Antagonism of opiate mydriasis in mice.

1 Morphine-induced mydriasis in mice is antagonized by nalorphine, levallorphan and naloxone in a dose-dependent manner. 2 The relative potency of the three agents is 10:56: 134 respectively, thus being in accordance with other tests of narcotic antagonism. Naloxone has the shortest duration of action. 3 When injected into naive animals, nalorphine (but not levallorphan or naloxone) produces a slight mydriasis. 4 Measurement of the diameter of the pupil in mice seems to be a precise, simple and rapid test for studying narcotic antagonist as well as agonist action and has several advantages over standard methods used for this purpose.