ABSTRACT
Since L-tryptophan is of importance in the metabolism of many organs, it is understandable that numerous studies have been directed toward determining blood levels of L-tryptophan in humans and in experimental animals under normal and abnormal conditions. These studies have been concerned with learning about conditions whereby blood L-tryptophan levels became altered. Such studies have established normal blood levels in humans and animals and also have revealed blood changes in a variety of altered states. These findings have served to stimulate further investigations into why blood levels of L-tryptophan change and into the possible mechanisms responsible. In this chapter, some human diseases where blood L-tryptophan levels become altered are reviewed, and a few selected examples are cited to stress how this change may occur. Also, a number of experimental animal studies whereby species and agents affect blood L-tryptophan levels are reviewed and possible mechanisms involved are considered.
