[Effect of x-ray irradiation on the activity of key enzymes in heme biosynthesis and breakdown in the rat liver].

The authors studied the effects of the whole-body x-irradiation on the activity of delta-aminolevulinate synthase and heme oxygenase in the liver of Wistar rats. The activity of delta-aminolevulinate synthase decreased to 81-49% of normal by the 1st-3d day after irradiation in a dose of 7 Gy followed by partial normalization of the enzyme activity by the 5th-7th day. The activity of heme oxygenase was over 2 times as increased by the 5th-7th day following irradiation in a dose of 7 Gy. Irradiation in a dose of 5 Gy did not alter the activity of heme oxygenase and caused a negligible reduction in the activity of delta-aminolevulinate synthase. During the most pronounced decrease in the rate of heme synthesis in the liver of irradiated rats, there was an elevation in the level of "free" heme (measured by the degree of tryptophane pyrrolase saturation with heme). This attests to a possible lowering of the rate of heme utilization in the synthesis of heme. A possible role of the effects described in the irradiation-induced decrease in the content of cytochrome P-450 in the animals' liver.