Effect of alpha-2 adrenoceptor antagonists on colonic function in rats.
We studied the effect of alpha-2 adrenoceptor antagonists on colonic function stimulated by water-avoidance stress, 5-hydroxytryptamine (5-HT), bethanechol and castor oil by comparison with the effects of atropine and a 5-hydroxytryptamine 3 (5-HT3) receptor antagonist, ondansetron. Yohimbine, idazoxan and atropine, but not ondansetron, significantly inhibited water-avoidance stress-stimulated faecal excretion. Yohimbine and idazoxan inhibited neither 5-HT- nor bethanechol-stimulated faecal excretion. In contrast, atropine inhibited both 5-HT- and bethanechol-stimulated faecal excretion and ondansetron inhibited 5-HT-stimulated faecal excretion. Yohimbine did not inhibit the incidence of diarrhoea induced by castor oil, but idazoxan significantly inhibited diarrhoea observed during a 1-h period after the administration of castor oil. Both atropine and ondansetron inhibited diarrhoea during a 2-h period after the administration of castor oil. These findings suggest that alpha-2 adrenoceptor antagonists specifically inhibit colonic motor function stimulated by stress in rats.
Yamamoto
O
O
Discovery Research Laboratories, Nippon Shinyaku Co. Ltd., Nishiohji-Hachijo, Minami-ku, Kyoto, Japan. o.yamamoto@po.nippon-shinyaku.co.jp
Niida
H
H
Tajima
K
K
Tanaka
M
M
Makita
Y
Y
Ueda
F
F
Yano
J
J
D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D018723:Bethanechol / Q000494:pharmacology; D002368:Castor Oil; D003106:Colon / Q000187:drug effects* / Q000502:physiology; D003672:Defecation / Q000187:drug effects* / Q000502:physiology; D003967:Diarrhea / Q000139:chemically induced; D016166:Free Radical Scavengers / Q000494:pharmacology; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology; D013315:Stress, Psychological / Q000503:physiopathology*
D058669:Adrenergic alpha-2 Receptor Antagonists; D016166:Free Radical Scavengers; D018721:Muscarinic Agonists; D018723:Bethanechol; D012701:Serotonin; D002368:Castor Oil