Effect of Dietary 5-Hydroxy-L-Tryptophan for Prevention of Scoliosis in Tryptophan-Deficient Chum Salmon Fry

Abstract

Tryptophan (Trp)-deficient diets (Trp 50mg/100g diet) supplemented with graded levels of 5-hydroxy-L-tryptophan (5-HTP; 0.1, 1, 10 & 100mg/100g diet) were fed to chum salmon fry Oncorhynchus keta to clarify whether 5-HTP, the precursor of serotonin (5-HT), prevents scoliosis caused by Trp deficiency and affects the levels of neurotransmitters in fish brain. The administration of the dose of less than 10mg of 5-HTP/100g diet caused scoliosis in 62-65% of fish atfer 4 weekrearing, whereas the increase in dietary level of 100mg reduced this value to 1.7%. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) contents in the brain of the fish fed Trp-deficient diet containing 100mg 5-HTP/100g diet as well as those of Trp-sufficient diet (Trp 290mg/100g diet) were higher than those of the other dietary groups. The brain norepinephrine (NE) contents showed a tendency to rise as the supplemental level of 5-HTP increased. These results clearly indicate that the oral administration of 5-HTP up to the level of 100mg/100g dict or 40mg/kg body weight/day can almost completely prevent occurrence of scoliosis. Incidence of scoliosis in the fish fed Trp-free diet (Trp 0%) was only 15% even though brain 5-HT content of this group was in the same range as those fed Trp-deficient diet containing supplemental 5-HTP up to 10mg/100g diet. However, the brain NE and dopamine contents of the former were almost the same as those fed Trp-sufficient diet. These findings suggest that catecholamine may be also involved in an occurrence of scoliosis and that there is a considerable physiological difference between complete absence of Trp and intake of small quantity of Trp.