Glucose uptake from, and lactate release into, the blood have been analysed in the active gas- depositing swimbladder of the immobilized European eel Anguilla anguilla. Under normoxic conditions, 0.72 micromole min-1 glucose was removed from the blood supply, while lactate was released into it at a rate of 1.16 micromole min-1. The rate of gas deposition into the swimbladder was significantly correlated with the rate of lactate production. Under hypoxic conditions, glucose consumption by, and lactate production of, the swimbladder tissue were reduced, as was the rate of gas deposition. Compared with normoxic conditions, lactate concentration in the swimbladder tissue was elevated after 1 h of hypoxia, indicating a decrease in lactate release. No difference in the osmolality of arterial and venous blood could be detected in these experiments. Combining the data for glucose uptake and lactate release measured under normoxic conditions with the values for O2 uptake and CO2 production of the swimbladder tissue measured under similar conditions in a previous study, a quantitative evaluation of glucose catabolism was performed. According to the O2 uptake of the tissue, only about 1 % of the glucose was oxidized, while about 80 % was fermented to lactic acid. The remaining 0.14 micromole min-1 glucose was presumably catabolized through the pentose phosphate shunt, as indicated by the CO2 production of 0.16 micromole min-1 that cannot be explained by aerobic metabolism.

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