Free and Bound Tryptophan in Human Plasma During the Perinatal Period

Abstract

The concentration of tryptophan and the degree of binding of the amino acid to protein were examined in human plasma during the perinatal period. Both total and unbound (free) tryptophan were higher in cord vein plasma than in the maternal circulation, the concentration gradient being approximately 1 : 2. The proportion of the total plasma tryptophan concentration that was not bound to protein was less in cord vein plasma than in the maternal circulation. After birth the proportion in infant plasma fell significantly. Both total and free tryptophan fell during the first 24 hours of postnatal life. Total tryptophan returned to the cord vein plasma level 6--8 days after birth whilst free tryptophan failed to increase during the period of the observations. In premature infants total and free tryptophan also declined in concentration 12--24 hours after birth, suggesting the phenomenon to be related to birth rather than to gestational age. Phenylalanine remained unchanged whilst tyrosine increased in concentration during the first 80 hours of postnatal life. Thus, the availability of tryptophan to the tissues appears to decline during the immediate postnatal period and the results suggest that the requirement for tryptophan during this time may exceed the supply from standard artifical milk preparations.

Levels of Total and Free Tryptophan in Maternal and in Umbilical Blood of Infants Born by Vaginal Delivery and by Elective Cesarean Section

“…This fact seems of particular interest especially in consideration of the fre quent utilization of elective cesarean section [25]. Furthermore, the homogeneity ob served in our results suggests that more atten tion should be paid to investigating the sup ply and utilization of tryptophan by the mother and neonate, taking into account the difference in stress, food composition, drugs administered and day-night rhythms of indi vidual mothers and neonates after particular perinatal medical procedures.…”

“…Recently, Tricklebank et al [25] and De Antoni et al [5] have found that in vaginal births the levels of both total and free trypto phan are higher in the umbilical cord than in the mother's blood at a rate of 2:1, while the percentage of free tryptophan is slightly lower in the umbilical than in the maternal plasma [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24],…”

“…The fetus synthesizes its own tissue pro tein mostly from essential amino acids trans ported from maternal to fetal circulation across the placenta, which concentrates them against a chemical gradient [24][25][26]. The knowledge of the nature and control of this transport system is important in order to understand the correlation with fetal nutri tion and growth, in particular if we consider that each tissue concentrates amino acids dif ferently, and that the availability along with the increased uptake of amino acids is ac companied by an acceleration of all endocellular reactions related to them [11,15,16].…”

Free and Bound Tryptophan in Human Milk during Early Lactation

“…As trypto phan is an essential amino acid and crosses the hematoencephalic barrier only in the free form, the high percentage of the free form seems to guarantee a quota available for up take by the central nervous system after sud-den removal of the placenta supply line at birth [9,10]. This full homeostatic motherfetus adjustment is of particular interest, considering that the developing central ner vous system is sensitive to biochemical stress, and the role of this amino acid is important in the control of serotonin synthe sis in the brain [3,7], If we consider the needs of newborn in fants, it is known that human milk may satisfy a number of important criteria.…”

“…Studies on maternal, fetal and neonatal plasma have often tended to exclude trypto phan for methodological reasons, and no re ports have previously examined free trypto phan in maternal milk [6,9,10]. Conse quently little is known of the feeding factors that may influence its availability after the postnatal plasma decline of both total and free forms, following the sudden removal of the placental supply route [3,8], This information would be of clinical sig nificance, considering that tryptophan is the only amino acid that is bound to circulating plasma albumin between 80 and 90% and that the availability of the small free fraction appears to be an important factor in the con trol of the synthesis of the neurotransmitter serotonin in the brain [4,5,7], We evaluated total (protein-bound and free) and free tryptophan levels of breast milk obtained by a standard technique in a group of mothers during the first weeks of lactation.…”