Connective tissue of "fast" and "slow" skeletal muscle in rats--effects of endurance training.

The connective tissue of two skeletal muscles having different contractile properties was investigated in trained and untrained rats. The animals to be trained were put to run on a treadmill 5 days a week for 4 weeks. The "slow" m. soleus (MS) showed higher malate dehydrogenase activity but lower lactate dehydrogenase activity compared to the "fast" m. rectus femoris (MRF). When whole muscles were taken into account, the concentrations of both hydroxyproline and hexosamines were higher for MS compared to MRF. In the middle section of MS there were more hexosamines than in that of MRF, but no similar difference existed in hydroxyproline. The histochemical staining of collagen, however, suggested that there is also more internal collagen for MS as against MRF. It can be supposed that collagen of MRF and MS is differently distributed in different muscle connective tissue components. Compared to MS, the solubility of collagen was higher in MRF, whereas no significant difference between the muscles existed in the prolyl hydroxylase activity. The concentrations of hydroxyproline and hexosamines or the solubility of collagen were not affected by the training given, but the activity of prolyl hydroxylase was increased in MS suggesting that the metabolism of collagen may be accelerated by physical training.