Potentiation of morphine analgesic action in mice by beta-carotene

beta-Carotene was found to potentiate morphine analgesia in hot plate experiments using mice. Response time was increased by about 100%, and the duration of analgesia was markedly prolonged. These features of beta-carotene were a function of the intact molecule, although the closely related compound, alpha-carotene, also exhibited this property. beta-Carotene alone had no effect on the nociceptive response. Other compounds with related structures, metabolic products, or anti-oxidants neither augmented nor antagonized morphine action.