Antagonism of Opiate Mydriasis in Mice

Abstract

I 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.

Modulation of Ocular Hydrodynamics and Iris Function by Bremazocine, a Kappa Opioid Receptor Agonist

“…As alluded to before, some investigators believe that opioids also have a peripheral mechanism of action (Nomof, Elliot and Parker, 1968;Drago et al, 1980). Mydriasis also appears to be a speci®c opioid effect as it can be antagonized by naloxone (Klemfuss et al, 1979;Korczyn and Rock, 1981). The mydriasis caused by morphine is thought to be due both to a central mechanism of action (Oldendorf et al, 1972) and to a direct action on the iris (Korczyn and Maor, 1982).…”

Opioid Mydriasis: Cross-Tolerance between Morphine and Enkephalins

“…We have previously shown that this is primarily a central effect [Korczyn and Maor, 1981], easily antagonized by naloxone [Korczyn and Rock, 1981], Enkephalins can also cause naloxone-sensitive mydriasis , It was also demon strated that tolerance develops to the pupil- Fig. 3.…”

“…In several species, how ever, opiates cause mydriasis [Klemfuss et al, 1978;Korczyn et al, 1979;Murray et al. 1983], The pupillary effects of opiates are thought to be of central origin [Lee and Wang, 1975;Korczyn and Maor, 1981;Murray et al, 1983], Morphine mydriasis is naloxone-reversible [Korczyn and Rock, 1981], Enkephalins also cause naloxone-sen sitive mydriasis prob ably by acting on opiate receptors in the brain.…”