Preparations of Rp-cyclic adenosine 3',5'-phosphorothioate (Rp-cAMPS) can contain biologically active amounts of adenosine.

Superoxide anion (O2-.) production from human neutrophils stimulated by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP, 1 microM) was inhibited by preparations of the inhibitor of cAMP-dependent protein kinase, Rp-cyclic adenosine 3',5'-phosphorothioate (Rp-cAMPS, 100 microM). This effect of Rp-cAMPS was reversed by xanthine amine congener (0.1 microM), an adenosine receptor antagonist, and by low concentrations of adenosine desaminase (0.02 mg/ml). HPLC analysis shows that these preparations of Rp-cAMPS contained concentrations of adenosine which could produce significant inhibition of fMLP-induced O2-. production. These results suggest that Rp-cAMPS should be used with caution in cells or tissues containing adenosine receptors, and that preparations of Rp-cAMPS should be treated with adenosine desaminase before use to avoid activation of adenosine receptors.