Molecular and Cellular Biochemistry

, Volume 261, Issue 1, pp 57–61 | Cite as

Orally administered tryptophan and experimental type 2 diabetes

  • M.A. Tormo
  • A. Romero de Tejada
  • I. Morales
  • S. Paredes
  • S. Sánchez
  • C. Barriga
  • R. Hernández


There is a link between diabetes and oxidative stress. Hyperglycaemia leads to free radical generation and alterations of endogenous antioxidants. Our aim is to study the effect of orally administered L-tryptophan (TRP), the melatonin precursor, an endogenous antioxidant, on circulating levels of glycaemia, insulin and melatonin, and on the superoxide dismutase and catalase antioxidant systems in non-diabetic (ND) and type 2 diabetic (n5-STZ) male Wistar rats.

At 19:30 every day for 15 days, TRP (125 mg/kg body weight) was administered orally. At 09:00 every two days the glycaemia was measured and every day the intake of food and water was recorded. At the beginning and end of treatment (at 09:00; 21:00; 02:00) plasma insulin and melatonin levels were measured, and (at 09:00) the enzymatic activities of catalase and superoxide dismutase (SOD) in erythrocytes were also measured. Glycaemia values were greater (p < 0.01) in n5-STZ rats than in ND rats, while insulin levels were lower (p < 0.05) at all times studied and these parameters were not altered by the TRP administration. Melatonin levels at 02:00 were lower in n5-STZ than in ND rats (p < 0.05). The TRP administration did not modify the circulating melatonin levels in ND rats, but raised (p < 0.01) the levels at 02:00 in the treated n5-STZ group. In ND rats after TRP administration there was a decline in catalase activity (p < 0.05), while in n5-STZ rats there was a rise (p < 0.01) at the end of treatment. However, there were no significant changes in SOD activity. There was increased food intake (g/day) in the treated n5-STZ group (p < 0.01). In conclusion, the oral administration of TRP did not modify glycaemia or insulinaemia levels, but raised melatonin levels in diabetic rats at 02:00, lowered catalase activity in ND rats but raised it in n5-STZ rats, and increased food intake in n5-STZ rats. (Mol Cell Biochem 261: 57–61, 2004)

catalase food intake glycaemia insulin L-tryptophan melatonin superoxide dismutase type 2 diabetes 


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Copyright information

© Kluwer Academic Publishers 2004

Authors and Affiliations

  • M.A. Tormo
    • 1
  • A. Romero de Tejada
    • 1
  • I. Morales
    • 1
  • S. Paredes
    • 1
  • S. Sánchez
    • 1
  • C. Barriga
    • 1
  • R. Hernández
    • 1
  1. 1.Departamento Fisiología, Facultad de MedicinaUniversidad de ExtremaduraBadajozSpain

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