EFFECTS OF ADRENALIN AND ACETYLCHOLINE ON ISOLATED IRIS MUSCLE, IN RELATION TO PUPILLARY REGULATION

Abstract

The inhibitory action of adrenalin on the isolated iris sphincter was confirmed, with occasional exceptions. While acetylcholine elicited contraction in the isolated iris sphincter muscle, the sensi- tivity of this tissue to acetylcholine was low. Iris muscle possessed an inherent spontaneous rhythmicity. This inherent rhythmicity was stressed as a possible contributor to hippus which heretofore has been explained as of central origin. The predominant action of adrenalin on isolated iris radial muscle in the dog and rabbit was one of contraction, whereas in the beef eye it most frequently was one of relaxation. The sensitivity of the dilator muscle is much lower than that of the sphincter to both sympatho-mimetic and parasympatho-mimetic substances. Evidence is cited in support of the belief that, in so far as sympatho-mimetic substances are concerned, the pupillary size is regulated largely through the sphincter component.