Antagonism by naloxone of narcotic-induced respiratory depression and analgesia.

Receptor mechanisms for narcotic-induced respiratory depression and analgesia were compared by apparent pA2 values of morphine-naloxone, levorphanol-naloxone and pentazocine-naloxone. The similarity of apparent pA2 values of the three compunds for respiratory depression suggests that morphine, levorphanol and pentazocine may interact with similar receptors to produce this effect. Significant differences between apparent pA2 values of pentazocine-naloxone and morphine-naloxone or levor-phanol-naloxone for analgesia suggest, as previously shown, that narcotic and narcotic-antagonist analgesics appear to interact with receptors in different manners. Significant differences between apparent pA2 values for respiratory depression and analgesia suggest that these two effects of the narcotic drugs are mediated by different receptor interactions.