Restoration of glycogen from lactic acid in the anaerobic swimming muscle of plaice, Pleuronectes platessa L.

The conclusion from two in vivo experiments is that a significant proportion of the lactic acid, normally formed by glycolysis from glycogen and held in the muscle cells following exhausting exercise of the anaerobic swimming muscle of the teleost fish Pleuronectes platessa L, is converted by gluconeogenesis to form glycogen in the recovering muscle.
In the first experiment a technique for measurement of ³H]glucose turnover in the plaice was developed and applied to measure turnover in resting and exhausted fish. It is concluded that insufficient glucose was moved through the circulation to account for the rate of glycogen formation observed in the recovering exhausted muscle.
In the second experiment, an intramuscular injection of ¹⁴C]lactate to exhausted fish revealed a direct uptake of ¹⁴C]lactate by the recovering muscle cells, and the incorporation of substantial proportions of lactate into the restored glycogen. Simultaneous use of ³H]-mannitol allowed measurement of the isotope distribution between extra- and intracellular spaces.