Blood Metabolites After Intestinal Absorption of Amino Acids in Locusts

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Abstract
1. After infusion of the locust gut with L-glutamate-U-14C, L-glutamine was found to be the major radioactive product in blood sampled 1 h later. Smaller amounts of alanine were also found. In most experiments not even traces of unchanged L-glutamate were detectable. 2. When D-glutamate was infused, the main radioactive product was D-glutamate, with lesser amounts of glutamine. With L-alanine-1-14C, the major product was unchanged alanine, with smaller amounts of glutamine. With glycine-1-14C, only glycine could be recovered. 3. Gastric caeca, which presumably are the major tissue sites of amino acid absorption, metabolized L-glutamate to glutamine and alanine. Metabolism of glycine was negligible. 4. Slow infusion of L-glutamate-1-14C into the haemocoel of locusts was followed by recovery of the radioactivity from blood as glutamine. Unchanged L-glutamate was not in evidence. 5. Rises in the blood concentration of L-glutamate appear to be suppressed. This seems not to be the case for D-glutamate, L-alanine, and glycine. 6. Destruction of dietary L-glutamate in the gut wall may be a functional adaptation to help maintain a low blood concentration of the pharmacologically active substance while producing energy required for absorption and tissue maintenance. Should any L-glutamate enter the blood from the gut or other tissue source, it will be converted to glutamine, which suggests the existence of a complementary mechanism for ensuring low blood L-glutamate.