Opiate receptor interactions of benzomorphans in rat brain homogenates.

Minor structural variations of benzomorphans 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 in 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.