X-irradiation results in a reduction in histidine decarboxylase activity of the glandular stomach of the rat. In nonirradiated animals, force feeding stimulates histidine decarboxylase activity about 4-fold in 3 hours but, in x-irradiated animals, this response is reduced by over 70%. In contrast, an injection of pentagastrin or insulin 24 hours after exposure to x-irradiation (2000 rads) produces a rise in histidine decarboxylase activity of the glandular stomach which is similar in magnitude to that obtained in nonirradiated animals. This increase in enzyme activity is prevented by cycloheximide but not by actinomycin D suggesting that synthesis of new messenger RNA may not be obligatory in the response of this enzyme system. The failure of food to stimulate histidine decarboxylase activity in starved, x-irradiated animals suggests that x-irradiation exerts an effect prior to the vagal release of endogenous gastrin.

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