Microvascular remodelling after endurance training with Co2+ treatment in the rat diaphragm and hind-leg muscles

This study was designed to examine the changes in capillary geometry, especially the distribution of arteriolar and venular capillaries, in the skeletal muscles of female Wistar rats after endurance training with and without chronic CoCl(2) administration. Four groups of rats were used: non-treated sedentary, non-treated training, Co(2+)-treated sedentary, and Co(2+)-treated training. Exercise training by running lasted for 5 weeks at 25 m/min on a 20% gradient, 10-60 min/d, 5 d/week. The Co(2+)-treated rats drank water containing 0.01% CoCl(2) for 5 weeks. Morphological findings were obtained from the soleus (SOL), deep (PLd) and superficial (PLs) portions of plantaris, and diaphragm (DIA) muscles. Co(2+) administration significantly increased the blood hemoglobin concentration by approximately 25% with and without training. Only in DIA, the Co(2+) treatment alone significantly increased total capillary density and the capillary-to-fiber ratio (C : F) (p<0.05). Both training groups with and without Co(2+) administration showed a significant increase in the C : F in SOL and PLd (p<0.05). In PLd, the increase was significantly greater in the Co(2+)-treated training group than in the non-Co(2+)-treated training group (p<0.05). Training significantly increased the proportion of arteriolar capillaries while it decreased that of venular capillaries in both SOL and PLd (p<0.05). These changes were also observed in PLd after training with Co(2+). The densities of VEGF-positive and TGF-beta1-positive capillaries remained unchanged in all muscle portions examined after either Co(2+) administration or exercise training. These results suggest that chronic Co(2+) administration causes adaptive changes in the oxygen transport system in respiratory muscle and facilitates exercise-induced angiogenesis in hind-leg muscles.