Atrial Natriuretic Factor: History, Structure, Production and Effects
Atrial Natriuretic Factor (ANF), also called Atrial Natriuretic Peptide (ANP), is a cardiac hormone secreted by atrial muscles in response to increased blood volume. It promotes sodium and water excretion, reduces blood pressure, and prevents cardiac hypertrophy. ANF also serves as a sensitive biomarker in heart failure.
This Story also Contains
- What is Atrial Natriuretic Factor?
- ANF Hormone
- History of Atrial Natriuretic Factor
- Structure and Production of ANP
- Actions Of ANF
- ANF As Biomarker
- Atrial Natriuretic Factor NEET MCQs
- FAQs on Atrial Natriuretic Factor
Atrial Natriuretic Factor, abbreviated as ANF, is a peptide hormone secreted by the cardiac atria in humans. It is also named the Atrial Natriuretic Peptide (ANP). ANF helps to maintain the chemical coordination and integration of the body. It is secreted by the cardiac muscles in the atrial walls of the heart. The hormone works on reducing blood volume in response to the stretching of the atrial wall corresponding to an increase in the blood volume in the atria. It has associated effects following this volume reduction. These secondary effects include reduced extracellular fluid (ECF), a decrease in blood pressure, and increased potassium content. There are specific regulatory mechanisms to counter these changes in the body.
What is Atrial Natriuretic Factor?
The ANF (ANP) is released by cells in the atria of the heart, lowers blood pressure by causing vasodilation and by promoting the loss of salt and water in the urine, which reduces blood volume. ANP is a cardiac signaling molecule acting as a diuretic that inhibits the reabsorption of sodium by the kidneys. The stretching of the atria of the heart stimulates secretion of ANP. After releasing, it relaxes mesangial cells in glomerulus and increases capillary surface area available for filtration.
ANF Hormone
ANF hormone gets secreted by the action of the NPPA gene in humans. It increases sodium excretion from the body through the renal fluid (urine), causing reduced extracellular fluid volume and associated secondary effects. The importance of this hormone lies in the fact that it is vital in cardiac development. The malfunctioning of this gene can lead to cardiac problems due to changes in ANP levels. ANP is found in amphibians, mammals, and bony fishes. It is absent in cartilaginous fishes, reptiles, and birds.
History of Atrial Natriuretic Factor
A cardiovascular researcher, Adolfo José be Bold, first identified the natriuretic factor in rats in 1981. The atrial extracts of rats show a factor that increased the water and salt excretion. This factor was successfully separated and purified from the heart tissue and was named the Atrial Natriuretic Factor (ANF).
Structure and Production of ANP
ANP is a peptide hormone with 28 amino acid peptides and a 17 amino acid ring in the middle. It is one of the nine in the family of structurally similar hormones of natriuretic nature, and seven are of atrial origin.
ANP is initially synthesized as an inactive hormone (preprohormone - a precursor to peptide hormone). The coding of the hormone is by the NPPA gene on chromosome 1. The cleavage of the signal peptide, a sequence of 25 amino acids, forms proANP (126 amino acid peptide) and is stored in the atrial granules.
On the stimulation of the atrial walls, proANP gets converted to a 28 amino acid mature ANP. It can happen due to several reasons.
An increased sodium concentration is known as hypernatremia.
The stretching of atrial walls.
Increase in Endothelin, a vasoconstrictor.
Actions Of ANF
Kidney - It increases the excretion of water and sodium by increasing the glomerular filtration rate. The increased blood flow through the vasa recta removes the sodium solutes. The reduced sodium reabsorption by the ascending limb of nephrons and deactivation of the renal SNS (Sympathetic Nervous System) also adds to the effect. The hormones like aldosterone (which promotes sodium conservation) and angiotensin (which increases blood pressure by blood vessel constriction) are inhibited as ANPs inhibit renin secretion. All of these result in decreased sodium reabsorption.
Cardiac effect - ANP helps to inhibit cardiac hypertrophy (thickening of heart muscles, which makes it harder for the heart to pump blood) by inhibiting calcium influx. Fibrosis is also prevented by decreasing inflammation and preventing fibroblasts from entering and replicating in the heart tissues.
