Despite remarkable advances in
therapy,
heart failure remains a leading cause of morbidity and mortality. Although enhanced
beta-adrenergic receptor stimulation is part of normal physiologic adaptation to either the increase in physiologic demand or decrease in cardiac function, chronic beta-
adrenergic stimulation has been associated with increased mortality and morbidity in both animal models and humans. For example, overexpression of cardiac Gsalpha or
beta-adrenergic receptors in transgenic mice results in enhanced cardiac function in young animals, but with prolonged overstimulation of this pathway,
cardiomyopathy develops in these mice as they age. Similarly, chronic
sympathomimetic amine therapy increases morbidity and mortality in patients with
heart failure. Conversely, the use of beta-blockade has proven to be of benefit and is currently part of the standard of care for
heart failure. It is conceivable that interrupting distal mechanisms in the
beta-adrenergic receptor-
G protein-
adenylyl cyclase pathway may also provide targets for future therapeutic modalities for
heart failure. Interestingly, there are two major
isoforms of
adenylyl cyclase (AC) in the heart (type 5 and type 6), which may exert opposite effects on the heart, i.e., cardiac overexpression of AC6 appears to be protective, whereas disruption of type 5 AC prolongs longevity and protects against cardiac stress. The goal of this review is to summarize the paradigm shift in the treatment of
heart failure over the past 50 years from administering
sympathomimetic amine agonists to administering
beta-adrenergic receptor antagonists, and to explore the basis for a novel
therapy of inhibiting type 5 AC.