Myocardial lesions and the alteration of atrial granularity in dystrophic mice.

Atria from dystrophic and non-dystrophic mice were examined by light and electron microscopy. Particular attention was paid to the granularity of the specific atrial granules and the development of the Golgi apparatus. At the light microscopic level, both a decrease in number and degenerative changes were recognized in the atrial cardiocytes, which were intercalated by increased connective and adipose tissues. At the electron microscopic level, the dystrophic atrial cardiocytes showed a variety of degenerative changes and a decreased number of granules; the impaired development of the Golgi apparatuses were noticed. A quantitative analysis revealed that the number of the granules per unit area in dystrophic cardiocytes was significantly smaller in both the right and left atria, and that the relative area occupied by the Golgi fields of the dystrophic was significantly smaller in the right atrium than in non-dystrophic controls. These findings indicate that the synthesis of atrial natriuretic polypeptide (ANP) is inhibited in dystrophic mice. It is suggested that the water and electrolyte imbalance known in dystrophic cases can be accounted for by the impaired secretion of ANP in the heart.