients with panic attacks.