Opioids depress in vitro human monocyte chemotaxis.

Intravenous drug abusers (IDA) normally show functional defects in monocyte activity, in particular their chemotactic response. The aim of the present work was to study the action of several opioids on monocyte chemotaxis. To do so, monocytes from healthy individuals were incubated with heroin and morphine at three different concentrations (10(-5) M, 10(-6) M and 10(-7) M), with the finding of a significant depression in monocyte chemotaxis in all cases. This alteration could be due to a receptor effect or, conversely, to a non-specific effect. Accordingly, in the second phase of the study, monocytes from controls were incubated with a selective agonist of mu receptors (DAGO) and a selective agonist of delta receptors (DPDPE). In both cases a decrease in chemotactic function was observed similar to that following incubation with morphine or heroin. Preincubation of the monocytes with naloxone prevented the depression induced by both specific agonists. These findings suggest that opioids play an important role in the depression of monocyte chemotaxis observed in IDA. The results also suggest the presence of mu and delta opiate receptors in the cells of the phagocytic mononuclear system.