It is a 28 amino acid peptide. Secretion by myoendocrine cells in the atrial muscle as a 151 amino acid pre-pro-ANP precursor leads to processing to a 126 amino acid pro-ANP, which is stored in secretory granules. It is primarily released from atria in response to volume expansion, which is sensed as an increase in atrial stretch. The right atrium maybe quantitatively more important. Other causes for the stimulation of secretion include angiotensin II, endothelin and beta-adrenergic stimulation.
The end-organ vasoactive, natriuretic and diuretic effects are mediated through binding with guanyl cyclase receptors. Atrial natriuretic peptide promotes natriuresis by causing increased glomerular filtration rate, with simultaneous fall in arterial blood pressure. This is achieved by dilatation of the afferent arteriole and constriction of the efferent arteriole of the glomerulus. Thereby the filtered sodium load is increased. Other actions include: Inhibition of renin secretion, aldosterone production and vasopressin secretion; Inhibition of vasopressin-induced water reabsorption in the collecting ducts;
» Inhibition of angiotensin-II and aldosterone-induced sodium reabsorption in l the distal tubule;
Promotion of arterial vasodilatation;
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