Abstract
It has been shown that pilocarpine dilates the normal and constricts the denervated pupil of the rat. The mode of its action has also been discussed in a previous paper. 1 The normal pupil of the rat is constricted, due to the powerful sphincter tone of the iris. The purpose of this investigation is to determine how a naturally dilated pupil (weak sphincter tone) would react to pilocarpine.
Solutions of pilocarpine hydrochloride (2-10%) were instilled into the conjunctival sac of pigmented and albino guinea pigs. Pilocarpine caused in every instance dilation of the pupil and abolished the light reflex. The result was even more striking if the pupil was first reduced in size by sectioning the cervical sympathetic. The same solutions of pilocarpine invariably produced pupillary constriction in rabbits. The pupil dilated by pilocarpine did not react to usual quantities of arecoline, muscarine and physostigmine (0.5-1% solution), the latter drugs acting orthodoxly in normal guinea pigs. Atropine and “sympathomimetic” drugs increased the size of the pupil dilated by pilocarpine.
The section of the short ciliary nerves reverses the pilocarpine action in guinea pigs, its effect being constriction of the pupil. Atropine abolishes the miotic action of pilocarpine in denervated eyes.
Pilocarpine thus produces pupillary dilatation due to paralysis of parasympathetic myoneural junctions in the normal eyes; and constriction due to stimulation of the same junctions in the denervated eye of the guinea pig.
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