Iron Distribution in Different Tissues in Rats Following Exercise

Abstract

Iron plays an essential role in blood oxygen transport and in muscle physiology. No conclusive data exist in the literature concerning its tissue distribution and behavior following exercise and training. The aim of the present work was to analyze the Fe content in different tissues following a single session of swimming to exhaustion and after swimming training in rats in order to more extensively describe the changes of Fe distribution provoked by exercise. Animals were divided into four groups (n=10): control group at rest, trained group at rest, control group after exercise, and trained group after exercise. First, rats swam until exhaustion and the maximal swimming time was noted. The training protocol consisted of swimming (5 d/week for 3 wk), limiting the time to 60% of the maximum obtained during the first session to exhaustion of each rat. The variables measured were erythrocytes, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and, Fe in liver, kidney, erythrocytes, heart, muscle, bone, and serum. Variations in plasma volume were also calculated. Tissues presented two different profiles with regard to the changes of Fe concentration provoked by training: those displaying higher values of Fe after training, such as liver, heart, muscle, and serum, and those displaying lower values, such as bone, kidney, and red blood cells. These changes in the distribution of Fe in different tissues could be the result of an increase in the needs and use of Fe, shown by active tissues at exercise, and it is possible that the hormonal changes provoked by stress lead to a different behavior of Fe proteins.

Changes of Iron Stores and Duodenal Transepithelial Iron Transfer During Regular Exercise in Rats

“…Taking into account that at the end of exercise the rats in the three different exercise groups were all at varying developmental stages and had their different exercise duration, we propose that the effects of regular exercise, along with a high dietary iron content, on liver iron stores and duodenal iron absorption depend on individual body development/ growth in growing rats. This may explain the conflicting results on liver iron levels in exercised rats in previous studies [13][14][15][16], in which the rats displayed different levels of development. However, it should be noted that our study did not separate the effects of the duration of exercise training from the timing of exercise training within the rat's life cycle.…”

“…Two human studies, using radio-iron labeling methods, showed that exercise decreased or increased the feces iron content in athletes with prelatent ID or low serum ferritin, respectively [23,24], while a third report [25], using a stable isotope iron technique, showed a decrease in iron absorption during exercise rather than a resting period in juvenile athletes. In both rat studies [12,16], the fecal radio-iron activity increased and decreased, respectively. Therefore, our study was designed to determine if regular exercise affects iron absorption and the mechanism for these effects, by examining 59 Fe transfer kinetics in the isolated duodenal segments of rats.…”

“…The swimming exercise was a modification of the Ruckman and Sherman method [16], as described in our previous studies [18,27]. Briefly, the rats in the exercise groups swam in a glass swimming basin with a water depth of 50 cm and temperature of 35±1°C.…”

“…To date, regular exercise has been suggested to decrease [12,13], increase [14][15][16], or have no effect [17] on body iron stores. Factors responsible for these conflicting results may include differences in experimental models, control of dietary iron, exercise length and intensity, and methods used in studies.…”

“…There are several relevant studies, including three human studies [23][24][25] and two studies of rats with diets containing adequate iron content [12,16], but their findings remain very controversial. Two human studies, using radio-iron labeling methods, showed that exercise decreased or increased the feces iron content in athletes with prelatent ID or low serum ferritin, respectively [23,24], while a third report [25], using a stable isotope iron technique, showed a decrease in iron absorption during exercise rather than a resting period in juvenile athletes.…”