Action of nimodipine on sympathomimetic mydriatics in humans.
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.
Alessandri
M
M
Institute of Internal Medicine and Therapeutics IV, Headache Centre, Florence University, Italy.
Pietrini
U
U
Bandini
E B
EB
Beatrice
S
S
Fanciullacci
M
M
D000284:Administration, Oral; D000287:Administration, Topical; D000328:Adult; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008297:Male; D009553:Nimodipine / Q000494:pharmacology*; D009883:Ophthalmic Solutions; D010656:Phenylephrine / Q000494:pharmacology; D011680:Pupil / Q000187:drug effects*; D013566:Sympathomimetics / Q000494:pharmacology*; D014439:Tyramine / Q000494:pharmacology
D009883:Ophthalmic Solutions; D013566:Sympathomimetics; D010656:Phenylephrine; D009553:Nimodipine; D014439:Tyramine