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Journal of Pharmacology And Experimental Therapeutics, Vol. 171, Issue 2, 205-213, 1970
Copyright © 1970 by American Society for Pharmacology and Experimental Therapeutics

AN ANALYSIS OF EPHEDRINE MYDRIASIS IN RELATIONSHIP TO IRIS PIGMENTATION IN THE GUINEA-PIG EYE IN VITRO

R. J. SEIDEHAMEL 1, A. TYE 1, and P. N. PATIL 1

1 College of Pharmacy, The Ohio State University, Columbus, Ohio

Isolated albino or pigmented guinea-pig eyes with pupils constricted to a base line with methacholine were exposed to increasing cumulative molar concentrations of mydriatics and the resulting pupilary dilation was measured and plotted in dose-response curves. Pigmented irises were about one-third as sensitive to ephedrine mydriasis as albino irises. This phenomenon of differing iris sensitivity was selective for ephedrine and related compounds having a methyl group on the agr-carbon and a hydroxyl group on the beta-carbon of the side chain. It did not occur with other mydriatics such as phenylephrine, tyramine, isoproterenol or aminophylline. Ephedrine produced mydriasis through a ``direct'' component of action which was not antagonized by propranolol or sotalol (MJ 1999); higher concentrations of ephedrine were antagonized slightly by phentolamine but lower concentrations were not. Mydriasis due to ephedrine therefore involves receptors other than alpha or beta adrenergic. Theories suggested by earlier workers to account for the lesser sensitivity with greater iris pigmentation are not supported by these investigations. The mechanism of the latter phenomenon appears to be closely involved with the mydriatic's molecular structure.

Submitted on April 1, 1969
Accepted on October 16, 1969




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