Adipose tissue - It releases the fatty acids stored in adipose tissues. The infusion of ANP can increase glycerol plasma concentrations in humans.
Immune system - ANP produced by the immune cells helps to raise the defence. It acts against the extracellular microbes and gives cytoprotective effects (protection against harmful agents).
Commonly Asked Questions
Atrial Natriuretic Factor (ANF), also known as Atrial Natriuretic Peptide (ANP), is a hormone produced by heart muscle cells in the atria. It's important because it plays a crucial role in regulating blood pressure, blood volume, and sodium balance in the body. ANF acts as a natural diuretic and vasodilator, helping to lower blood pressure and reduce fluid retention.
ANF primarily binds to natriuretic peptide receptor-A (NPR-A), a guanylyl cyclase-linked receptor. When ANF binds to NPR-A, it activates the receptor's guanylyl cyclase domain, leading to increased production of cyclic guanosine monophosphate (cGMP). This second messenger then triggers various cellular responses that mediate the physiological effects of ANF.
ANF As Biomarker
ANP can be used as a biomarker in various cardiovascular disorders, including stroke, heart failure, and myocardial infarction.
MRproANP (Mid-Regional Pro-Atrial Natriuretic Peptide) is a precursor of ANP that is an extremely sensitive biomarker in heart failure. Its levels above 120 pmol/L indicate possible heart failure.
Atrial Natriuretic Factor NEET MCQs
Q1. Which one of the following hormones that control blood pressure is secreted by the human heart?
Erythropoietin
Atrial natriuretic factor
ACTH
Glucocorticoid
Correct answer: 2) Atrial natriuretic factor
Explanation:
When the blood volume or blood pressure increases it applies a force on the wall of the atria and causes it to stretch. In response to increased pressure or volume and thereafter atrial wall stretch, a peptide hormone is produced in the heart called Atrial natriuretic peptide (ANP) or Atrial natriuretic factor (ANF) and it is released into the circulation.
ANF is responsible for blood pressure control and body fluid homeostasis. It is produced by myocytes in the atria and is released in response to the stress of the local wall. When it is released into the circulation it causes increases in glomerular filtration rate (GFR), inhibition of sodium ion transport, and suppression of the renin release. ANP induces Natriuresis and diuresis by shutting down the system of renin-angiotensin-aldosterone that causes vasodilation and the reduction of blood pressure. When the blood vessel expands, the excretion of water and sodium increases and stabilizes the blood pressure and blood volume. The reduced blood pressure is the consequence of diminished cardiac output, decreased intravascular volume and peripheral vascular resistance.
Hence, the correct answer is option (2) Atrial natriuretic factor.
Q2. Statement 1- Anti natriuretic factor is released to decrease blood pressure by inhibiting the release of renin from the juxtaglomerular cells of the kidney.
Statement 2 - Antidiuretic hormone(ADH), anti-natriuretic factor (ANF) and renin-angiotensin-aldosterone system(RAAS) regulate kidney functioning to maintain osmolarity, salt concentration and blood pressure.
Statement 1 and statement 2 both are right.
Statement 1 is wrong, Statement 2 is right.
Statement 2 is wrong, Statement 1 is right.
Both statements are wrong.
Correct Answer: 1) Statement 1 and statement 2 both are right.
Explanation:
A peptide hormone that is secreted by cardiocytes is Atrial natriuretic factor (ANF). The anti-natriuretic factor is released to decrease blood pressure by inhibiting the release of renin from the juxtaglomerular cells of the kidney. Hormone(ADH), anti-natriuretic factor (ANF) and renin-angiotensin-aldosterone system(RAAS) regulate kidney functioning to maintain osmolarity, salt concentration and blood pressure.
Hence, the correct answer is option 1. Statement 1 and statement 2 both are right.
Q3. Statement 1- A peptide hormone that is secreted by cardiocytes is the Atrial natriuretic factor (ANF) which inhibits the release of renin from the juxtaglomerular cells of the kidney.
