Endogenous nitric oxide derived from NOS I or II in thoracic spinal cord exerts opposing tonic modulation on sympathetic vasomotor tone via disparate mechanisms in anesthetized rats.
The sympathetic preganglionic neurons (SPN) in the thoracic spinal cord regulate vasomotor tone via norepinephrine released from sympathetic terminals and adrenal medulla. We assessed the hypothesis that nitric oxide synthase I (NOS I)- and NOS II-derived nitric oxide (NO) in the thoracic spinal cord differentially modulate sympathetic outflow and that the adrenal medulla may be involved in those modulatory actions. In Sprague-Dawley rats, NOS I immunoreactivity was distributed primarily in the perikaryon, proximal dendrites, or axons of SPN, and small clusters of NOS II immunoreactivity impinged mainly on the circumference of SPN. Intrathecal administration of 7-nitroindazole (7-NI), a specific NOS I antagonist, into the thoracic spinal cord significantly reduced arterial pressure, heart rate, and basal or baroreflex-mediated sympathetic vasomotor tone. On the other hand, intrathecal application of S-methylisothiourea (SMT), a specific NOS II antagonist, elevated arterial pressure with a transient reduction of heart rate, induced a surge of plasma norepinephrine, and reduced baroreflex-mediated but not basal sympathetic vasomotor tone. Bilateral adrenalectomy significantly exacerbated the cardiovascular responses to 7-NI but antagonized those to SMT. We conclude that both NOS I and NOS II are present in the thoracic spinal cord and are tonically active under physiological conditions. Furthermore, the endogenous NO generated by NOS I-containing SPN exerts a tonic excitatory action on vasomotor tone mediated by norepinephrine released from the adrenal medulla and sympathetic nerve terminals. On the other hand, NO derived from NOS II exerts a tonic inhibitory action on sympathetic outflow from the SPN that targets primarily the blood vessels.
['Poon|Yan-Yuen|YY|', 'Tsai|Ching-Yi|CY|', 'Cheng|Chung-Dar|CD|', 'Chang|Alice Y W|AY|', 'Chan|Samuel H H|SH|']
D000313:Adrenal Medulla D000315:Adrenalectomy D000818:Animals D001369:Axons D001794:Blood Pressure D001808:Blood Vessels D003712:Dendrites D004791:Enzyme Inhibitors D006339:Heart Rate D007191:Indazoles D007550:Isothiuronium D008297:Male D009474:Neurons D009569:Nitric Oxide D052248:Nitric Oxide Synthase Type I D052247:Nitric Oxide Synthase Type II D009638:Norepinephrine D051381:Rats D017207:Rats, Sprague-Dawley D013116:Spinal Cord D013564:Sympathetic Nervous System D013904:Thoracic Vertebrae D014666:Vasomotor System
vasomotor tone sympathetic preganglionic neurons norepinephrine adrenal medulla blood pressure