Effects of serotonin, of its biosynthetic precursors and of the anti-serotonin agent metergoline on the release of glucagon and insulin from rat pancreas.
We have evaluated the effect of serotonin (5-HT) and of its biosynthetic precursors 5-Hydroxytryptophan (5-HTP) and tryptophan (TRP) on the release of immunoreactive glucagon (IRG) and insulin (IRI) from isolated islets and pieces of pancrease of the rat. In isolated islets, 5-HT inhibited the IRI response to a high glucose concentration (3.0 mg/ml), without affecting the IRG response to either a low (0.5 mg/ml) or a high glucose concentration; TRP stimulated the IRG and IRI response to the low glucose concentration, while 5-HTP was ineffective. When pieces of pancreas were used, 5-HT and 5-HTP inhibited IRG response to both glucose concentrations, while IRI release was inhibited only by 5-HT. The anti-5-HT agent metergoline enhanced the release of IRG and IRI by pieces of pancreas at both glucose concentrations. The results indicate that exogenous and endogenous 5-HT inhibit basal as well as glucose-mediated IRG and IRI release; that isolated islets are less sensitive than pieces of pancreas to the inhibitory effect of 5-HT and that TRP acts as an amino acid and not as a precursor of 5-HT.
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D000941:Antigens; D004873:Ergolines / Q000494:pharmacology*; D005934:Glucagon / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D008297:Male; D008711:Metergoline / Q000494:pharmacology*; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*; D014364:Tryptophan / Q000494:pharmacology*
D000941:Antigens; D004873:Ergolines; D007328:Insulin; D008711:Metergoline; D012701:Serotonin; D014364:Tryptophan; D005934:Glucagon; D006916:5-Hydroxytryptophan; D005947:Glucose