EFFECT OF ENKEPHALINS AND ENDORPHINS ON CYTOTOXIC ACTIVITY OF NATURAL-KILLER-CELLS AND MACROPHAGES MONOCYTES IN MICE/

The effect of [Met(5)]enkephalin, [Leu(5)]enkephalin, proenkephalin, d ynorphin-(1-17) or beta-endorphin on the cytotoxic (Cr-51 release assa y) activity of natural killer cells and macrophages/monocytes was stud ied in mice. It was found that a single i.p. injection of [Met(5)]enke phalin, [Leu(5)]enkephalin, beta-endorphin, dynorphin or proenkephalin as well as repeated treatment with both enkephalins increased natural killer cell activity. In vitro only [Met(5)]enkephalin stimulated nat ural killer cells. Opioid peptides did not affect the cytotoxic activi ty of macrophages/monocytes. In addition to functional alterations, bo th enkephalins and beta-endorphin increased the percentage of cells wi th natural killer phenotype. The results of this study suggest that th e increase in natural killer cytotoxicity after opioid peptides inject ed once or for 14 days may result from an increased number of natural killer cells in the spleen.