Differential control of renal vs. adrenal sympathetic nerve activity by NTS A2a and P2x purinoceptors.

Activation of adenosine A2a and ATP P2x purinoceptors in the subpostremal nucleus tractus solitarii (NTS) via microinjection of the selective agonists CGS-21680 and alpha,beta-methylene ATP (alpha, beta-MeATP), respectively, elicits large dose-dependent decreases in arterial pressure and heart rate, differential regional vasodilation, and differential inhibition of regional sympathetic outputs. With marked hypotensive hemorrhage, preganglionic adrenal sympathetic nerve activity (pre-ASNA) increases, whereas renal (RSNA) and postganglionic adrenal sympathetic nerve activity (post-ASNA) decrease. In this setting, adenosine levels in the brain stem increase. Therefore, we investigated whether stimulation of specific purinoceptors in the NTS may evoke differential sympathetic responses. RSNA was recorded simultaneously with pre-ASNA or post-ASNA in chloralose-urethan-anesthetized male Sprague-Dawley rats. CGS-21680 (2 and 20 pmol in 50 nl) inhibited RSNA and post-ASNA, whereas pre-ASNA increased markedly. alpha,beta-MeATP (25 and 100 pmol in 50 nl) inhibited all sympathetic outputs. Sinoaortic denervation plus vagotomy markedly prolonged the responses to P2x-purinoceptor stimulation. Glutamate (100 pmol in 50 nl) caused differential inhibition of all sympathetic outputs similar to that evoked by alpha,beta-MeATP. We conclude that NTS A2a-purinoceptor activation evokes differential sympathetic responses similar to those observed during hemorrhage, whereas P2x-purinoceptor and glutamate-receptor activation evokes differential inhibition of sympathetic outputs similar to arterial baroreflex responses.