Histologic and ultrastructural studies on the myocardium in spontaneously diabetic KK mice: a new animal model of cardiomyopathy.

The hearts from spontaneously diabetic KK mice and control mice were examined by light and electron microscopy. Myocardial degeneration, myocardial fibrosis and calcium deposits in the myocardium were extensive in KK mice aged 8 weeks. In myocytes of newborn KK mice, an irregular arrangement of myofibrils and poorly formed Z bands were found. Ultrastructural changes in myocytes of KK mice aged 4 weeks consisted of destruction of mitochondria, degenerated myofibrils and abnormalities of Z bands. However, increased mucopolysaccharides in interstitium and thickened basement membranes of capillaries were not found in KK mice, in contrast to the previous reports of myocardial changes in diabetic C57BL/KsJ mice, alloxan-diabetic dogs and hypertensive-diabetic rats. These observations suggest that the cardiomyopathy found in KK mice is not secondary to diabetes mellitus but is caused by other factors. In conclusion, myocardial ultrastructural abnormalities are present in newborn KK mice. Thus, this animal can be used as a model of cardiomyopathy.