The Mydriatic Response of Mice to Atropine

Abstract

The time after subcutaneous injection at which atropine produces most mydriasis in male mice increases with increased body-weight. If the response is measured when it is greatest, and is expressed as a percentage of the maximum mydriatic response obtainable in mice of the weight-range used, the mydriatic response to a dose of atropine is constant in male mice weighing from 16 to 50 g. The time-courses of the mydriatic response to atropine in mice of widely differing weights are parallel to the time-courses of the atropine concentration in the cardiac blood of the mice of the same weight-range given a high dose of atropine subcutaneously. The mydriatic response to atropine is found to be increased at times of poor ambient lighting (such as dusk): if however the mice are tested under conditions of artificial lighting (supplemented by daylight when present), the mydriatic response to a standard dose of atropine is nearly constant at all times from 8 a.m. to 2 a.m.