Alterations of cardiac sympathetic neurotransmitter activity in congestive heart failure

The sympathetic nervous system exerts an important direct effect on cardiac function which is mediated by the release at the terminal sympathetic nerve endings of the neurotransmitter norepinephrine. These nerve terminals are complex structures involved in synthesis, uptake, binding and storage as well as release of norepinephrine. The evidence for alteration of many of these functions in congestive heart failure, which is characterized by a depletion of myocardial norepinephrine stores, is reviewed. Although cardiac norepinephrine depletion alone is not responsible for the intrinsic depression of cardiac contractility in failing heart muscle, this depletion probably removes a potentially important compensatory mechanism for augmenting myocardial force development and velocity of contraction in the failing heart. Evidence for parasympathetic-sympathetic system interactions as they affect the heart, as well as alterations in the parasympathetic nervous system in heart failure, is also presented briefly.