L-tryptophan supplementation increases serotonin blood levels in dogs fed a dissociated carbohydrate-based diet.

Abstract

The aim of the present study was to verify the effect, on blood serotonin (5-HT) concentrations of the addition of L-Tryptophan (L-TRP) to a dissociated diet, in the meal consisting only of the carbohydrate component. For this study were recruited, from a public shelter, 6 dogs (5 males and 1 neutered females), weighing between 15 and 30 kg and living in the shelter for more than six months. The dogs were fed 2 daily meals (at 8.00 A.M. and 4.00 P.M.). The morning meal was a carbohydrate-based one (puffed rice), integrated with 1mg/kg of L-TRP, whereas the evening meal was composed by the commercial diet previously eaten during the adaptation period. Blood was collected the day before the first administration of the diet (T0) and at the 21th (T1), 30th (T2) day of the treatment, after 8 hours from carbohydrate meal. A further blood sample was collected 14 days after the suspension of the diet (T3).

As regards TRP, the statistical analysis revealed a significant difference between the blood concentrations at T3 and those determined at T1 (Z = -2.201; p = 0.028) and at T2 (Z = -2.201; p = 0.028).

About 5-HT concentrations, statistical analysis, performed with the Newman Keuls’s test, has revealed a significant difference between the concentrations at T1 and at T0 (q= 4.43; p<0.05). Also, the concentration at T2 is significant different by those at T3 (q= 3.16; p<0.05) and at T0 (q= 4.43; p<0.05).

The data obtained, albeit carried out on a small number of animals, however kept in the same environmental and feeding situation, showed that the blood levels of TRP could be correlated with those of 5-HT. Furthermore, the determination of 5-HT concentrations in blood serum seems to provide a faithful image of the cerebral metabolism of this amine, as increases in circulating TRP concentrations is followed by significant increases in 5-HT.