title: The effects of intrinsic nitric oxide on cardiac neural regulation in cats.
abstract: In this study, we aimed to elucidate the effects of intrinsic nitric oxide (NO) on cardiac neural regulation. Twenty-two cats were anesthetized with 1.5% isoflurane and allocated to Group I (intact; n = 7), Group D (denervated baroreceptors and vagi; n = 8), or Group B (autonomic blockade with i.v. hexamethonium, propranolol, and atropine; n = 7). Cardiac sympathetic nerve activity (CSNA), mean arterial pressure (MAP), sinus heart rate (HR), and A-H and H-V intervals during pacing (150 bpm) were measured before and after i.v. administration of a NO synthase inhibitor, NG-nitro-L-arginine (L-NNA, 30 mg/kg) and after reversal with an excessive dose of L-arginine (300 mg/kg), before and during intermittent electrical stimulation of the posterior hypothalamus. L-NNA significantly increased MAP in Groups I and B, but not in Group D. L-NNA significantly decreased HR and lengthened A-H in Group I, but not in other groups. L-arginine further decreased HR and lengthened A-H unexpectedly. The reasons for these findings could not be determined in this study. L-NNA did not change CSNA. Hypothalamic stimulation did not potentiate L-NNA-induced changes in CSNA, hemodynamic variables, and atrioventricular conduction. In conclusion, intrinsic NO may modulate atrioventricular conduction and sinus rate through a vagal cholinergic, rather than a nonautonomic mechanism.
  
  
  CONCLUSIONS
  Elucidating the roles of intrinsic nitric oxide (NO) on cardiac neural regulation is important. In intact, vagotomized, and baroreceptor-denervated or pharmacologically autonomic blockaded cats, an NO synthesis inhibitor was administered, and atrioventricular conduction and cardiac sympathetic neural discharge were measured. The results suggest a vagal cholinergic mechanism of intrinsic NO.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Osaka City University Medical School, Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yabe
authors.forename: K
authors.initials: K
authors.lastname: Nishikawa
authors.forename: T
authors.initials: T
authors.lastname: Terai
authors.forename: H
authors.initials: H
authors.lastname: Yukioka
authors.forename: M
authors.initials: M
authors.lastname: Fujimori
mesh_terms: D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001283:Atrioventricular Node / Q000187:drug effects / Q000502:physiology*; D001285:Atropine / Q000008:administration & dosage; D001341:Autonomic Nervous System / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002036:Bundle of His / Q000187:drug effects / Q000502:physiology; D002304:Cardiac Pacing, Artificial; D002415:Cats; D002799:Cholinergic Fibers / Q000502:physiology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005730:Ganglionic Blockers / Q000008:administration & dosage; D006339:Heart Rate / Q000187:drug effects; D018738:Hexamethonium / Q000008:administration & dosage; D007031:Hypothalamus / Q000502:physiology; D007530:Isoflurane / Q000008:administration & dosage; D009407:Nerve Block; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D010276:Parasympatholytics / Q000008:administration & dosage; D011311:Pressoreceptors / Q000502:physiology; D011433:Propranolol / Q000008:administration & dosage; D013564:Sympathetic Nervous System / Q000187:drug effects; D013565:Sympatholytics / Q000008:administration & dosage; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D018685:Anesthetics, Inhalation; D004791:Enzyme Inhibitors; D005730:Ganglionic Blockers; D010276:Parasympatholytics; D013565:Sympatholytics; D019335:Nitroarginine; D009569:Nitric Oxide; D018738:Hexamethonium; D001285:Atropine; D001120:Arginine; D011433:Propranolol; D007530:Isoflurane; D019001:Nitric Oxide Synthase