The effects of (R)-N-(1-methyl-2-phenylethyl) adenosine (L-PIA), a standard A1-selective adenosine agonist on rat acute models of inflammation and neutrophil function.

L-PIA, a standard A1-selective adenosine agonist, was evaluated orally in carrageenan (CRG)- and reverse passive arthus-pleurisy. White blood cell (WBC) and exudate accumulation were assessed four hours after induction of the inflammatory response. L-PIA inhibited WBC accumulation in both models with ID50's of 4.37 and 4.42 mg/kg, respectively. In contrast, exudate was inhibited by L-PIA only in the CRG pleurisy model (ID50 = 1.01 mg/kg). In mechanistic studies, L-PIA reversed the drop in circulating neutrophil count which occurred within 15 minutes after CRG injection, suggesting that L-PIA may inhibit adhesion of the cells to the endothelium. The effects of L-PIA on several parameters of rat neutrophil function were determined. Enzyme release, O2-, TXB2, and LTB4 production were monitored in response to FMLP and opsonized zymosan (SOZ) stimulation. At high concentrations, L-PIA had a mild inhibitory effect on O2- release in response to FMLP and had a moderate effect on arachidonic acid metabolite production in response to both stimuli. The other response were unaffected. These results suggest that L-PIA may prevent diapedisis or neutrophil adhesion to the endothelium, but has a minimal effect on enzyme release, O2-, LTB4 and TXB2 production.