The role of nitric oxide in serotonin-induced relaxations in the canine terminal ileum and ileocolonic junction.
The role of nitric oxide (NO) in 5-HT-induced non-adrenergic non-cholinergic (NANC) relaxations was studied on circular muscle strips of the canine ileocolonic junction (ICJ) and terminal ileum. During an acetylcholine-induced contraction, NO (10(-5) M) evoked a transient relaxation, whereas 5-HT (10(-4) M) caused an initial NANC relaxation followed by a contraction. This initial relaxation to 5-HT, but not the relaxation to NO, was significantly inhibited by the stereospecific inhibitors of the NO biosynthesis NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NNA). L-arginine, but not D-arginine, prevented the inhibitory effect of L-NMMA and L-NNA. The enantiomer of L-NMMA, D-NMMA, had no effect. Hemoglobin abolished the NO-induced relaxations and significantly inhibited the relaxation to 5-HT. From these experiments it is concluded that the 5-HT-induced NANC relaxation is mediated by NO or a NO releasing substance.
Bogers
J J
JJ
Division of Gastroenterology, Faculty of Medicine, University of Antwerp (UIA), Belgium.
Pelckmans
P A
PA
Boeckxstaens
G E
GE
De Man
J G
JG
Herman
A G
AG
Van Maercke
Y M
YM
D000109:Acetylcholine / Q000037:antagonists & inhibitors; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D046508:Culture Techniques; D004285:Dogs; D005260:Female; D007082:Ileum / Q000187:drug effects; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009566:Nitrates; D017942:Nitric Acid; D009569:Nitric Oxide / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology*; D019323:omega-N-Methylarginine
D009566:Nitrates; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D012701:Serotonin; D017942:Nitric Acid; D001120:Arginine; D000109:Acetylcholine