| Iron is very important in improving athletes performance. Oxygen transport and the ability of aerobic oxidation and the production of ATP in mitochondria were affected by iron level. Iron deficiency affects the function of circulation system and skeleton muscle, and even leads to iron-deficient anemia. Sports anemia especially the iron-deficient anemia is an important problem in sports medicine. Although many people have done some researches on its mechanism, the molecular mechanism of iron status changed in exercise is not well determined. The discovery of DMT1 (divalent metal transporter 1), FP1 (ferroportinl), TfR (transferrin "receptor) and hepcidin may help to clearly illuminate the route of iron absorption, iron transport and metabolism. Some researches reported NO may play an important role in iron redistribution in exercise, while the molecular regulatory mechanism was unclear. Most of previous studies were focused on athletes' sports anemia after strenuous training, effects of different intensity training on the molecular mechanism of iron homeostasis is absent. Therefore, it is necessary to illuminate the regulatory mechanism of iron metabolism in different intensity exercise. The present study investigated the effects of different intensity swim training on serum iron status, iron distribution, the level of NO and the activity of NOS in serum and gastrocnemius, iron storage and utilization in rats' gastrocnemius and iron absorption in duodenal epithelium.60 female SD rats (90~100g) were randomly divided into three groups: control group (remained sedentary, CG), moderately exercised group (swam1.5h/day, MG) and strenuously exercised group (swam with different loads increased with week from 3% to 10% body weight, and with different periods increased with day from 90 min to 120 min, SG). The rats were sampled after 5 and 10-week swimming. The serum iron (SI), serum unsaturated iron-binding capacity (UIBC), total iron-binding capacity (TIBC), transferrin saturation (TS), Hematocrit, Hb, nitric oxide (NO) and nitric oxide synthase (NOS) in serum were identified. The non-heam iron of heart, liver, spleen, duodenum, gastrocnemius and bone marrow were measured after 5-week and 10-week swimming. Serum ferritin was mensurated using the enzyme linked immunosorbent assay (ELISA). The expression of TfR1, DMT1 and FP1 was detected by Western Blot. The expression of hepcidin mRNA in liver was examined by Reverse Transcription- Polymerase Chain Reaction (RT-PCR).The results were as follows:(1) The body weight of SG was significantly decreased compared with that of CG andMG during 8 to 10-week training (PO.01). At the end of 5-week swimming, Hct and RBC of MG and SG were significantly increased compared with that of CG (PO.01), and Hb of MG was higher than that of CG (PO.05). At the end of 10-week swimming, the RBC, Hb and Hct of MG were still significantly higher than that of CG. However, RBC, Hb and Hct in SG were decreased compared with that of MG (P<0.01).(2) The assessment of serum iron status showed: Compared to CG, the TS of MG and SG was improved after 5-week training, and UIBC of MG was decreased (P<0.05). The SI, TS and SF of MG were significantly increased compared with that of SG and CG (PO.01). The SI and SF of SG were lower than that of CG (P<0.05).(3) Non-heam iron distribution in different tissues: there was no difference observed in these three groups after 5-week training period. At the end of 10-week training, the non-heam iron in gastrocnemius of MG and SG were significantly increased than that of CG, while the non-heam iron in bone marrow of MG and SG was decreased (PO.01). The non-heam iron in cardiac muscle and bone marrow of MG were higher than that of SG(4) Immunohistochemical results showed that TfRl, DMTl and FP1 were membrane protein, and mostly expressed on the membrane of gastrocnemius. Western blot analysis showed the expressions of DMTl (IRE) and TfRl in MG and SG were higher than that of CG (P<0.05).The expression of DMTl (non-IRE) wasn't changed in MG and SG. FP1 in MG was decreased compared with that of CG (P<0.05).(5) The measurement of NO and NOS in serum and gastrocnemius showed: Both NO level and NOS activity in serum and gastrocnemius of MG were significantly increased compared with that of CG (PO.05). NOS and NO in serum of SG were higher than that of CG, however, NO in gastrocnemius of SG was lower than that of MG (PO.01).(6) DMTl staining seemed to be most intense in the luminal half of the epithelium, little in the basal side of epithelium and was nearly absent in mucus-secreting goblet cells. FP1 was mostly on the epithelium basolateral surface. Western blot analysis showed the expression of DMTl (IRE) and FP1 was significantly increased in MG compared with that of CG (PO.05). In contrast, there was no significant change of DMTl and FP1 level in SG. Furthermore, DMTl (non-IRE) level was not altered either in MG nor SG.(7) Quantification of liver hepcidin transcripts by RT-PCR showed: the expression of hepcidin mRNA in MG was significantly lower than that of CG. However, there was no significant difference in hepcidin mRNA expression between SG and CG.
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