Myocardial contractility, lusitropy and calcium responsiveness in young (50 days) and hypertrophied (180 days) cardiomyopathic hamsters.

Contractility, lusitropy and responsiveness to the increase of external Ca2+ concentration were studied in left ventricular papillary muscles of normal and cardiomyopathic Syrian hamsters (SCH) from the UM-X 7.1 strain, both at the onset of myolysis (50-day-old animals) and at the cardiac hypertrophy stage (180-day-old animals) in the absence of congestive heart failure. A marked decrease in all indices of systolic performance was observed in 180-day-old myopathic hamsters as compared to age-matched controls. This was associated with (1) an impairment of the relaxation phase, (2) a loss of the load sensitivity of relaxation, and (3) a decrease in the inotropic and lusitropic responsiveness to Ca2+. On the other hand, when some indices of contraction and the inotropic response to Ca2+ were impaired in 50-day-old myopathic hamsters as compared to age-matched controls, relaxation phase and the lusitropic response to Ca2+ did not alter. This study shows that, in the UM-X 7.1 myopathic hamsters at the earlier stage of the disease, alterations in calcium homeostasis and contraction seem to be the first determinant factors of the development of heart failure when relaxation is not impaired. Conversely, when cardiac hypertrophy has developed, impaired relaxation may worsen heart failure.