MIOSIS AND FLUCTUATION IN RABBIT PUPIL - EFFECTS OF MORPHINE AND NALOXONE

  • 1 January 1977
    • journal article
    • research article
    • Vol. 201  (3) , 587-592
Abstract
In the unanesthetized rabbit, morphine (12-16 mg/kg, i.v.) produced a miosis that was not sustained. The response to the narcotic was a pupillary constriction that became maximal within 2 min following i.v. administration, after which time pupil size fluctuated appreciably. The magnitude of the fluctuation, typically as high as 40% of control diameter, was much larger than can be attributed to noise. The fluctuations occurred within a frequency of about 0.5-2/min. The miosis and subsequent fluctuation seen with 12 and 16 mg/kg of morphine was blocked by naloxone (0.5 mg/kg, i.v.), but 128 mg/kg of morphine overcame the block. Cumulative dose-response curves for morphine and for morphine after naloxone yielded the value pA2 [-log of the apparent Kd] = 6.8 which was in agreement with values obtained using other effects and species. Administration of morphine after exposure to high intensity light produced less miosis than that seen under normal illumination.

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