Role of alpha-2 adrenoceptors in regulation of giant migrating contractions and defecation in conscious dogs.
The aim was to investigate the effects of alpha(2)-adrenoceptor antagonist yohimbine on colonic motility and defecation. The effects of yohimbine (0.5, 1.0, and 3.0 mg/kg) on colonic motility and defecation were studied in neurally intact dogs (N=6), dogs with extrinsic denervation of the ileocolon (N=4), and dogs with enterically isolated ileocolnic loops (N=5) equipped with strain gauge force transducers on the ileocolon. The effects of yohimbine on colonic motility and defecation were also studied in the presence of various antagonists (atropine, hexamethonium, ondansetron, FK224, and naloxone). Yohimbine evoked giant migrating contractions and defecation in a dose-independent manner in neurally intact dogs. These stimulatory effects of yohimbine were abolished by atropine and hexamethonium. In dogs with extrinsic denervation, yohimbine induced giant migrating contractions in the colon but did not stimulate defecation. In dogs with ileocolonic loops, yohimbine induced colonic motor complexes but not giant migrating contractions in the enterically isolated colon. These results indicate that alpha(2)-adrenoceptors in the peripheral nervous system regulate giant migrating contractions by controlling the release of acetylcholine, while those in the central nervous system must be important in the regulation of defecation.
Nagao
Munenori
M
Division of Biological Regulation and Oncology, Department of Surgery, Tohoku University Graduate School of Medicine, Sendai 980-8574, Japan.
Shibata
Chikashi
C
Funayama
Yuji
Y
Fukushima
Kouhei
K
Takahashi
Ken Ichi
KI
Jin
Xue Lin
XL
Kudoh
Katsuyoshi
K
Sasaki
Iwao
I
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000294:innervation / Q000378:metabolism / Q000502:physiology*; D003242:Conscience; D003672:Defecation / Q000187:drug effects / Q000502:physiology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D017933:Peripheral Nervous System / Q000378:metabolism*; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine