Measurements of 3-O-methyl glucose (3-O-MG) transport were undertaken in order to determine whether a specific concentration of tryptophan stimulated glucose transport into peripheral tissues of the rat and might, thereby, prevent epinephrine-induced hyperglycemia. Transport studies were conducted using isolated tissues in vitro in Krebs-Ringer bicarbonate medium, pH 7.4, 37 °C, under gassing with 95 % oxygen: 5 % carbon dioxide. 3-O-Methyl glucose transport into the isolated hemidiaphragm and liver slice preparations of the rat was linear during the first 60 and 30 min, respectively, of incubation. Adding epinephrine (5.3 µM) to the preparations did not significantly alter the rate or extent of 3-O-MG transport into either preparation. Neither tryptophan (2.5 mM), epinephrine (5.3 µM), nor epinephrine plus tryptophan significantly affected 3-O-MG transport into hemidiaphragms in vitro. Additional transport studies were conducted in rats in vivo. 3-O-Methyl glucose and either epinephrine (1 mg/kg, s.c), tryptophan (2.5 mM/kg, i.p.), or epinephrine plus tryptophan were injected into rats. After 1 h, the animals were sacrificed, and the transport of 3-O-MG into the tissues was determined. None of the injections altered 3-O-MG concentration in serum or diaphragm in vivo. The injection of tryptophan decreased 3-O-MG concentration in heart (28 %, p < 0.001) and skeletal muscle (16 %, p < 0.05), but did not alter its concentration in serum, liver, or diaphragm. Injecting epinephrine increased 3-O-MG concentration in liver (p < 0.05), decreased it in skeletal muscle (22 %, p < 0.01), but did not change it in serum, heart, or diaphragm. The injection of epinephrine plus tryptophan increased 3-O-MG concentration in liver (p < 0.02), decreased it in skeletal muscle (p < 0.01), and did not alter the concentration in the other tissues. These results demonstrate that tryptophan does not increase glucose transport, but rather decreases it in some tissues.

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