Observations on the natriuretic response to intravenous infusions of atrial natriuretic factor in water-loaded anaesthetized rats.

Natriuresis induced by infusions of atrial natriuretic factor (ANF) in water-loaded rats typically occurred in time sequences ('peak-and-shoulder' patterns) with an overlap of two different natriuretic responses. The first response was abrupt, short-lived and potentiated by angiotensin converting enzyme (ACE) inhibition. The second response was a gradual onset of natriuresis which lasted only as long as the ANF infusion and was directly correlated to the level of arterial blood pressure. This phenomenon explains the apparent loss of responsiveness to ANF bolus injections during a late phase. Atrial natriuretic factor facilitated excretion of intravenous salt loads, and the effect was also observed with low salt doses (1 microgram/h) which were below threshold for natriuresis when given alone. The data available so far suggest that ANF, apart from its effect on collecting-duct permeability, interferes with several control and feedback systems involved in sodium input into the collecting-duct system.