Inotropic agents may be classified according to their primary mechanism of action (Table 1), i. e. whether their action is dependent on or independent of cyclic adenosine monophosphate (cAMP) . The most important inotropic agents used clinically are cAMP-dependent: β-receptor agonists (e. g. epinephrine) and phosphodiesterase inhibitors (e. g. amrinone), which will be discussed in this chapter. Forskolin is a direct activator of adenylyl cyclase and therefore independent of the β-receptor. Dibutyryl cAMP is a cAMP analogue which directly stimulates calcium ingress. Both these agents are investigational and useful in defining mechanisms of inotropic action. Digoxin, which inhibits the cellular sodium-potassium pump, and calcium, the “third messenger” in all muscle contraction, act independently of cAMP. However, their usefulness as IV inotropic agents is limited by their toxic effects. Alpha-receptor agonists (e. g. norepinephrine) may have important inotropic activity in congestive cardiac failure where there has been down-regulation of the β-receptors.
KeywordsAdenosine Catecholamine Cardiol Fentanyl Triphosphate
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