Preferential increase in the free form of atrial natriuretic peptide in adriamycin-induced nephrotic rats.

In order to evaluate the pathophysiologic role of a free form of atrial natriuretic peptide (ANP) in the nephrotic syndrome, the plasma concentration of immunoreactive ANP was measured by radioimmunoassay using direct (unextracted) and extraction methods in adriamycin-induced nephrotic and normal control rats. The ir-ANP levels measured using unextracted or extracted plasma were representative of total and the free form of ANP, respectively. The plasma levels of total and the free form of ANP were significantly higher in nephrotic rats than in controls (p less than 0.01, p less than 0.001). However, plasma levels of the bound form of ANP, calculated by subtracting the free form of ANP from total ANP, were comparable between the two groups. The free form of ANP was inversely correlated with the daily urinary sodium excretion (r = -0.71, p less than 0.001) and plasma albumin (r = -0.83, p less than 0.001), and positively correlated with the daily urinary protein excretion (r = -0.85, p less than 0.001) in both control and nephrotic groups. Based on these results, the preferential increase in the free form of ANP in nephrotic rats is considered to be a compensatory phenomenon induced by the decreased renal ability to eliminate sodium and water. An increase in the free form of ANP may have some role in urinary protein excretion in the nephrotic syndrome.