Alpha receptor blockade by thymoxamine in the human eye

Abstract

Thymoxamine blocks α‐adrenergic receptors in experimental animals. The instillation of 0.1 per cent thymoxamine into the human eye produces miosis which is maximal at 45 to 60 minutes and disappears after 1 to 2 hours. Pretreatment with thymoxamine eye drops prevents the production of mydriasis by phenylephrine 10 per cent or ephedrine 2 per cent. When mydriasis has been established by hydroxyamphetamine 1 per cent, thymoxamine reverses it, and miosis is apparent after 25 minutes. The importance of α‐adrenergic receptors in the mydriatic action of sympathomimetic amines is thus confirmed. This study illustrates the value of pupillary responses in studying the interaction of sympathomimetic amines with adrenergic neuron‐ and receptor‐blocking drugs in man.