Effect of different durations of exercise on transferrin-bound iron uptake by rat erythroblast

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This study evaluated effects of different durations of exercise on transferrin receptor (TfR) expression on the membrane of rat erythroblasts. Female rats were assigned to six groups: 3, 6 and 12 months of strenuous exercise (swimming 2 h/day, 5 days/wk) groups and their corresponding controls. At the end of experiments, the erythroblasts were isolated for Tf binding assay and transferrin-bound iron (Tf-Fe) uptake. Tissue non-heme iron and hematological iron indices were also measured. The TfR number on the cells was about 603,189 ± 107,562, 890,150 ± 164,849 and 384,695 ± 46,295 molecules/cell in three control groups (3, 6, 12 months) respectively. Exercise groups had significantly higher levels of TfR than those of the control groups, being 1,374,137 ± 243,677, 2,175,360 ± 462,737 and 1,012,759 ± 249,423 molecules/cell in 3, 6 and 12 months of exercise groups respectively (p < 0.05). After 30 min of incubation, cellular Tf approached to levels of 8.28 ± 1.94, 10.73 ± 3.30 and 6.60 ± 0.93 fmole/10 6 cells in 3, 6 and 12 months of exercise groups, while the corresponding control values were 3.09 ± 0.36, 5.03 ± 1.01 and 2.51 ± 0.88 fmole/10 6 cells respectively (all P < 0.05). The rates of cellular iron accumulation were 7.07 (3), 8.79 (6) and 5.96 (12 month) fmole/10 6 cells/min in the exercised rats and 2.91, 3.85, and 2.03 fmole/10 6 cells/min in their corresponding controls (all p < 0.05). However, no significant difference was observed in the ratios (Exercise/Corresponding control) of the increased TfR expression, Tf-Fe uptake and Tf endocytosis as well as of the decreased plasma iron and tissue non-heme iron levels induced by different periods of exercise. Furthermore, the increase in the length of exercise (6 or 12 month) did not induce a remarkable decrease in plasma hemoglobin and hematocrit. These results indicate that a true iron deficiency or ‘sport anemia’ can not develop even if under longer periods (6 or 12 month) of strenuous exercise.