Fig. 5.  Naloxone and norbinaltorphimine, but not sulpiride, block the dilation effects of salvinorin A (n = 5). (A ) Naloxone and methionine enkephalin (Met-enk), but not isoprotenol, block the dilation effects of salvinorin A. (B ) Norbinaltrophimine blocks the dilation effects of salvinorin A. (C ) Sulpiride did not block the dilation effects of salvinorin A.