Intestinal absorption of L-tryptophan in scleroderma

The purpose of this investigation was to study the intestinal absorption of L-tryptophan and to assess the absorptive function of the intestine in scleroderma. The oral L-tryptophan loading test was performed in 31 cases of systemic scleroderma (progressive systemic sclerosis, PSS) and 3 cases of localized scleroderma. Serum levels of tryptophan and urinary excretion of indole-acetic acid (IAA) and indican (IS) were determined in order to assess intestinal absorption of tryptophan. In 10 cases the D-xylose test and in 4 cases Schilling's test was also performed. Furthermore, in vitro binding of L-tryptophan by plasma proteins in PSS and in other skin diseases as controls was studied. The normal increase in serum tryptophan after loading was noted in 17 cases (in 14 cases of PSS with a mild, slow progression in 3 cases of PSS with a severe, rapidly progressing course). In 10 of these cases, urinary excretion of IAA was higher than normal and in normal and in 3 cases excretion of urinary IS was also above normal. On the other hand, in 14 cases of severe, rapidly progressing PSS and in 2 of 3 cases of widespread linear scleroderma, serum levels of tryptophan were markedly depressed after loading, while urinary excretion of IAA and IS was normal. In all 4 cases studied, Schilling's test was normal, and only in 2 of 10 cases of PSS was the D-xylose test abnormal. It is concluded that in the majority of cases of PSS, intestinal absorpiton of tryptophan is normal as also is the absorptive function of the intestine. The slight rise in serum tryptophan after loading in some cases of PSS may be a result of increased binding of tryptophan by albumin.