Respiratory burst inhibition in human neutrophils by ultra-low doses of [D-Ala2]methionine enkephalinamide.

An ultra-low dose (10(-14) M) of opioid peptide [D-Ala2]methionine enkephalinamide (DAMEA) is found to exert an inhibitory effect on the production of reactive oxygen species (respiratory burst) in human neutrophils. The validity of this phenomenon has been verified in a series of studies that comprised 30 experiments. The inhibition has proved to be statistically significant (P less than 0.001). The dose-response dependence of the effect (10(-15)-10(-9) M) followed a characteristic biphasic pattern (with the maximum effect at ultra-low doses). An opioid antagonist, naloxone partially blocks the inhibitory effect, which indicates that the DAMEA action is at least partially mediated by opioid receptors.