Changes in plasma atrial natriuretic polypeptide concentration during head-out water immersion and saline infusion in normal men.

The physiological mechanism regulating secretion of human atrial natriuretic polypeptide (hANP) was examined by measuring plasma hANP by a specific radioimmunoassay during head-out total body water immersion (WI) and saline infusion in normal men. Seven healthy men were immersed in water for 1 hour, 6 normal men and women were given an infusion of 1 liter of normal saline over 1 hour and 8 normal men were given a similar infusion over 2 hours. During WI, the urinary volume (UV) and urinary Na excretion (UNaV) increased significantly, and the plasma hANP level increased significantly from 246 +/- 12 (mean +/- SE) pg/ml to 392 +/- 32 pg/ml after 35 +/- 5 min, but returned to the basal level after 90 min. The increase in hANP level was correlated with an increased UNaV between 30 to 60 min during WI. The plasma norepinephrine, renin activity, aldosterone and cortisol levels also decreased during WI. Saline infusion caused variable increases in the hANP level: the mean peak values of hANP and times of the peaks from the start of saline infusion were respectively 305 +/- 30 pg/ml after 30 +/- 3 min of infusion at a rate of 1L/1 hr and 285 +/- 25 pg/ml after 69 +/- 15 min of infusion at a rate of 1L/2 hrs. The time of the peak of plasma hANP during infusion at 1L/2 hrs was significantly longer than the peaks for WI or an infusion of saline at 1L/1 hr. Moreover, the peak hANP level was significantly smaller during either condition of saline infusion than during water immersion. These results indicate that i) acute central hypervolemia caused by WI increases hANP secretion, and this increase may participate in natriuresis during WI, and ii) saline infusion causes an increase in plasma hANP of variable magnitude, the increase being more rapid for a more rapid infusion of saline. This suggests that hANP is released into the circulation by acute volume expansion and plays a physiologically important role in maintaining blood volume homeostasis in man.