Natriuretic peptides in water-deprived and in salt-loaded rats

To elucidate the differences of physiological function of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), we measured tissue concentration and mRNA level in cardiac atrium, ventricle, and brain as well as plasma concentration of these three peptides in water-deprived (WD) and in salt-loaded (SI.) rats. WD rats were given no water for 5 days, whereas SL rats had free access to 2% saline for 14 days. Plasma ANP and BNP concentration of the WD group decreased to 21% and < 10%, and the concentration of the SL group to 36% and 47% of the control (CON) group. Atrial and ventricular BNP concentration of the WD group decreased to 36% and 23% of the CON group, and atrial BNP concentration of the SL group decreased to a lesser extent. BNP mRNA level in atrium and ventricle decreased in both the WD and SL groups, with the WD group showing larger decreases to 11% and 20% of the CON group. ANP mRNA level in atrium and ventricle of the WD group decreased to 40% and 61% of the CON group, but increased to 147% in ventricle of the SL group. In the brain, no significant change was observed in ANP and CNP concentration in both the WD and SL group. Under these conditions. BNP generally showed larger changes than ANP in both peptide concentration and mRNA level. Gene transcription and peptide production of ANP and BNP in atrium and in ventricle were not always found to be in concert, especially in the case of salt loading. Taken as a whole, our results demonstrate differences among the systems regulating biosynthesis and secretion of ANP and BNP in atrium and ventricle.