Spinal adenosine modulates capsaicin-induced depressor reflex: involvement of adenosine A2 receptor

1. The depressor responses to i.a. and i.v. injection of capsaicin (CAP) were blocked following intrathecal (i.t.) perfusion of [D-Pro2, D-Trp7,9] substance P, a specific substance P antagonist. This confirmed that the CAP-elicited depressor reflex is mediated by substance P-containing afferent fibres. 2. The regulatory roles of spinal adenosine in the CAP-evoked substance P release and the possible involvement of adenosine A2 receptors were analyzed by analyzing the changes in cardiovascular responses to i.a. and i.v. injection of CAP after various pretreatments with adenosine agonists and antagonists, administered subcutaneously or intrathecally.