| Popis: |
It is generally acknowledged that training results in capillary growth in skeletal muscle, with the extent of growth varying according to length and type of training. There is also growth of arterioles and expansion of the whole vascular bed, as indicated by increased maximal conductance. Surprisingly, in the heart, training results in capillary growth almost predominantly in young animals, while growth of arterioles and enlargement of large vessels occurs in adults, even when not accompanied by capillary growth (see Hudlicka et al. 1992). There is no doubt that the changes in capillary supply are due at least in part to growth of endothelial cells, which was demonstrated by [3H]thymidine incorporation in capillary nuclei in the hearts of animals trained by swimming (Man-dache et al. 1973). Although there is no parallel evidence in skeletal muscles, increased capillarization demonstrated either by histochemical techniques which depict specifically capillary endothelium, or by electron microscopy, thus revealing all anatomically present vessels, are the result of growth of new vessels. |
