Myosin heavy chain of immature soleus muscle grafts adapts to
hyperthyroidism more than to elements of physical activity.
Devor, Steven T., and Timothy P. White.
Department of Human Biodynamics, University of California,
Berkeley, Berkeley, CA 94720-4480
APStracts 2:0462A, 1995.
The interaction of hyperthyroidism and the elements of physical
activity on early regeneration of muscle grafts was investigated.
Soleus (SOL) muscle grafts were studied 15-days following graft
operations in eu- and hyperthyroid rats. Hypotheses were tested
regarding the adaptation of the myosin heavy chain (MHC) profile of
grafts and non-grafted control muscles, and whether the effect of
hyperthyroidism would predominate over the opposing influence of
recruitment and mechanical load on MHC of grafts. Denervation and
myectomy of synergist muscles were employed to manipulate the
elements of physical activity. Denervation decreased the expression
of type I MHC, and hyperthyroidism furthered the shift toward a
"fast" isoform profile.or example, in denervated grafts type
IIb was undetected in euthyroid rats, and accounted for 31% of MHC in
hyperthyroid rats. Compared with control muscles, grafts in the
denervated and innervated-normal load groups demonstrated greater
plasticity, as the adaptive response of MHC to thyroid status was
more pronounced. Hyperthyroidism predominated over the opposing
influence of the elements of physical activity on the regulation of
MHC expression in innervated plus overload grafts. For example, type
I MHC was 86% of MHC profile of innervated plus overload grafts in
euthyroid rats, and only 49% in hyperthyroid rats. In conclusion, a
heightened plasticity for grafts was evidenced in denervated and
innervated tissues, and the regulation of MHC by thyroid hormone
predominated over that due to the elements of physical activity.
Received 24 February 1995; accepted in final form 11 October
1995.
APS Manuscript Number A218-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95