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This Article Full Text Full Text (PDF) All Versions of this Article: 297/4/H1478    most recent 00209.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Guo, Z.-L. Articles by Longhurst, J. C. PubMed PubMed Citation Articles by Guo, Z.-L. Articles by Longhurst, J. C.

Nitric oxide in rostral ventrolateral medulla regulates cardiac-sympathetic reflexes: role of synthase isoforms

Susan-Samueli Center for Integrative Medicine and Department of Medicine, School of Medicine, University of California, Irvine, Irvine, California

Submitted March 4, 2009 ; accepted in final form August 6, 2009

Our previous studies have shown that nitric oxide (NO) synthase (NOS)-containing neurons in the rostral ventrolateral medulla (rVLM) are activated during cardiac sympathoexcitatory reflexes (Refs. 12 and 13). However, the precise function of NO in the rVLM in regulation of these reflexes has not been defined. Three isoforms of NOS, including neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS), are located in the rVLM. We explored the role of NO, derived from different NOS isoforms in the rVLM, in processing cardiac-sympathetic reflexes using whole animal reflex and electrophysiological approaches. We found that, in anesthetized cats, increased mean arterial blood pressure and renal sympathetic nerve activity elicited by epicardial application of bradykinin (BK; 1–10 µg/ml, 50 µl) were significantly attenuated following unilateral rVLM microinjection of the nonselective NOS inhibitor, N-nitro-L-arginine methyl ester (50 nmol/50 nl), or a specific nNOS inhibitor, 7-nitroindazole (7-NI; 5–10 pmol/50 nl; both P < 0.05). In contrast, the responses of mean arterial blood pressure and renal sympathetic nerve activity to cardiac BK stimulation were unchanged by unilateral rVLM microinjection of N-nitro-D-arginine methyl ester (inactive isomer of N-nitro-L-arginine methyl ester, 50 nmol/50 nl), 3–6% methanol (7-NI vehicle), N⁶-(1-iminoethyl)-L-lysine (250 pmol/50 nl; iNOS inhibitor), or N⁵-(1-iminoethyl)-L-ornithine (250 nmol/50 nl; eNOS inhibitor). Furthermore, in separate cats, we noted that iontophoresis of 7-NI (0.1 mM) reduced the increased discharge of cardiovascular sympathoexcitatory rVLM neurons in response to cardiac stimulation with BK (P < 0.05). These neurons were characterized by their responses to inputs from baroreceptors, and their cardiac rhythmicity was determined through frequency and time domain analyses, correlating their discharge to arterial blood pressure and cardiac sympathetic efferent nerve activity. These data suggest that NO, specifically nNOS, mediates sympathetic cardiac-cardiovascular responses through its action in the rVLM.

heart; cardiovascular reflex; nitric oxide synthase