Natriuretic Peptides and Cardiac Endocrine Function

The heart is not only a pump but also an endocrine organ: when its chambers are stretched by increased blood volume or pressure, cardiac muscle cells release natriuretic peptides. Atrial natriuretic peptide and B-type (brain) natriuretic peptide act on the kidney and blood vessels to promote sodium and water excretion and to lower blood pressure, opposing volume overload. This topic covers the cardiac endocrine system and its role in fluid and blood-pressure balance.

Definition

Natriuretic peptides are hormones released by cardiac muscle cells in response to wall stretch; the principal forms, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), promote sodium and water excretion and vasodilation, counteracting increases in blood volume and pressure.

Scope

The entry covers the major natriuretic peptides (ANP and BNP), the stimulus of myocardial stretch that triggers their release, and their actions on the kidney and vasculature to regulate volume and pressure. It treats cardiac endocrine function as a reference physiology topic and does not provide diagnostic thresholds or treatment guidance.

Core questions

• What stimulus causes the heart to release natriuretic peptides?
• How do ANP and BNP act on the kidney and blood vessels?
• How does the cardiac endocrine system counterbalance volume and pressure overload?

Key concepts

• Atrial natriuretic peptide (ANP)
• B-type natriuretic peptide (BNP)
• Myocardial wall stretch as stimulus
• Natriuresis and diuresis
• Vasodilation and blood-pressure regulation
• The heart as an endocrine organ

Mechanisms

Increased intravascular volume or pressure stretches the walls of the cardiac chambers, stimulating cardiomyocytes to release natriuretic peptides; ANP is stored mainly in atrial granules, while BNP is produced largely by the ventricles. These peptides bind natriuretic-peptide receptors that raise intracellular cyclic GMP, promoting sodium and water excretion by the kidney, relaxing vascular smooth muscle, and opposing the renin-angiotensin-aldosterone system. The net effect is to reduce blood volume and pressure, forming a hormonal counter-regulatory limb to volume overload.

Clinical relevance

Because their release reflects cardiac wall stress, natriuretic peptides are widely studied in the context of heart failure and fluid balance, where circulating BNP is used as a marker of cardiac strain. This entry describes the underlying physiology for educational orientation and does not provide diagnostic cut-offs or treatment recommendations.

Evidence & guidelines

The cardiac endocrine concept began with de Bold and colleagues' 1981 demonstration that atrial extract produces a rapid natriuretic response, identifying ANP. Sudoh and colleagues then described a second peptide, BNP, in 1988. Reviews have synthesised the physiology and signalling of the natriuretic-peptide family. The topic rests on this primary and review literature.

History

In 1981 Adolfo de Bold and colleagues showed that injecting atrial muscle extract caused a rapid and potent natriuresis, providing the first clear evidence that the heart secretes a hormone and leading to the identification of atrial natriuretic peptide. In 1988 Sudoh, Matsuo, and colleagues isolated a related peptide from brain that proved to be of mainly cardiac (ventricular) origin, named B-type natriuretic peptide, establishing the natriuretic-peptide family.

Key figures

• Adolfo J. de Bold
• Hisayuki Matsuo
• Kenji Kangawa

Seminal works

• debold-1981
• sudoh-1988

Frequently asked questions

Why is the heart considered an endocrine organ?

Cardiac muscle cells secrete natriuretic peptides into the bloodstream in response to wall stretch, and these hormones act on distant organs such as the kidney, which is the defining feature of endocrine signalling.

What do natriuretic peptides do?

They promote excretion of sodium and water by the kidney and relax blood vessels, lowering blood volume and pressure and counteracting volume overload.