Glucose utilization rate, steady-state

The steady-state maternal glucose utilization rate can be calculated for a normal maternal glucose concentration of 120 mg % from the rate at which glucose diffuses into the placental tissue at steady state. This is given by ... 

Since the brain utilizes energy almost exclusively from oxidative metabolism of glucose, brain metabolism has been studied by focusing on net oxygen and glucose uptake. Oxygen consumption was classically measured as the arteriovenous difference of 02 content. When a substance is exchanged between brain and blood, the difference between its steady state of delivery to brain in the arterial blood and removal in the venous blood must be equal to the net rate of its utilization or... 

Initially the reactor was fed at 92 mL/h (dilution rate of 0.29 Ir1) with P2 medium until there were visible signs of cell mass accumulation. It took about 5 d to accumulate cell mass and for the reactor to be productive. The flow rate was then increased to 100 mL/h, and the reactor was allowed to achieve a new steady state. At this stage, a control experiment was run and the reactor was fed with P2 medium. At this dilution rate (0.32 h1), the reactor produced 6.86 g/L of total ABE and 2.36 g/L of total acids (Table 1). This resulted in an ABE productivity of 2.19 g/(Lh) and a yield of 0.27. This productivity is manyfold higher than the productivity achieved in a batch reactor (0.38 g/[L h]) (10). Glucose utilization was 39.1% of that available in the feed (65.5 g/L). In these reactors, high productivity is achieved but at the expense of a low ABE concentration in the effluent as well as low sugar utilization. To improve sugar utilization, the reactor effluent should be recycled back to the reactor after ABE removal (11). 

Sampling. For steady-state experiments, glucose was added continuously to the maternal reservoir. The placenta was weighed before being placed in the artificial uterus, the rate of utilization of glucose by the placenta was then estimated, and the rate of glucose added was set approximately to the estimated rate of utilization. 

Under steady-state conditions the problem of glucose uptake in the tissue disappears, and the rate of metabolism is exactly the rate of utilization. No significant difference in the results was observed or expected when the fetal flow rate was changed since with steady-state conditions in the system there is no net transfer at the fetal surface. The utilization rate depends upon the steady-state maternal and fetal concentrations. This rate is constant for a considerable time. 

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