The severity of diabetes is a major determinant of myocardial damage in the rat.

The severity of insulin-dependent diabetes mellitus had a marked effect upon the development of myocardial sequelae in the rat. Even with the same degree of hyperglycemia, glycosuria, polydipsia, and polyuria, moderately diabetic animals did not develop the degenerative ultrastructural changes seen in myocardium from more severely diabetic rats. These included decreased cardiocyte size, loss and disorganization of myofibrils, and loss of sarcoplasmic reticulum and transverse tubules. Since hyperglycemia and glycosuria are frequently used as the primary, and often sole, criteria for identifying diabetes in experimental animals, this study demonstrates the need to more specifically define the severity of the disease in studies of the heart.