Action of nimodipine on sympathomimetic mydriatics in humans

• Published in: Clinical neuropharmacology Vol. 15; no. 2; p. 120
• Main Authors: Alessandri, M, Pietrini, U, Bandini, E B, Beatrice, S, Fanciullacci, M
• Format: Journal Article
• Language: English
• Published: United States 01.04.1992
• Subjects: Administration, Oral; Administration, Topical; Adult; Drug Interactions; Female; Humans; Male; Nimodipine - pharmacology; Ophthalmic Solutions; Phenylephrine - pharmacology; Pupil - drug effects; Sympathomimetics - pharmacology; Tyramine - pharmacology
• ISSN: 0362-5664
• DOI: 10.1097/00002826-199204000-00006

In 12 healthy volunteers, the effects of a single oral dose of nimodipine (40 mg) on pupil size and on the mydriasis induced by conjunctival instillation of tyramine and phenylephrine were studied by using a TV monocular infrared pupillometer. Nimodipine alone was unable to modify the pupil area. When compared with placebo, the Ca2+ entry blocker reduced the pupil dilation caused by tyramine, whereas it did not affect the phenylephrine-induced mydriasis. Since tyramine provokes mydriasis by releasing neuronal norepinephrine, a full adrenoceptor agonist, whereas phenylephrine acts only on alpha 1-adrenoceptors insensitive of extracellular Ca2+, the hypothesis may be advanced that a heterogeneous population of alpha-adrenoceptors, located in the human iris dilator muscle and differently sensitive to Ca2+ entry blockade, is responsible for the reduction of the tyramine-induced mydriasis. Apart from this putative mechanism, the results suggest that nimodipine reduces the pupillary response to adrenergic activation in the human eye.