Enhancement by pain and stress of analgesia produced by epidural sufentanil in the rat.

This study examined whether pain or stress can enhance the analgesic effects of spinally administered opiates. The experiments determined the effects of mechanically produced pain and of the stress of being restrained on the analgesic effects of 0.63 microgram of epidural sufentanil in rats using a tail-withdrawal procedure. The painful, as well as the stressful, conditions appeared to increase the duration of opiate analgesia 3.7- and 3.0-fold, respectively. The data offer initial evidence that pain and other stressful conditions can enhance the analgesia produced by spinally administered opiates.