Effects of dilated cardiomyopathy on the diaphragm in the Syrian hamster

This study aimed to elucidate changes in respiratory muscles and their mech anism in cardiomyopathy, The contractile properties and histology of the di aphragm, as well as serum levels of insulin-like growth factor (IGF)-1, wer e examined in 10 hamsters with idiopathic dilated cardiomyopathy (CM) and 1 0 controls. At 28 weeks, body weight in CM was reduced compared with controls (114+/-10 versus 144+/-14 g, p<0.0001), The ratio of diaphragm to body weight was si gnificantly higher in CM than in controls (0.228+/-0.015 versus 0.182+/-0.0 17, p<0.0001), Dt vitro, maximal diaphragmatic twitch (303+/-63 versus 455/-119 g.cm(-2)) and tetanic tensions (1,555+/-369 versus 2,204+/-506 g.cm(- 2)) were significantly lower in CM than in controls (p<0.005). The half-rel axation time was significantly shorter in CM(19+/-1 ms) than in controls (2 4+/-3 ms, p<0.0005), Fatiguability at 25 Hz was significantly less in CM (2 8%) than in controls (42%, p<0.0001), Diaphragm and gastrocnemius adenosine triphosphatase staining showed type I fibre atrophy in CM, associated with an increase in the number of type I fibres in the diaphragm, Histological examination of both muscles revealed an abnormal muscular pattern, Finally, serum levels of IGF-1 were 47% lower in the CM group than in controls (p<0 .0001) and were clearly related to the changes in the contractile propertie s and histology of the diaphragm, In conclusion, cardiomyopathy in hamsters: 1) depressed the force-generatin g capacity and shortened the relaxation of the hamster diaphragm; 2) induce d type I fibre atrophy in combination with a myopathic pattern; and 3) was associated with a significant reduction in serum levels of insulin-like gro wth factor-1, related to the diaphragmatic changes. Whether these changes a re primary myopathic or secondary to heart failure remains to be elucidated .