Inhibitory nerve distribution and mediation of NANC relaxation by nitric oxide in horse airways.
The distribution of inhibitory nerves and the mediator of the inhibitory nonadrenergic noncholinergic (iN-ANC) nervous system were investigated in smooth muscle preparations from seven regions of equine airways. In tissues incubated with atropine and precontracted with histamine, electrical field stimulation produced frequency-dependent relaxation, and the magnitude of the relaxation decreased from trachea to central bronchi and was absent in peripheral airways. The degree of relaxation in bronchi was not simply a function of bronchial size or generation. Propranolol inhibited part of the relaxation only in the cranial trachealis. After propranolol, NG-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, eliminated the remaining relaxation in all preparations. This effect was reversed by L-arginine, the NO precursor, but not by D-arginine. Exogenous NO concentration dependently relaxed trachealis. These results indicate that: 1) adrenergic innervation is limited to cranial trachealis, 2) iNANC nerves supply the trachea and central bronchi, and 3) NO mediates iNANC function.
Yu
M
M
Department of Large Animal Clinical Sciences, Michigan State University, East Lansing 48824.
Wang
Z
Z
Robinson
N E
NE
Leblanc
P H
PH
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D001341:Autonomic Nervous System / Q000502:physiology*; D001980:Bronchi / Q000294:innervation / Q000502:physiology; D004558:Electric Stimulation; D006736:Horses; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000502:physiology; D011433:Propranolol / Q000494:pharmacology; D012143:Respiratory Physiological Phenomena; D012137:Respiratory System / Q000294:innervation*; D014132:Trachea / Q000294:innervation / Q000502:physiology; D019323:omega-N-Methylarginine
D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001285:Atropine; D001120:Arginine; D011433:Propranolol