Limited Permeability and Metabolism of L-Glutamate in the Locust Gut Wall

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Abstract
1. A method is described which enables the passage of nutrients through the gut wall of locusts to be studied quantitatively in vivo. The method consists of infusing the radio-labelled precursor into the gut lumen while the haemocoel is perfused with saline. The perfusate is collected and analysed. 2. Compared to L-alanine and glycine, intact L-glutamate crosses the locust gut wall slowly, if at all. 3. Metabolism of L-glutamate in the gut wall is extensive, that of alanine markedly less, while there is little metabolism of glycine. 4. It is suggested that limited permeability and extensive metabolism in the gut wall combined to severely restrict the entry of intact dietary L-glutamate into the blood. 5. The gut wall may be an important site of regulation of blood L-glutamate, preventing or hindering influx of this abundant dietary amino acid. The system could be a contributing factor in protecting neuromuscular synapses from non-adaptive excitation by helping to prevent the concentration of blood L-glutamate from rising.