Contractile properties of soleus muscles isolated from 31 euthyroid (EU), 20 @entity1378 ( @entity1378 ), and 18 myxedematous (MY) @entity35 were studied in a myograph. At 100 stimuli/sec maximum isometric tension was essentially identical in EU (17.2 +/-0.5 g/mm(2)) and @entity1378 (17.7 +/-0.5 g/mm(2)) muscles, but was significantly depressed in MY muscles (11.5 +/-0.7 g/mm(2)). The rate of tension development was increased in @entity1378 (103 +/-4.5 g/sec per mm(2)) as compared to both EU (86.2 +/-4.6 g/sec per mm(2)) and MY (38.4 +/-2.2 g/sec per mm(2)) muscles, while the duration of the active state was shortened in @entity1378 (77.1 +/-2.3 msec) as compared to EU (105.1 +/-1.1 msec) muscles and was prolonged in MY muscles (153.3 +/-6.0 msec). The mean rate of isometric relaxation was 26.5 +/-4.9 g/mm(2) per sec in EU muscles, more rapid in @entity1378 muscles (33.1 +/-1.3 g/sec per mm(2)), and slower in MY muscles (16.0 +/- g/mm(2) per sec). The fusion frequency was greater in @entity1378 muscles, averaging 68.5 +/-3.6 stimuli/sec compared to EU muscles (38.1 +/-1.2 stimuli/sec) and to MY muscles (33.3 +/-4.0 stimuli/sec). At 40 stimuli/sec tension averaged 16.4 +/-0.8 g/mm(2) in EU muscles while at the same frequency tension was reduced in @entity1378 muscle, averaging 14.2 +/-0.5 g/mm(2). All differences were significant (P < 0.01). In conclusion, @entity1378 and MY result in profound alterations in the intrinsic contractile properties of skeletal muscle. While tension in @entity1378 muscles is maintained in vitro at a stimulus frequency of 100 stimuli/sec, the reduction in duration of active state may lower tension in vivo by preventing complete fusion of contractile events. In MY tension is reduced as a consequence of the lowered intensity of the active state. These changes explain, at least in part, the weakness of @entity121 in both @entity1378 and MY.

Effect of alterations in the thyroid state on the intrinsic contractile properties of isolated XXXX skeletal muscle.

@entity35 :: ('10116', 'Species') :: ['rats'] @entity121 :: ('MESH:D009135', 'Disease') :: ['muscle activity'] @entity1378 :: ('MESH:D006980', 'Disease') :: ['HT', 'hyperthyroid']
@entity35 :: (10116,Species) :: ['rat']
