Placental transfer of taurine in the rhesus monkey.

Maternal to fetal transfer of taurine was examined in 10 pregnant monkeys infused with taurine. In four animals infused at 15 mg/kg body weight, maternal plasma taurine concentration increased from preinfusion values of 8.82 +/- 2.61 to 28.0 +/- 6.00 mumol/dl (mean +/- SD) by the end of the 2-h infusion period. Mean (+/- SD) fetal plasma taurine concentration increased concomitantly, rising from preinfusion values of 13.3 +/- 2.61 to 36.6 +/- 17.8 mumol/dl at the end of the infusion, maintaining the normal fetal to maternal plasma ratio of 1.3 to 1.5. Maternal infusion of larger quantities of taurine increased both maternal and fetal plasma taurine levels; however, the placenta was unable to maintain the normal fetal to maternal gradient. In four monkeys infused with taurine at 25 mg/kg body weight over a 2-h period, mean (+/- SD) maternal plasma taurine concentration increased from 10.0 +/- 1.33 to 43.5 +/- 11.0 mumol/dl. Fetal plasma concentration increased from 13.6 +/- 1.05 to 34.9 +/- 5.89 mumol/dl. However, the maternal to fetal plasma taurine ratio fell from 1.36 to 0.80. Similar results were noted in single animals infused with taurine at 50 and 250 mg/kg body weight. Maternal and fetal plasma concentrations of most other amino acids were not affected by taurine infusion. Fetal, but not maternal, plasma alanine concentration increased after taurine infusion. These data indicate that taurine is efficiently concentrated to the fetal circulation at postprandial maternal plasma taurine concentrations.