INVIVO PUPILLARY CONSTRICTOR EFFECTS OF SUBSTANCE-P IN MAN

The ocular effects of substance P (SP) were studied in 13 normal volunteers. Various concentrations of SP (0.135, 1.35 and 135-mu-g per 100-mu-l) were instilled into the conjunctival sac and pupillary area changes were evaluated by means of an electronic pupillometer. The ability of SP to modify the mydriasis induced by pretreatment with 1% homatropine eyedrops was also studied. The instillation of SP produced miosis in a dose-dependent manner without provoking any ocular disturbances. Furthermore, the highest concentration tested was unable to reduce the homatropine-induced mydriasis. These findings indicate that SP exerts a pupillokinetic action in humans which probably occurs via a receptor mechanism. Since muscarinic blockade is not overcome by the peptide instillation, the results do not clarify whether SP causes miosis acting on iris muscles and/or cholinergic fibres.