Glucose Metabolism, Lactate, and Ammonia Production by the Human Placenta In Vitro
Ian R. Holzman, Anthony F. Philipps, And Frederick C. Battaglia
Fifteen human placentas were obtained at term. Placental frag- ments were incubated in a bicarbonate-buffered Earle’s solution. Additions of glutamate (1 mM) or glutamine (1 or 2 mM) were made. All incubations showed a net utilization of glucose. There was a striking variability among placentas in the net glucose utilization rate (1.27 pmoles/g/hr-11.44 pmoles/g/hr, coefficient of variation = 62%). The intraplacental coefficient of variation in glucose utilization was only 14%. All placental incubations showed a net production of both lactate (mean = 7.5 pmoles/g placental wet weight/hr) and ammonia (mean = 3.5 prnoles/g placental wet weight/hr). There was no correlation between lactate or ammonia production and glucose utilization. The addition of sodium gluta- mate (1 gmole/ml) produced no change in glucose utilization or ammonia production. The addition of glutamine (1 and 2 pmoles/ ml) produced a significant increase in ammonia production over that found in the controls, but no change in glucose utilization. Incubation with 2 pmoles glutamine/ml demonstrated an increase in lactate production. All incubations showed a striking increase in ammonia concentration after 45 min of incubation.
Individual placentas may differ markedly in their ability to utilize glucose in an in vitro system. Ammonia production may be a normal metabolic endproduct in a tissue lacking an active urea cycle or a byproduct of the purine nucleotide cycle