Where is it produced and which system does it belong to?
Atrial natriuretic peptide belongs to hormones synthesized outside classical endocrine glands. The heart exhibits hormonal activity within the system of extraglandular hormone production.
- Right atrium: cardiomyocytes of this region secrete atrial natriuretic peptide (ANP, A-type natriuretic peptide).
- Cardiac ventricles: produce other natriuretic hormones; B-type natriuretic peptide (BNP) is secreted by the cardiac ventricles in response to overstretching caused by an excessive increase in circulating blood volume.
Hormonal activity is also exhibited by other organs: kidneys (renin secretion by the juxtaglomerular apparatus and erythropoietin by interstitial cells), gastrointestinal tract (APUD system cells secreting polypeptide hormones), central nervous system (neuroendocrine peptides, e.g., endorphins), and thymus. Prostaglandins, thromboxane, and prostacyclin are also classified as hormone-like substances.
Mechanism of action at the cellular level
- Receptor type: natriuretic peptides—atrial (ANP, A-type natriuretic peptide) and brain (BNP, B-type natriuretic peptide)—are ligands for guanylyl cyclase-coupled receptors. This is the smallest family of transmembrane receptors.
- Intracellular cascade: ligand binding stimulates the intrinsic guanylyl cyclase activity of the receptor.
- Second messenger: guanosine triphosphate (GTP) is converted into cyclic guanosine monophosphate (cGMP).
Physiological example: B-type natriuretic peptide is secreted by the cardiac ventricles in response to overstretching caused by an excessive increase in circulating blood volume. Via increased cGMP, it dilates blood vessels and enhances sodium and water excretion.
Pathophysiology and clinical significance
In nephrotic syndrome, atrial natriuretic peptide is considered a potent regulator of water-sodium metabolism.
The paradox of edema development in the absence of hypovolemia is explained by the kidneys losing their sensitivity to ANP: its activity on renal tissue is reduced.
Systemic homeostasis disorders include:
- development of hypo-oncotic edema with sodium and water retention;
- hormonal imbalance: secondary hyperaldosteronism, increased plasma renin and catecholamine activity;
- metabolic shifts: hyperlipidemia, trace element loss, hypercoagulation.
Do not confuse: other meanings of the abbreviation ANP
In the provided materials, the abbreviation "ANP" is also used to refer to progressive supranuclear palsy and polyneuropathy: for example, diabetic polyneuropathy or nervous system damage associated with psychoactive substance use.
Class and exam questions
Which family do natriuretic peptide receptors belong to?
They belong to guanylyl cyclase-coupled transmembrane receptors. This is the smallest family of transmembrane receptors.
How do natriuretic peptides act at the intracellular level?
Ligand binding stimulates the intrinsic guanylyl cyclase activity of the receptor. As a result, GTP is converted into cGMP.
Why doesn't ANP prevent edema in nephrotic syndrome?
In nephrotic syndrome, the kidneys lose sensitivity to ANP: its activity on renal tissue is reduced. Consequently, hypo-oncotic edema develops with sodium and water retention.
What other natriuretic peptides are produced in the heart?
The cardiac ventricles produce other natriuretic hormones. B-type natriuretic peptide (BNP) is secreted by the cardiac ventricles in response to overstretching caused by an excessive increase in circulating blood volume.
What else to study on this topic
- Diffuse endocrine system (extraglandular hormone production)
- Guanylyl cyclase-coupled receptors
- Pathogenesis of nephrotic syndrome
- Brain natriuretic peptide (BNP)
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