Detraining losses of skeletal muscle capillarization are associated with vascular endothelial growth factor protein expression in rats

The purposes of this study were as follows: (1) to examine basal vascular endothelial growth factor (VEGF) protein concentrations following 10 weeks of endurance training and after 7 days of detraining; and (2) to examine the acute VEGF protein response to a single 1 h exercise work bout in trained and detrained animals in relationship to changes in capillary indices following training and detraining. Thirty-three Sprague-Dawley rats were randomized into the following six groups: (1) control-basal; (2) control-acute exercise; (3) trained-basal; (4) trained-acute exercise; (5) detrained-basal; and (6) detrained-acute exercise. Groups 3-6 performed endurance training on a rodent treadmill three times per week for 10 weeks. Following the training intervention, rats in groups 5 and 6 remained cage confined (i.e. detrained) for 7 days. As expected, training increased soleus and plantaris muscle capillarity and attenuated the VEGF response to acute exercise. Seven days of detraining, however, resulted in a regression of capillary contacts and individual capillary-to-fibre ratio in the plantaris and soleus muscles compared with the trained group (P < 0.05). Restoration of the VEGF protein response to acute exercise was evident in both muscles, but only statistically significant in the plantaris muscle (P < 0.05). This is the first study to demonstrate the temporal relationship between VEGF protein expression and skeletal muscle capillarity within the first week of detraining. The findings of the present investigation are consistent with the hypothesis that reduced capillarity impairs oxygen availability to the working muscles. The results indicated that training-induced angiogenic remodelling was reversible following 1 week of detraining and may be modulated by VEGF.