• Six subjects with the phobic-anxiety syndrome were treated in a controlled, crossover trial of clonidine hydrochloride v imipramine hydrochloride for periods of four weeks each. During each drug trial and during baseline placebo treatment, each patient exposed himself or herself to a situation that previously elicited panic attacks. Self-rated anxiety and plasma levels of 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) were measured to study the effect of the drug treatments on noradrenergic activity and anxiety. Plasma MHPG level correlated highly with rated anxiety under all conditions, and was consistent with significant symptom reduction by clonidine or imipramine. Diminished suppression of plasma MHPG concentrations in two subjects was associated with the continued emergence of panic symptoms in response to phobic stimuli.
Ko GN, Elsworth JD, Roth RH, Rifkin BG, Leigh H, Redmond DE. Panic-Induced Elevation of Plasma MHPG Levels in Phobic-Anxious PatientsEffects of Clonidine and Imipramine. Arch Gen Psychiatry. 1983;40(4):425-430. doi:10.1001/archpsyc.1983.01790040079011