Activation of NTS A2a Adenosine Receptors Impairs Cardiopulmonary Chemoreflex Control of Renal (RSNA), Adrenal (ASNA) and Lumbar (LSNA) Sympathetic Nerve Activity

Abstract

Activation of NTS A2a adenosine receptors increases ASNA, decreases RSNA and does not alter LSNA (Clin Exp Physiol Pharmacol 28: 120–124, 2001). A similar pattern of regional sympathetic responses was occasionally observed following activation of cardiopulmonary chemoreceptors. As A2a adenosine receptors may facilitate neurotransmitter release it was likely that these receptors may facilitate the cardiopulmonary chemoreflex. In the present study we compared the regional sympathetic responses evoked by right atrial injections of 5HT3 receptor agonist, phenylbiguanide (PBG, 1–8 μg/kg), before and after stimulation of NTS A2a adenosine receptors (microinjections of CGS21680, 20 pmol/50 nl) in urethane/chloralose anesthetized rats (n=7). Activation of cardiopulmonary chemoreceptors evoked differential, dose dependent sympathoinhibition RSNA>ASNA>LSNA). Surprisingly, the responses in all sympathetic outputs (Δ%) were similarly attenuated following stimulation of NTS A2a adenosine receptors (−95.5±1.8 vs. −60.3±5.3, −74.9±7.1 vs. −44.6±8.6, −56.4±3.6 vs. −34.61±5.6, for RSNA, ASNA and LSNA, respectively, at the maximal dose of PBG). We conclude that A2a adenosine receptors may facilitate NTS neurons/terminals which inhibit cardiopulmonary chemoreflex pathway. NIH HL‐67814