Influence of serotonin and melatonin on some parameters of gastrointestinal activity

J Pineal Res. 1989;7(4):333-44. doi: 10.1111/j.1600-079x.1989.tb00909.x.


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.

MeSH terms

  • Animals
  • Digestive System / drug effects*
  • Dose-Response Relationship, Drug
  • Drug Implants
  • Feces / analysis
  • Female
  • Gastrointestinal Transit / drug effects
  • Male
  • Melatonin / administration & dosage
  • Melatonin / pharmacology*
  • Mice
  • Serotonin / administration & dosage
  • Serotonin / pharmacology*


  • Drug Implants
  • Serotonin
  • Melatonin