" Atrial natriuretic peptide (ANP) is the main natriuretic hormone; it is a 28-amino-acid polypeptide that is released from myocardial cells in the atria and in some cases the ventricles. ANP stimulates natriuretic peptide receptors (NPR) in the glomeruli and inner medullary collecting ducts.
This peptide functions as a direct vasodilator and also increases urinary sodium and water excretion. The latter effect is mediated by various renal and extra renal changes. The natriuretic action is primarily caused by inhibition of sodium reabsorption in the medullary collecting tubule. There still is controversy about the same effect on the proximal tubule, but in case of high ANP levels glomerular filtration rate is increased, which also leads to natriuresis.
But there are other pathways through which ANP exercises its natriuretic and diuretic effects, such as through the effect on the renin-angiotensin-aldosterone system. In the proximal tubule, ANP inhibits the angiotensin-mediated sodium and fluid reabsorption. Besides that, ANP antagonizes the actions of aldosterone and of ADH.
Brain natriuretic peptide: Brain natriuretic peptide (BNP) is homologous to ANP and is present in both the brain and the heart. Circulating concentration of BNP is less than 20% of that of ANP, but in congestive heart failure patients it can easily exceed these rates. The physiologic role of BNP remains to be determined, but it definitely plays a role in volume status. In ten male volunteers volume loading with an infusion of 15 ml/kg of 0.9% NaCl led to a short-lasting increase of plasma NT-pro-ANP (prohormone of ANP) and a delayed increase in plasma NT-pro-BNP, together with a parallel increase in urine flow, renal excretion of sodium and NT-pro-BNP. The increased urinary NT-pro-BNP excretion during volume loading suggests a possible role of BNP in sodium homeostasis in men. In a study on 74 male subjects aged 50 or older a correlation between increased NT-pro-BNP and leg edema has been found. Furthermore, BNP is used for volume estimation in dialysis patients, since BNP level variations correlate positively with volume status alterations in this specific patient group.
(An-Sofie Goessaert, Johan Vande Walle, Ayush Kapila and Karel Everaert- Hormones and Nocturia: Guidelines for Medical Treatment?)
Last date updated on June, 2014