title: Orally administered tryptophan and experimental type 2 diabetes.
abstract: 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.
authors.affiliation: Departamento Fisiología, Facultad de Medicina, Universidad de Extremadura, Badajoz, Spain. matormo@unex.es
authors.forename: M A
authors.initials: MA
authors.lastname: Tormo
authors.forename: A
authors.initials: A
authors.lastname: Romero de Tejada
authors.forename: I
authors.initials: I
authors.lastname: Morales
authors.forename: S
authors.initials: S
authors.lastname: Paredes
authors.forename: S
authors.initials: S
authors.lastname: Sánchez
authors.forename: C
authors.initials: C
authors.lastname: Barriga
authors.forename: R
authors.initials: R
authors.lastname: Hernández
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D001786:Blood Glucose / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002374:Catalase / Q000032:analysis / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000139:chemically induced / Q000378:metabolism*; D004326:Drinking / Q000187:drug effects; D004435:Eating / Q000187:drug effects; D004912:Erythrocytes / Q000737:chemistry / Q000201:enzymology; D007328:Insulin / Q000097:blood / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000097:blood / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013482:Superoxide Dismutase / Q000032:analysis / Q000378:metabolism; D014364:Tryptophan / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D001786:Blood Glucose; D007328:Insulin; D014364:Tryptophan; D002374:Catalase; D013482:Superoxide Dismutase; D008550:Melatonin