Suppressive effect of beta-endorphin on body shaking response to ice water immersion and synergistic action of vasoactive intestinal peptide on beta-endorphin in anesthetized rats.

The effects of beta-endorphin and vasoactive intestinal peptide (VIP) on the body shaking response to ice water immersion were observed in anesthetized rats. Intraventricular injection of beta-endorphin markedly inhibited body shaking, but gamma- and alpha-endorphin and methionine-enkephalin showed only slight or little effect. VIP also suppressed the body shaking. The inhibitory effect of beta-endorphin and VIP was blocked by naloxone. When small doses of beta-endorphin and VIP which could not affect the shaking behavior by themselves were administered simultaneously, significant suppression occurred, indicating potentiation of the effect of beta-endorphin by VIP.