The effects of intrinsic nitric oxide on cardiac neural regulation in cats.
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.
Yabe
M
M
Department of Anesthesiology and Intensive Care Medicine, Osaka City University Medical School, Osaka, Japan.
Nishikawa
K
K
Terai
T
T
Yukioka
H
H
Fujimori
M
M
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
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