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1.
Two boys born in September 1949 played on uranium mill tailings from about ages 8 to 12. One of these boys was diagnosed as having leukemia at age 15.5. The 226Ra body burden of the survivor was measured at age 38. The whole-body 226Ra content measured by counting in vivo was 0 +/- 17 Bq and independently by Rn breath analysis as 4.3 +/- 2.1 Bq. At the same time, a control subject with no known exposure to 226Ra, matched in age, height, and weight, was also measured. The whole-body content was estimated as 4 +/- 15 Bq and independently by Rn breath analysis as 5.5 +/- 3.7 Bq. The body burden of the control subject was not significantly different from that of the exposed person. The radiation dose to the marrow-free skeleton assuming a constant 226Ra:Ca ratio since birth was 0.49 and 1.33 mGy at ages 14 and 38, respectively. The radiation dose to the marrow-free skeleton assuming 226Ra intake only between ages 8 to 12 was 1.4 and 2.8 mGy at ages 14 and 38, respectively. The best estimate is the mean of these two estimates: 0.9 and 2.1 mGy at ages 14 and 38, respectively. The alpha-particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. Since no excess was found for the radium dial painters whose doses were much higher, the induction of leukemia by doses of this magnitude would seem quite unlikely. 相似文献
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Age-related changes in lung collagen metabolism. A role for degradation in regulating lung collagen production 总被引:3,自引:0,他引:3
Lung collagen levels are determined by a balance between synthesis and degradation, processes known to have rapid rates in young animals. Here, we report age-related changes in lung collagen synthesis and degradation in rats at five ages from 1 month to 2 yr. Synthesis rates were determined after injection of [14C]proline with a flooding dose of unlabeled proline, and its appearance as hydroxy-[14C]proline in protein. To determine degradation of newly synthesized collagen, the appearance of hydroxy-[14C]proline, either free or in low-molecular-weight peptides, was compared with hydroxy-[14C]proline in protein. Fractional collagen synthesis rates decreased from 13.51 +/- 0.54%/day at 1 month to 0.97 +/- 0.14%/day at 2 yr of age (p less than 0.05). Total lung collagen production also fell, but only after 15 months, when it decreased from 2.01 +/- 0.16 mg/day at 15 months to 0.54 +/- 0.10 mg/day at 2 yr of age (p less than 0.05). Fractional rates of total collagen degradation, calculated from the difference between rates of synthesis and rates of collagen deposition, decreased 20-fold from 1 month to 2 yr of age. The proportion of newly synthesized collagen degraded increased from 27.6 +/- 3.2% at 1 month to a maximum of 82.3 +/- 1.1% at 15 months. These results suggest that lung collagen synthesis and degradation occur throughout life, and that degradative pathways may play important roles in regulating collagen production during growth and ageing. 相似文献
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