The effect of naloxone on the blood levels of morphine and histamine in morphine dependent dogs.

Naloxone administration to morphine dependent dogs has caused an increase in the blood level of morphine, which was transient and statistically significant up to 1 min following the injection of the drug, although concomitant increase in the blood histamine level was not observed. Subsequent injection of naloxone has failed to produce an increase in the blood level of morphine. Likewise, injection of naloxone to morphine dependent dogs pretreated with compound 48/80, a potent mast cell depleter, revealed no increase in the blood level of morphine. This was attributed to the fact that, the origin of morphine, released into the blood, was the mast cells.