Plasma tryptophan/large neutral amino acids ratio in domestic dogs is affected by a single meal with high carbohydrates level

Simple Summary Many studies have reported that aggressive dogs have low serotonin plasmatic levels. l-tryptophan (TRP) is the precursor of serotonin and its availability is affected by five large neutral amino acids (isoleucine + leucine + phenylalanine + tyrosine + valine) (5LNAAs). The passage of TRP through the blood–brain barrier uses carriers, where it competes with 5LNAAs. Hence, a diet modification could be useful to alter their plasma ratio, in improving TRP bioavailability. Five female Labrador Retrievers were fed three different meals: M1 (a mix of puffed rice, minced meat and olive oil), M2 (puffed rice and olive oil) and M3 (commercial dry food usually consumed). Blood was collected right before the first meal (t0) and after 2, 4, 6, 8, 10 and 24 h. Plasmatic TRP concentrations showed no significant difference between M1, M2 and M3 samples. M2 led to a decrease in 5LNAAs levels and consequently led to significant higher TRP/5LNAAs ratios in the 6 h period after the provision of carbohydrates, compared to both M1 and M3. In addition, the mean TRP/5LNAAs ratio was significantly higher in M2 than in M3, at t8 and t10. These results indicate that meal composition affects TRP/5LNAAs ratio and possibly, TRP bioavailability. Abstract Aim of this study was to evaluate the plasma ratio between l-tryptophan (TRP) and five large neutral amino acids (isoleucine + leucine + phenylalanine + tyrosine + valine) (5LNAAs) after a single meal with high carbohydrates level. Five female Labrador Retrievers were involved. Each dog was fed three different meals: M1 (a mix of puffed rice, minced meat and olive oil), M2 (puffed rice and olive oil) and M3 (commercial dry food usually consumed) once in the morning for one single day every 30 days. Blood was collected right before the first meal (t0) and after 2, 4, 6, 8, 10 and 24 h. Plasma amino acids’ concentrations were measured using an HPLC (High-performance liquid chromatography) method with fluorimetric detection. Plasmatic TRP concentrations showed no significant difference between M1, M2 and M3 samples at any sampling time. M2 led to a decrease in 5LNAAs levels and consequently led to a significant higher TRP/5LNAAs ratios in the 6 h period after the provision of carbohydrates, compared to both M1 and M3. In addition, the mean TRP/5LNAAs ratio was significantly higher in M2 than in M3 at t8 and t10. These results indicate that meal composition affects TRP/5LNAAs ratio and possibly, TRP bioavailability.