Determination of the adenosine A(1) agonist N(6)-cyclopentyladenosine in rat blood by solid-phase extraction and HPLC

A solid-phase extraction procedure has been developed for the isolation of the adenosine A1 receptor agonist N(6)-cyclopentyladenosine from rat blood. The biological samples were spiked with N(6)-cyclopentyladenosine and the analogue N(6)-cyclohexladenosine (internal standard), diluted with sodium hydroxide, loaded onto disposable cartridges with subsequent desorption with methanol and analysis by HPLC. The performance of columns pre-packed with different C18-bonded silica phases or with a polymeric reversed-phase sorbent (Oasis HLB) was assessed. The highest extraction efficiencies (recovery rates>83.3%) for the two N6-alkyl substituted adenosines were achieved by the Oasis HLB cartridges. In addition, the polymeric sorbent provided reproducible recoveries (relative standard deviation<4.8%), whereas large variations (relative standard deviation values, 9--16.3%) in the extraction yields were observed using the conventional silica-based C18 cartridges. The described sample preparation method is rapid, simple, selective and it is suitable for pharmacokinetic studies.