Abstract
The aerobic production of lactate from glucose by the intestine has been proposed as an important source of carbon substrate for liver glycogen synthesis. In order to determine the significance of aerobic and anaerobic lactate production by jejunal villus cells, we determined lactate production and energy charge (EC), an indicator of intracellular oxygen availability and oxidative phosphorylation activity, in jejunal villus cells under aerobic and anaerobic conditions. Adult rat villus cells were incubated in a polarographic chamber containing Krebs Ringer Phosphate Buffer, 5 mM glutamine, 5 mM glucose and 5 mg/ml BSA. The rate of O2 consumption was determined using a Clark electrode. Aliquots of assay mixture were removed and analyzed for lactate, ATP, ADP and AMP conc, after 5 periods (5 min (aerobic), 4 min (anaerobic-O2 sat<3%), 4 min anaerobic, 4 min recovery in which the cells were placed in an aerobic medium and a 4 min aerobic period). Lactate production was calculated by substracting lactate concentration of successive samples and dividing by the time interval. EC=(ATP+0.5*ADP)/(ATP+ADP+AMP). The results are means±SD (n=4). The rate of O2 consumption, initially 0.66±.05(μmol/mg/min) was not affected by 8 min of hypoxia(0.7±.23). The EC during the aerobic period was 0.60±.07. The EC decreased to 0.52±.08 and 0.46±.05 (p<.03) at the end of 4 and 8 min of hypoxia, indicating that the hypoxic conditions altered the enterocyte oxidative phosphorylation activity. After the recovery and subsequent aerobic period, the EC increased to 0.67±.07 and 0.65±.09 respectively, Indicating aerobic metabolism of undamaged enterocytes. Lactate production remained constant during the initial aerobic and anaerobic periods (45.8±2.0 nmol/mg/min, 30.8±9 and 37.0±0). During the recovery period when the EC was initially .46, lactate production increased to 77.8±20.1 (p<.01). In the subsequent aerobic period, lactate production decreased to its original rate (42.3± 13.1). In summary, under aerobic conditions with a high EC, enterocytes can metabolize glucose to lactate and is a possible source of portal venous lactate. Furthermore, enterocyte lactate production can increase two fold during hypoxic conditions.
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Kimura, R., Snow, K. & Ferretti, M. CHANGES IN LACTATE PRODUCTION IN ENTEROCYTES UNDER AEROBIC AND ANAEROBIC CONDITIONS. Pediatr Res 21 (Suppl 4), 343 (1987). https://doi.org/10.1203/00006450-198704010-01055
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DOI: https://doi.org/10.1203/00006450-198704010-01055