Abstract
Abstract
Histochemical characteristics of soleus muscle were compared in human growth hormone (hGH) transgenic mice vs their nontransgenic littermates. Plasma of transgenic mice contained hGH (7.1 ± 0.7 and 6.7 ± 0.4 ng/ml, mean ± SE, at 5 and 11 months of age, respectively); hGH was not detectable in plasma of nontransgenic littermates. Body and soleus weights were greater (approximately 55 and 25%, respectively) and both type I and type IIA fibers were larger in transgenic animals. Most significantly, fiber type composition of the soleus muscle was different in hGH-transgenic animals, i.e., the percentage of type I fibers was significantly greater than in nontransgenic mice (77.2 ± 5.1% vs 58.4 ± 2.5%). It is generally believed that skeletal muscle fiber composition is determined predominantly by neural influences (1, 2). These data suggest hormonal factors, growth hormone, also affect the phenotype of skeletal muscle myosin.
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