Changes in plasma insulin in response to a physiological or pathophysiological elevation in circulating atrial natriuretic factor (ANF) have been investigated. Plasma insulin, glucose, immunoreactive (ir) ANF, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), absolute and fractional excretion of sodium (FENa), have been measured in 14 volunteers before and during infusion of low doses of ANF or vehicle (V). Each subject received single-blind in a randomized sequence at 2 week-intervals: V alone, or ANF 4, 8 and 16 ng.kg-1.min-1, induced over 90 min. Plasma irANF was increased 2.5- to 11-fold during the ANF infusion as compared to the test with the vehicle. Plasma insulin did not change during V administration (baseline vs V: 22 vs 21 microU.ml-1) and was unchanged during ANF at 4, 8 and 16 ng.kg-1.min-1 (19, 19, 21 microU.ml-1, respectively). Blood pressure, ERPF and GFR were not affected, and diuresis, FENa and urinary Na excretion were increased significantly and dose-dependently during ANF, but not V infusion. Compared to baseline, ANF 4, 8 and 16 ng.kg-1.min-1 increased urinary Na excretion by 147,241 and 446 mumol.min-1, respectively. The findings indicate that, in normal humans, an acute increase in irANF within or slightly above the physiological range, which modified natriuresis and diuresis, did not alter circulating plasma insulin.