Reticulocyte and micronucleated reticulocyte responses to gamma irradiation: effect of age.
The effect of age on the formation of radiation-induced micronucleated reticulocytes (MN-RETs) and reticulocytes (RETs) was investigated by exposing female C57BL/6J mice to graded doses of gamma rays from a (137)Cs source. Age at time of irradiation was 6, 16, or 32 weeks, and doses ranged from 0.5 to 3 Gy. A flow cytometric technique based on anti-CD71 labeling was used to measure RET and MN-RET frequencies in blood specimens collected 43 h post-irradiation. Mean RET frequencies declined in a dose-dependent manner for each age group. There was only one significant difference among the ages, that is, %RETs were not significantly reduced in the oldest animals at 0.5 Gy, whereas this dose did have a significant effect on the other age groups. MN-RET data were more complex. Age was observed to influence the baseline frequency of MN-RET, with the oldest mice exhibiting a significantly higher mean value. Each group's %MN-RETs values increased up to 1 Gy, but past this dose the frequencies plateaued or decreased. Age was observed to influence micronucleus frequency, with older mice exhibiting higher mean MN-RET values, especially at the high doses where the response was saturated (2-3 Gy). We hypothesize that these dissimilar responses can largely be explained by an age-related down-regulation of apoptosis whereby younger animals eliminate damaged bone marrow erythroid precursors with a greater efficiency compared with aged mice.
Dertinger
Stephen D
SD
Litron Laboratories, Rochester, NY, USA. sdertinger@litronlabs.com
Bemis
Jeffrey C
JC
Phonethepswath
Souk
S
Tsai
Ying
Y
Nowak
Irena
I
Hyrien
Ollivier
O
Palis
James
J
Chen
Yuhchyau
Y
D000367:Age Factors; D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays; D051379:Mice; D008810:Mice, Inbred C57BL; D048629:Micronuclei, Chromosome-Defective / Q000528:radiation effects*; D015162:Micronucleus Tests; D012156:Reticulocytes / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*