The Effect of Whole-Body X-Irradiation on the Enzymatic Activity of Several Rat Tissues toward Uridine, Uridylic Acid, Cytidine, and Cytidylic Acid

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Abstract
Rat pancreas, spleen, liver, and brain homogenates were assayed for their enzymatic activity toward uridine, uridylic acid, cytidine, and cytidylic acid, after graded doses (325 r to 1300 r) of whole-body X-irradiation. Markedly differing results were obtained for spleen when the enzymatic activity was expressed as moles of substrate hydrolyzed per mg wet weight, per mg dry weight, or per total organ. Calculated with respect to all 3 parameters, the uridylic acid dephosphorylase activity increased well above the control values for pancreas and liver, but decreased in the case of spleen. The specific activities of spleen uridine phosphorylase and cytidylic acid dephosphorylase increased above that of the controls; however, the total organ activity toward uridine decreased below normal, whereas that toward cytidylic acid was unaffected. All other activities tested remained normal. The significance of these results is discussed.