Atrial natriuretic factor plays a significant role in body fluid homeostasis

Atrial natriuretic factor (ANF) is a hormone with the physiological characteristics of a regulator of body fluid volume. It is potent, has a short duration of action, and responds to a physiologically relevant stimulus in a negative feedback-controlled system. It can act directly or indirectly (via inhibition of aldosterone biosynthesis) on the kidney to alter sodium transport and may regulate fluid distribution within the extracellular space. The peptide circulates at low (nanomolar) levels, and recent studies with renal inner medullary cells document relevant receptor binding and second messenger activation in this concentration range. In vivo data support a direct action on the kidney to enhance natriuresis, and blockade of a primary catabolic pathway for ANF within the kidney results in augmented natriuresis at concurrent endogenous peptide concentrations. Long-term, low dose infusion directly into the renal artery of conscious dogs supports a physiological action of ANF to promote urinary sodium excretion. Nevertheless, under certain circumstances, natriuresis does not occur even at high circulating levels of ANF. Apparently other factors such as renal perfusion pressure, volume status, and renal nerve activity are important in determining the natriuretic response to a given level of peptide. We hypothesize that the role played by ANF in volume regulation is highly complex, and the kidney responds with increased sodium excretion only when a constellation of variables is appropriately arrayed. That is, ANF is a necessary, but not sufficient, condition to induce natriuresis.