[Tryptophan metabolism during the perinatal period]

Tryptophan is considered to be an important indicator of nutritional changes during the perinatal period, from fetus to neonate. By means of high performance liquid chromatography (HPLC), we determined the concentrations of both free tryptophan (TRP) and its metabolite, kynurenine (KYN), in maternal venous plasma (M.V.) and umbilical arterial and venous plasma (U.A., U.V.) (n = 45) at the time of delivery. TRP and KYN concentrations were also measured in neonatal venous plasma (n = 11) for 3-5 days following delivery.

1) Day and night plasma TRP levels in non-pregnant women (n = 12), in pregnant women at term before labor (n = 12) and in delivering women (M.V.) (n = 45: day, n = 24: night, n = 21) were significantly different. 2) Both TRP and KYN concentrations were significantly higher in U.A. and U.V. than those in M.V., the concentration gradient being approximately 1:2, and a positive maternal-fetal relationship was observed (r = 0.586-0.944, p less than 0.01). 3) A positive relationship was observed between the venous-arterial gradient of umbilical cord tryptophan and the Kaup Index (r = 0.316, p less than 0.05). 4) In order to minimize individual variations, the ratios of TRP and KYN levels in newborn venous plasma to those in the umbilical arteries were calculated (n = 11). These ratios started to increase at 20-50 hours after delivery, which suggested that the first milk feeding may alter the metabolism of tryptophan in neonates.