Adrenergic, cholinergic, and nonadrenergic-noncholinergic intrinsic innervation of the jejunum in horses.
OBJECTIVE
To determine the major neurotransmitters that regulate contractile activity in the jejunum of horses.


METHODS
Jejunal specimens from 65 horses without gastrointestinal tract lesions.


METHODS
Jejunal smooth muscle strips, oriented in the plane of the circular or longitudinal muscular layer, were suspended isometrically in muscle baths. Neurotransmitter release was induced by electrical field stimulation (EFS) delivered at 30 and 70 V intensities and at various frequencies on muscle strips maintained at low or high muscle tone. To detect residual nonadrenergic-noncholinergic neurotransmission, the response of muscle to EFS in the presence of adrenergic and cholinergic blockade was compared with the response in the presence of tetrodotoxin.


RESULTS
Atropine (ATR) decreased the contractile response of muscle strips to EFS under most conditions. However, ATR increased the contractile response of high-tone circular muscle. Adrenergic blockade generally increased the muscle responses to 30 V EFS and in high-tone longitudinal muscle but decreased contractile responses in high-tone circular muscle. Tetrodotoxin significantly altered the responses to EFS, compared with adrenergic and cholinergic receptor blockade.


CONCLUSIONS
Acetylcholine and norepinephrine appear to be important neurotransmitters regulating smooth muscle contractility in the equine jejunum. They induce contraction and relaxation, respectively, in most muscle preparations, although they may cause opposite effects under certain conditions. In addition, nonadrenergic-noncholinergic excitatory and inhibitory influences were detected.


CONCLUSIONS
Acetylcholine or norepinephrine release within the myenteric plexus of horses may alter gastrointestinal motility.
Malone
E D
ED
Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota, St Paul 55108, USA.
Kannan
M S
MS
Brown
D R
DR
Turner
T A
TA
Trent
A M
AM
D018663:Adrenergic Agents / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D018678:Cholinergic Agents / Q000494:pharmacology*; D004558:Electric Stimulation; D006736:Horses / Q000502:physiology*; D007583:Jejunum / Q000294:innervation / Q000502:physiology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D018663:Adrenergic Agents; D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D018678:Cholinergic Agents; D018727:Muscarinic Antagonists; D015016:Yohimbine; D013779:Tetrodotoxin; D001285:Atropine; D011433:Propranolol; D010646:Phentolamine