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Normal cardiac myosin ATPase and mechanics in pressure overload with digitalis treatment
Insights
Digitalis treatment prevents the decline in cardiac muscle myosin ATPase activity and contractile function caused by chronic pressure overload in cats. This indicates digitalis preserves heart function under stress.
Area of Science:
- Cardiology
- Biochemistry
- Physiology
Background:
- Chronic pressure overload impairs cardiac function by depressing myosin ATPase activity.
- Digitalis administration can attenuate the decline in mechanical function during pressure overload.
Purpose of the Study:
- To investigate the effect of digitalis on cardiac muscle myosin ATPase activity in cats with pressure overload.
- To determine if digitalis maintains normal ATPase activity in parallel with mechanical function under chronic pressure overload.
Main Methods:
- Four groups of cats were studied: controls, pressure-overload hypertrophy with or without failure (HF), digitalis-treated (D), and digitalis-treated with pressure overload (DHF).
- Cardiac muscle myosin ATPase activity and papillary muscle isometric rate of force development were measured.
Main Results:
- Myosin ATPase activity was significantly depressed in HF compared to controls (P < 0.05).
- Digitalis treatment (D and DHF groups) did not significantly alter myosin ATPase activity compared to controls (P > 0.05).
- Papillary muscle force development was depressed in HF but not in D or DHF groups compared to controls.
Conclusions:
- The depression of cardiac myosin ATPase activity observed in heart failure due to pressure overload is prevented by concomitant digitalis administration.
- Digitalis preserves both myosin ATPase activity and contractile function in the setting of chronic pressure overload.
Abstract:
Cardiac muscle myosin ATPase activity is depressed and contractile function impaired when the heart is subjected to a chronic pressure overload. Administering digitalis in the presence of chronic pressure overload significantly attenuates the decline in mechanical function. The current study sought to determine if the cardiac muscle myosin ATPase activity of cats treated with digitalis in the presence of pressure overload remains normal in parallel with the mechanical function. Four groups of cats were studied: normal controls (C), animals with pressure-overload hypertrophy with or without failure (HF), normal cats that received treatment with digitalis (D), and animals that received digitalis prior to and together with pressure overload (DHF). Compared to C, the maximum myosin ATPase activity of HF was significantly (P less than 0.05) depressed, but the maximum ATPase activity of D and DHF was not altered significantly (P greater than 0.05) from C. In parallel with the enzyme maximum activity, the papillary muscle isometric rate of force development was significantly (P less than 0.005) depressed in HF compared to C; D and DHF were not significantly (P greater than 0.05) different from C. It is concluded that the depression of myosin ATPase observed in HF is not present when digitalis is administered concomitant with the pressure overload.