Uptake of tryptophan into brain of rainbow trout (Oncorhynchus mykiss)

Brain and plasma levels of tryptophan, 30 min after intraperitoneal administration of increased doses of L-tryptophan (0, 12.5, 25, 37.5, 50, 62.5, 75, 87.5, 100, 150, and 200 mg/kg body wt), D-tryptophan (0, 25, 50, 75, 150 mg/kg body wt) or the joint administration of L-tryptophan and L-tyrosine (75 mg/kg body wt), were analyzed spectrofluorimetrically. The results show that the uptake of tryptophan into the brain takes place through a stereospecific and saturable carrier, which is common for tyrosine and possibly other neutral aminoacids, in a way similar to that observed for mammals. On the other hand, the findings indicate that the uptake of tryptophan into brain of rainbow trout seems to be little sensitive to the effects of competition with other amino acids. J. Exp. Zool. 282:285–289, 1998.