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  • Title: L-tryptophan inhibition of epinephrine-stimulated phosphorylase activity in vivo and in vitro.
    Author: Sanders RB, Sagur V.
    Journal: Pharmacology; 1978; 16(6):321-32. PubMed ID: 209483.
    Abstract:
    The administration of L-tryptophan prevented the normal rise in blood sugar concentration that usually follows the injection of epinephrine into rats. Of the several possible mechanisms by which tryptophan could inhibit epinephrine-induced hyperglycemia, one might be that tryptophan prevented the activation of the enzyme, phosphorylase, which is an indirect result of epinephrine action on the liver. This report presents evidence supporting this hypothesis: (1) The injection of tryptophan (2.5 mM/kg) prevented epinephrine-induced glycogenolysis in the liver of rats by 100%. (2) The time courses of epinephrine-induced hyperglycemia and activation of phosphorylase in liver were nearly identical. (3) The injection of tryptophan completely inhibited (100%) the epinephrine-induced phosphorylase activation. (4) The addition of tryptophan in vitro completely inhibited (100%) the epinephrine-induced activation of phosphorylase. (5) Tryptophan inhibition of epinephrine-induced hyperglycemia occurs immediately after tryptophan administration. (6) The addition of cyclic AMP blocked the tryptophan inhibition of epinephrine-induced phosphorylase activation. This evidence suggests that tryptophan may inhibit epinephrine-induced hyperglycemia in rats by preventing the activation of liver phosphorylase.
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