Opiate receptor interactions of benzomorphans in rat brain homogenates

Minor structural variations of benzomorphan opiates are associated with striking, unpredictable shifts in the relative extent of agonist or antagonist properties in vivo. The relative abilities of a number of benzomorphans to inhibit ³H naloxone binding in the absence and presence of sodium in vitro show some correlations with their pharmacologic properties in vivo, although distinct exceptions exist. The ability of opiate agonists to inhibit ³H naloxone binding is greatly reduced by sodium, while pure antagonists are affected very little, if at all, and mixed agonist antagonist benzomorphans display an intermediate response.