Pupil Studies in Depressed Patients: An Investigation of the Mechanism of Action of Desipramine

Six depressed patients were treated routinely with desipramine, a relatively selective noradrenergic uptake blocking drug. After 0, 1 and 3 weeks' treatment, pupillary responses to tyramine, phenylephrine and pilocarpine were measured using a photographic techniques. Both 1 and 3 weeks' treatment significantly inhibited tyramine and phenylephrine-induced mydriasis, but did not inhibit pilocarpine-induced miosis; in fact the longer treatment enhanced miosis due to pilocarpine. Resting pupil size was significantly increased after 1 and 3 weeks' treatment. The findings can be explained by the known ability of desipramine to block noradrenaline uptake and alpha adrenoceptors: they provide no evidence of muscarinic receptor blockade or of a slowly developing adaptation at alpha adrenoceptors.