Histochemical characteristics of soleus muscle in hGH transgenic mice.

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.