Atrial natriuretic peptide (ANP) is a polypeptide secreted by atrial cardiomyocytes in response to increased intravascular pressure (determined by atrial volumetric stretch). ANP secretion leads to peripheral vasodilation, natriuresis and diuresis, ultimately lowering blood pressure and increasing glomerular filtration rate (GFR)).
ANP binds to the natriuretic peptide receptor A (NPR-A) on cell membranes, activating guanylate cyclase and forming cyclic GMP. The NPR-A receptor is present in the following tissues:
1. Kidney: ANP dilates afferent atrioles preferentially, leading to an increase of GFR. ANP also binds along the nephron, limiting the reabsorption of sodium and restricting renin secretion.
2. Vasculature: ANP relaxes smooth muscle in arterioles and venules
3. Adrenal: Restricts the release of aldosterone
Doust et al. review the use of BNP testing clinically in patients with suspected heart failure. Brain natriuretic peptide (BNP) levels are simple and objective measures of cardiac function. Elevated BNP measurements can be used to diagnose heart failure. The high negative predictive value of BNP tests is particularly helpful for ruling out heart failure.
Daniels et al. provide a review of the function of natriuretic peptides. Natriuretic peptides (NPs) are released from the heart in response to pressure and volume overload. The NP level reflects a compilation of systolic and diastolic function, as well as right ventricular and valvular function. NP levels have important prognostic value in multiple clinical settings, including in patients with stable coronary artery disease and with acute coronary syndrome. Troughton et al report that NP-guided heart failure (HF) therapy has recently been given a recommendation in US HF guidelines to achieve guideline-directed medical therapy and possibly improve outcomes.
Illustration A depicts a flowchart of the end-organ effects of atrial natriuretic peptide.
Answer 1: Increased water reabsorption by the renal collecting ducts results from the effects of antidiuretic hormone (vasopressin).
Answer 2: Vasoconstriction, increased blood pressure, and aldosterone release result from action of angiotensin II.
Answer 4: Increased renal absorption of sodium and water results from the effects of aldosterone.
Answer 5: Increased plasma calcium and decreased renal reabsorption of phosphate result from the effects parathyroid hormone (PTH).
Doust J, Lehman R, Glasziou P. The role of BNP testing in heart failure. Am Fam Physician. 2006 Dec 1;74(11):1893-8. Review
PMID:17168346 (Link to Abstract)
Daniels LB, Maisel AS. Natriuretic peptides. J Am Coll Cardiol. 2007 Dec 18;50(25):2357-68. Review.
PMID:18154959 (Link to Abstract)
Troughton R, Michael Felker G, Januzzi JL Jr. Natriuretic peptide-guided heart failure management. Eur Heart J. 2014 Jan;35(1):16-24. doi: 10.1093/eurheartj/eht463. Epub 2013 Nov 11
PMID:24216390 (Link to Abstract)
USMLE World Step 1 QBank Question #1978. Copyright © USMLEWorld, LLC 2012