MECHANISMS UNDERLYING THE DECREASE IN CIRCULATING ANGIOTENSIN-II CONCENTRATION AFTER SODIUM LOADING

1, Acute sodium loading causes a rapid decrease in the circulating con centration of angiotensin II (AngII), which is apparent from 5 min aft er sodium administration. This could result from an increase in AngII catabolism and/or a decrease in AngII synthesis/secretion, However, th e major determinant of AngII synthesis is thought to be a change in pl asma renin activity, which occurs over a longer time frame (15 min). 2 , To investigate the mechanisms underlying the rapid decrease in plasm a AngII engendered by sodium administration, we performed metabolic cl earance studies in male New Zealand white rabbits before and after a h ypertonic sodium load of 1.5 mmol/kg as 0.513 mol/L saline i,v, bolus, 3, The metabolic clearance rate of AngII increased significantly from 42.2 +/- 9.0 mL/min per kg before sodium to 110.8 +/- 33.7 mL/min per kg after sodium administration (P < 0.05), The calculated or theoreti cal secretion rate decreased from 1470.7 +/- 404.2 to 573.5 +/- 139.5 fmol/min per kg (P < 0.025) in response to sodium, 4, We conclude that an increase in AngII metabolism and a decrease in synthesis/secretion contribute to the reduction in circulating AngII, which occurs in the first 60-90 min after sodium loading.