The renal response to acute hypervolemia is caused by atrial natriuretic peptides.

In anesthetized rats, synthetic rat atriopeptin II produced an increase in urinary volume and sodium excretion as well as a decrease in arterial blood pressure. Both the natriuretic and hypotensive effects were blocked by monoclonal antibodies directed against atriopeptin II. The diuresis and natriuresis caused by furosemide was not inhibited by these antibodies. Thus, the monoclonal antibodies provide a specific inhibitor for atriopeptin-mediated responses in vivo and can be used to investigate the role of atriopeptin in volume regulation. Volume expansion with 20 ml/kg i.v. homologous blood induced strong diuresis and natriuresis in the anaesthetized rat. This response was also blocked by the described monoclonal antibodies. A radioimmunoassay for the determination of atriopeptin-like immunoreactivity (ANP-IR) is described. The plasma levels of ANP-IR 8 min after blood injection were 3-4 times higher than in control rats. Thus, the strong diuresis observed after volume expansion is due to an increase in circulating atrial natriuretic peptides that obviously exert a regulative function in fluid volume control.