Cyclic Adenosine Monophosphate in Phagocytizing Granulocytes and Alveolar Macrophages

The ingestion of particles by phagocytizing cells is accompanied by marked changes in such metabolic parameters as oxygen consumption, glycolysis, glycogenolysis, H202 production, and activity of the hexose-monophosphate shunt, with the extent of these events depending on the particular cell type studied (for references see 1, 4, 6, 7) . In general, these metabolic changes can be observed within a few minutes or less after the addition of particles and are considered to reflect an increased energy demand during phagocytosis . It is not clear, however, in which way the contact of particles with the outer membrane or the initial phase of phagocytosis is signaled to the interior of the cell, where these metabolic changes take place . It is now well established that the interaction of many hormones with specific receptor sites at the outer membrane is signaled to the interior by changes in the intracellular concentration of adenosine 3',5'-monophosphate (Ado-3',5'-P, cyclic AMP) via stimulation of the membrane-located adenylate cyclase (13) . This system is not restricted to hormone effects, e.g., lymphocytic transformation by stimulation of phytohemagglutinins (13) . It was therefore tempting to speculate that cyclic AMP may have a messenger function in the process of phagocytosis . Indeed, results presented by Park et al. (11) suggest that during phagocytosis of polystyrene-latex particles by crude leukocyte preparations, the intracellular concentration of cyclic AMP is increased . Similar results were reported by Manganiello et al . (9) . It was not clear, however, whether the observed increase in cyclic AMP concentration was in fact related to phagocytosis . On the other hand, Stossel and colleagues (14) were unable to detect significant changes of cyclic AMP concentration in phagocytizing guinea pig peritoneal leukocytes . In view of these conflicting observations, it was of interest to reinvestigate the possible participation of cyclic AMP in the phagocytosis of polystyrene-latex particles by two different cell types, pig peripheral leukocytes and rabbit alveolar macrophages .