Potentiation of thermoregulatory and analgesic effects of morphine by calcium antagonists.

Diltiazem, a calcium slow channel blocker, greatly potentiated and prolonged the antinociceptive effect of morphine in rats. Hypothermia, the primary thermoregulatory effect of morphine, was also potentiated. Verapamil, another calcium blocker elicited corresponding changes in the analgetic and thermoregulatory effects of morphine. These findings seem to be in concert with the suggestions that opiate effects on thermoregulation and nociception are exerted via modulation of calcium fluxes across neural membranes.