The inhibitory role of nitric oxide (NO) in the somatocardiac sympathetic C-reflex in anesthetized rats.
The role of nitric oxide (NO) in the two somatosympathetic reflex arcs, i.e. A- and C-reflexes, was examined using NO synthase (NOS) inhibitor in anesthetized rats. The A- and C-reflex components were recorded from a cardiac sympathetic efferent nerve and elicited by stimulation of myelinated A and unmyelinated C afferent fibers in the left tibial nerve. NG-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, when administered by either intrathecal (i.t.) or into the cisterna magna (i.c.m.) routes, augmented only the C-reflex in a dose-dependent manner. The effective i.t. dose of L-NAME to augment the C-reflex was approximately 1000 times the i.c.m. dose. NG-nitro-D-arginine methyl ester (D-NAME), an isomer of L-NAME, had no effect on either A- or C-reflexes, when administered i.c.m. Neither i.c.m. pre-treatment nor post-treatment with L-arginine, a NOS substrate, influenced either A- or C-reflexes, but i.c.m. pre-treatment with L-arginine abolished the facilitatory effect of L-NAME on the C-reflex. These results suggest that NO, synthesized in the brain stem, plays an inhibitory role in the central modulation of the somatocardiac sympathetic C-reflex. The possibility of movement of L-NAME to the brain stem from the spinal cord is discussed.
D000758:Anesthesia; D000818:Animals; D001120:Arginine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D002946:Cisterna Magna / Q000502:physiology; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D006321:Heart / Q000294:innervation / Q000502:physiology*; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D007278:Injections, Spinal; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000096:biosynthesis / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester