Glucose Consumption and Lactate Production of Human Placental Tissue Under Different Conditions of In Vitro Incubation

Abstract

Objective: To assess the glycolytic activity of human placental tissue in the third trimester as measured by glucose consumption and lactate production under different conditions of in vitro incubation.

Method: An incubation technique was used to study the metabolic activity of the human placenta by comparing large blocks (0.3 cm³, T1) and small fragments (explants, 0.03 cm³, T2). Placentas were obtained from premature (28-33 weeks) and term (39-41 weeks) deliveries. In addition, different experimental conditions were used to investigate the influence of incubation medium (Earle's buffer and cell culture medium NCTC = 135), medium oxygen pressure (PO₂) (400 and 30 mmHg), and regional sampling of placental tissue (central, intermediate, and peripheral). All media contained glucose (1 g/L). The tissue (2-3 g/25 mL medium, pH 7.2-7.4) was incubated for 3 hours at 37C. ³H-inulin was used for the determination of the extracellular space.

Results: Incubation of both tissue forms yielded a higher metabolic activity as measured by glucose consumption and lactate production when incubated with Earle's buffer compared with incubations with NCTC medium. In general, the metabolic activity was consistently higher for small fragments compared with the large blocks. Extracellular space values found for large fragments (25-31%) were significantly lower than for small pieces (39-46%), indicating that an equilibration of the medium with the extracellular space is inadequate with large fragments. Incubation with small fragments showed that 1) there is a tendency for higher metabolic activity during incubation with lower PO₂, 2) the metabolically most active part of the placenta is the intermediate tissue region, and 3) placental metabolic activity was significantly higher at 28-33 weeks (n=5) than at term (n = 6). These differences were not seen with large fragment incubations.

Conclusion: The smaller tissue fragments are preferable for the in vitro incubation study of placental glucose metabolism. Apparently, there are differences in the metabolic activity with regard to the placental tissue region and gestational age.