Stimulatory influences of calcium channel antagonists on stress-induced opioid analgesia and locomotor activity.

The effects of the calcium channel antagonists diltiazem, nifedipine and the calcium channel agonist, BAY K 8644, on immobilization-induced opioid analgesia and locomotor activity were examined in CF-1 and C57BL strains of mice, respectively. The calcium channel antagonists enhanced the experimenatlly induced analgesia and activity, whereas the agonist reduced these responses. In addition, the calcium channel antagonists augmented, while the agonist attenuated, the analgesic effects of the specific mu and delta opioid agonists, DAGO and [D-Pen2,D-Pen5]-enkephalin (DPDPE), respectively. These results indicate that calcium channel antagonists have facilitatory and/or modulatory effects on the behavioral and physiological consequences of endogenous mu and delta opioid activity.