Analgesic effect of morphine: a role for beta-endorphin.

Capsaicin, a neurotoxic agent that induces a decrease in hypothalamic beta-endorphin, a specific antiserum and human beta-endorphin fragment 6 31, a peptidergic beta-endorphin antagonist have been used in the attempt of selectively affecting the function of beta-endorphinergic system and of evaluating the possible role of this peptide in the analgesic effect of morphine. All 3 experimental approaches resulted in a decrease of the analgesia induced by morphine, thus suggesting that beta-endorphin is involved in the effect of morphine.