Peptide opioids and morphine effects on inflammatory process

Morphine was found to inhibit human granulocyte aggregation and ATP, thromboxane B2 (TxB2), and leukotriene B4 (LTB4) secretion during cell aggregation. None of the opioid peptides tested [(D-Ala2, D-Leu5)-enkephalin (DADL), (D-Ala2, N-Me-Phe4, Gly-ol5)-enkephalin (DAGO) or dynorphin 1-9 (Dyn 1-9)] was capable of mimicking morphine effects, while Dyn 1-9 per se induced TxB2 and LTB4 secretion from granulocytes. Morphine inhibition of both cell aggregation and ATP, but not of arachidonic acid metabolism product secretion, was prevented by naloxone. The naloxone-sensitive impairment by morphine of CD11b-CD18 complex surface expression observed could play a role in opioid inhibition of granulocyte activation.