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The Anrep effect: an intrinsic myocardial mechanism
C G Nichols1, D A Hanck, B R Jewell
1Department of Physiology, University of Leeds, United Kingdom.
Canadian Journal of Physiology and Pharmacology
|July 1, 1988
Summary
Increasing afterload in cat heart muscles causes a biphasic contractility change. Initial decrease (antihomeometric) is followed by a slow increase (homeometric autoregulation), linked to diastolic length.
Area of Science:
- Cardiovascular Physiology
- Cardiac Muscle Mechanics
Background:
- Cardiac muscle contractility is influenced by loading conditions.
- Autoregulation mechanisms are crucial for maintaining cardiac output under stress.
Purpose of the Study:
- To investigate the biphasic response of cat papillary muscle contractility to increased afterload.
- To elucidate the mechanisms underlying antihomeometric and homeometric autoregulation.
Main Methods:
- Isolated cat papillary muscles were subjected to controlled increases in afterload.
- Contractility was assessed by measuring peak shortening, peak developed force, and peak dF/dt.
- Experiments were conducted at physiological temperatures (30°C and 37°C).
Main Results:
- Increased afterload induced an initial decrease in contractility (antihomeometric autoregulation).
- A secondary, slow increase in contractility (homeometric autoregulation) was observed, with faster kinetics at higher temperatures.
- Antihomeometric response was attributed to decreased active shortening, while homeometric response correlated with increased mean diastolic length.
Conclusions:
- Cat papillary muscles exhibit a biphasic contractility response to afterload increase.
- The findings suggest that increased diastolic length contributes to homeometric autoregulation (Anrep effect) in the whole heart.
- This study provides insights into the intrinsic mechanisms of cardiac adaptation to altered mechanical loads.