SKELETAL-MUSCLE COLLAGEN TYPE-I AND TYPE-II MESSENGER-RNA, PROLYL 4-HYDROXYLASE, AND COLLAGEN IN HYPOBARIC TRAINED RATS

Skeletal muscle collagen expression was studied in normobaric sedentar y (NS) and training (NT) and hypobaric sedentary (HS) and training (HT ) rats after experimental periods of 10, 21, and 56 days. The weights of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles were increased between the experimental period of 21 and 56 da ys so that EDL weight was 57 (P < 0.01) and 36% (P < 0.05) higher in 5 6 days HS (56HS) and 56 days HT (56HT), respectively, than in 56 days NS (56NS). Soleus muscle weight was higher in 56HS (61%; P < 0.01) and in 56HT (27%; P < 0.05) than in 56NT. In EDL muscle, collagen type I mRNA level was lower in 56HT than in 56NS (36%; P < 0.05) and 56NT (44 %; P < 0.01). In 56HT, collagen type III mRNA level was 39 (P < 0.01) and 42% (P < 0.05) lower than in 56NS and 56HS, respectively. In soleu s muscle, prolyl 4-hydroxylase activity was greater (P < 0.05) in 56NT , 56HS, and 56HT than in 56NS. Total hydroxyproline content-in EDL mus cle was increased in 56HS and 56HT and in soleus muscle of 56HS. In co nclusion, although collagen types I and III mRNA levels in EDL muscle decreased in 56HT, the prolyl 4-hydroxylase data suggest unchanged syn thesis of total collagen. Exposure to hypobaric conditions as such, it s combination to endurance training, as well as training in normobaric conditions increased prolyl 4-hydroxylation capacity in soleus muscle , which may indicate respective change in collagen synthesis rate.