A SOURCE OF ADENOSINE INVOLVED IN CARDIOVASCULAR-RESPONSES TO DEFENSEAREA STIMULATION

We have investigated the source of central adenosine important in modu lating the cardiovascular response to hypothalamic defense area (HDA) stimulation in alpha-chloralose-anesthetized rats. Microinjections of an ecto-5'-nucleotidase inhibitor, alpha,beta-methylene ADP (alpha,bet a-meADP), were made into caudal nucleus of the solitary tract (cNTS) a nd rostral ventrolateral medulla (RVLM), and its effects on HDA-evoked responses were observed. Stimulation of KDA evoked an increase in art erial pressure and a secondary rise in arterial pressure after stimula tion ceased. There was also an increase in heart rate and hindlimb blo od flow. alpha,beta-meADP had no effect on resting levels of arterial pressure, heart rate, and hindlimb blood flow when injected into the c NTS or RVLM. alpha,beta-meADP also had no effect on the HDA-evoked tac hycardia and increase in muscle blood flow. However, alpha,beta-meADP reduced the primary increase in arterial pressure evoked by HDA stimul ation when microinjected into the cNTS. In contrast, alpha,beta-meADP reduced the secondary increase in arterial pressure when microinjected into the RVLM. From these results, we suggest that at least part of t he adenosine released centrally during HDA stimulation is derived extr acellularly from ATP metabolism.