Synergistic action of adenosine and fMet-Leu-Phe in raising cAMP content of purified human monocytes.

The content of cAMP was measured in monocytes treated with fMet-Leu-Phe and adenosine, either singly or in combination. Adenosine caused a small and variable rise in cAMP, which was considerably less than that caused by fMet-Leu-Phe. The rise induced by peptide plus adenosine was twice the sum of the increases caused by each agent alone. An inhibitor of phosphodiesterase also enhanced the adenosine-induced rise in cAMP. The data suggest that the increase in cAMP by adenosine-induced cyclase activation is limited by the activity of phosphodiesterase, and that the latter can be inhibited by fMet-Leu-Phe.