Statement 2 - ANF is a hormone that drops blood pressure by relaxing arteriole and venules and by increasing capillary permeability.
Statement 1 and statement 2 both are right.
Statement 1 is wrong, Statement 2 is right.
Statement 2 is wrong, Statement 1 is right.
Both statements are wrong.
Correct answer: 1) Statement 1 and statement 2 both are right.
Explanation:
A peptide hormone that is secreted by cardiocytes is Atrial natriuretic factor (ANF). Which inhibits the release of renin from juxtaglomerular cells of the kidney. ANF is a hormone that drops blood pressure by relaxing arteriole and venules and by increasing capillary permeability.
Hence, the correct answer is option 1. Statement 1 and statement 2 both are right.
Also Read:
FAQs on Atrial Natriuretic Factor
What is atrial natriuretic factor?
Atrial Natriuretic Factor (ANF), also called Atrial Natriuretic Peptide (ANP), is a hormone secreted by the atrial walls of the heart in response to increased blood volume and pressure. It helps regulate fluid balance, blood pressure, and sodium levels in the body. ANP acts mainly on the kidneys, blood vessels, and adrenal glands.
What is the role of ANP in the kidney?
In the kidneys, ANP promotes natriuresis (excretion of sodium in urine) and increases water loss. It dilates the afferent arterioles, increasing glomerular filtration rate (GFR), and inhibits sodium reabsorption in the collecting ducts. This leads to reduction in blood volume and blood pressure. ANP also suppresses renin and aldosterone secretion, further helping in fluid regulation.
Who discovered atrial natriuretic peptide?
ANP was first discovered in 1981 by Adolfo J. de Bold, a Canadian cardiovascular scientist. He observed that extracts from atrial tissue could cause rapid sodium excretion in rats, leading to the identification of ANP as a heart-derived hormone. His discovery revealed the endocrine function of the heart.
How is ANP used as a biomarker?
ANP and related peptides (like BNP – Brain Natriuretic Peptide) are used as biomarkers for heart failure and cardiovascular diseases. Elevated ANP levels in blood indicate increased atrial stretch and pressure, commonly seen in conditions like congestive heart failure, hypertension, and atrial fibrillation. Measuring ANP helps in diagnosis, prognosis, and monitoring of heart-related disorders.
Frequently Asked Questions (FAQs)
ANP (ANF) has several effects on the body.
ANP increases the glomerular filtration rate in the kidney.
ANP inhibits the reabsorption of sodium and water in the nephrons. It results in reduced secretion of renin and subsequent inhibition of aldosterone and angiotensin (renin-angiotensin-aldosterone system or RAAS).
Natriuretic peptides have a role in fat oxidation in the skeletal muscles.
It increases blood pressure levels.
Aldosterone and ANP are related, wherein lower ANP levels can lead to hypertension.
ANP plays a role in lipid movement inside the adipose tissue.
ANP can be predictive of diabetes and could be used in treating obesity if its lifetime could be increased.
The Bowman's capsule is a cup-like sac at the beginning of a nephron. It encloses a glomerulus which is a mass of blood capillaries. The volume of fluid (filtrate) passing from the glomerulus to the Bowman's capsule in a unit of time (after filtration) is called the glomerular filtration rate.
The B-type (Brain) Natriuretic Peptide (BNP) and C-type Natriuretic Peptide (CNP) are similar in structure to ANP. However, ANP and BNP are produced in the heart cells, while CNP is related to the central nervous system.
ANF has several names, including ANF (Atrial Natriuretic Factor), Atriopeptin, Atrial Natriuretic Hormone, Cardiodilantin, and Cardionatrine.
Diuretics are the common name for medications administered to decrease the excess water content in the body by promoting diuresis (urine production). It also helps in the subsequent lowering of blood pressure. The ANF hormone is a diuretic hormone.
ANP stands for Atrial Natriuretic Peptide and ANF stands for Atrial Natriuretic Factor. Both are the names of the peptide hormone secreted by the atrial muscles.
