Total and free tryptophan levels in serum of newborn infants. Relationships with the Serotonin and nicotinic acid pathways.

The levels of total and free serum tryptophan have been determined in a group of newborn babies at birth, one day later and five days after birth. Total and free tryptophan levels are very high in the umbilical cord at birth, decrease quickly and significantly 24 hours after birth and show a slight, but not significant increase five days after birth. The high tryptophan levels at birth and their decrease in the first day after birth recall previous data on tryptophan metabolism "via" serotonin and "via" nicotinic acid. Since the synthesis of cerebral serotonin depends on the availability of tryptophan, and is thus linked to the level of free tryptophan in blood, these data suggest that synthesis of serotonin as well may be elevated at birth and may reach the values of adult soon afterwards. With respect to the nicotinic acid pathway the high levels of tryptophan in blood may be related to the synthesis of tryptophan pyrrolase, which is present in the liver of newborn babies.