Abnormal circulating protein concentration Decreased circulating NT-proANP concentration 2024-04-03T07:43:55Z The concentration of NT-proANP (= N-terminal proatrial natriuretic peptide) in the blood circulation is below the lower limit of normal. The 126-amino acid peptide atrial natriuretic peptide pro-hormone (proANP1-126) is synthesized and stored in atrial myocytes. Upon distension of the cardiac atria, proANP(residues 1-126) is cleaved and equimolar amounts of the C-terminal fragment proANP(99-126) (ANP) and an N-terminal fragment (proANP(1-98) are secreted from the atria. The N-terminal fragment is subsequently cleaved into smaller peptide fragments, which have natriuretic, diuretic, blood pressure-lowering and kaliuretic properties. ANP is a potent mediator of natriuresis and vasodilatation. Whereas ANP is rapidly removed from the circulation [10], the N-terminal fragments, such as the proANP(1-30) fragment (Nt-proANP), which is also termed long-acting natriuretic peptide and has strong salt-excreting properties itself, are stable and remain in the circulation at manifold higher concentrations than ANP. Nt-proANP measured in peripheral plasma is therefore less prone to fluctuation and may thus be a more reliable measure of atrial ANP secretion than peripheral plasma concentration of ANP itself. Reduced long-acting natriuretic peptide concentration