Effects Of Progressive Hypoxia On Ultrastructure Of Myocardial Capillary In Training Rats

Introduction
Angiogenesis occurs during muscle remodeling after hypoxic training, which leads to a decrease in the diffusing
distance for oxygen, and hence an improvement to hypoxic resistance. However, it is not yet well known how
incremental hypoxia affects angiogenesis in myocardium during training. Therefore, in this study, progressive hypoxia
was administrated to determine ultrastructural changes of myocardial capillariy in training rats.

Methods
40 male SD rats were randomly devided into 5 groups: control (Ⅰgroup), normoxic training (Ⅱ group), exposed to
hypoxia for 3h after every normoxic training (Ⅲ group), hypoxic training (Ⅳ group), exposed to hypoxia for 3h after
every hypoxic training (Ⅴgroup). 8 weeks Progressive treadmill training (from 15m/min for 25min in the first week to
28 m/min for 50min in the last week, the treadmill degree kept at 10%) and incremental hypoxia (from 18.2 kPa to 15.2
kPa, respectively) were applied. 3 samples from left ventricles of heart each group were fixed and dehydrated, and
sections were viewed in a transmission electron microscope (Hitahi H-800).

Results
Although the number of capillary did not increased evidently in Ⅱ group and Ⅲ group compared with the control, it
increased markedly in Ⅳ group, especially in Ⅴgroup. There was no morphological evidence of endothelial cell
damage, such as swollen nuclear and pale cytoplasm. There were some ultrastructural changes of angiogenesis in Ⅳ
group and Ⅴgroup (Fig.1., B and C).

Discussion/ Conclusions
Current evidence suggests that training in hypoxia is superior to training of the same intensity in normoxia for
myocardial capillary angiogenesis. Morphological changes with irregular luminal providing a high surfuce/volume ratio
can enlarge the area for oxgen exchange, which is benefit to hypoxia resistance during exercise.

References
[1]. Egginton S. & Gerritsen M. (2003). Microcirculation, 10, 45-61.
[2]. Haas T. L. , et al. (2000). Am J Physiol Heart Circ Physiol, 279, H1540-H1547.

NOTA: O texto com a iconografia está no anexo.

Arquivo