Rat liver is not damaged by high dose tryptophan treatment

Adult male Sprague-Dawley rats were treated with USP-grade L-tryptophan at a level of 250 mg/kg seven times over 14 d or three times over 3 d by gastric gavage. At autopsy liver specimens were prepared for histological study by stains specific for lipids, for glycoprotein and glycogen, and for fine structure by electron microscopy. Liver lipid did not accumulate as a result of tryptophan treatment. In a series of unfed animals, however, liver lipid had accumulated within 24 h of food withdrawal. Tryptophan has been implicated in fatty liver development by several reports that cite each other, but, in all cases but one, unfed animals were used, and the data show that liver lipid was already present in the unfed animals at the beginning of the experiment. Tryptophan has also been cited as causing abnormal liver morphology, but our evidence suggests that such observations are the result of artifact induced by frozen section preparation and not the result of tryptophan treatment. Our experiments indicate that tryptophan administered to rats at dosages in excess of those recommended for humans does not induce fatty liver or other morphological changes detectable by the methods described.