Influence of serotonin and melatonin on some parameters of gastrointestinal activity.
In vitro melatonin (M) reduced the tone of gut muscles and counteracted the tonic effect of serotonin (5-HT). In vivo 0.1 to 4 mg of 5-HT (contained in beeswax implants) decreased the food transit time (FTT) in a dose-dependent manner, but higher doses (5 and 6 mg) increased the FTT. Melatonin injected intraperitoneally into mice bearing 5-HT implants (2 mg per animal) blocked partly the serotonin effect and increased FTT by 50%; however, no dose-dependent effect was observed when doses between 0.01 and 1 mg were used. Surprisingly, M injected into intact mice decreased FTT to levels comparable to those observed in 5-HT implanted, M-treated mice. Again, this significant decrease was not dose-dependent between 0.02 and 1 mg. Although in vitro the maximal inhibition of serotonin-induced spasm was achieved when the M:5-HT ratio was 50-100:1, in vivo the effective ratio was about 1:1. This may indicate that part of M action on the gut movement is mediated by extraintestinal mechanisms. A hypothetical, counterbalancing system of M and 5-HT regulation of gut activity (similar to adrenaline-acetylcholine system) is proposed.
Bubenik
G A
GA
Department of Zoology, University of Guelph, Ontario, Canada.
Dhanvantari
S
S
D000818:Animals; D004064:Digestive System / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004343:Drug Implants; D005243:Feces / Q000032:analysis; D005260:Female; D005772:Gastrointestinal Transit / Q000187:drug effects; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D051379:Mice; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology*
D004343:Drug Implants; D012701:Serotonin; D008550:Melatonin