Although the heart had long been considered merely a muscular pump that performed the physical labor of the circulation, it has been recognized for over five decades that in addition to the contractile ultrastructure, a secretory function was evidenced by the presence of dense-core granules in the myocytes. In the past decade, the endocrine nature of the heart has been established, and the physiology and pathophysiology of the cardiac hormones have been extensively characterized. The myocyte produces both constitutively and in a regulated fashion two members of a class of hormones designated natriuretic peptides on the basis of their abilities to stimulate salt and water excretion by direct renal actions and indirect effects on other tissues, including endocrine organs, responsible for the control of fluid and electrolyte homeostasis. Two members of the natriuretic peptide family, atrial natriuretic peptide (A-type natriuretic peptide, ANP) and brain natriuretic peptide (BNP, actually a misnomer, since although cloned from a brain library, little of this isoform is present in brain) are produced in the heart and released in response to a variety of cues, all typical of plasma volume overload or hyperosmolality. Although numerous biological actions have been characterized, their hallmark effects are to unload the vascular tree via a combination of central nervous system, pituitary, adrenal, vascular, and renal actions (Fig. 1). This results in decreased venous return to the pump as a consequence of increased renal excretion of water and solute, vasorelaxation in certain vascular beds, increased capillary permeability, and decreased cardiac output. The third member of this family of hormones, although exerting many of the same actions as ANP and BNP, is unique in that it is predominantly produced in the vascular endothelium, not the heart, and is thought to act more in a paracrine fashion, regulating primarily vascular tone and growth. Additionally, this hormone, designated C-type natriuretic peptide (CNP), exerts several central nervous system actions that oppose those of ANP and BNP.
KeywordsNitric Oxide Natriuretic Peptide Brain Natriuretic Peptide Atrial Natriuretic Peptide Guanylyl Cyclase
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