MODULATION BY LOCALLY PRODUCED LUMINAL ANGIOTENSIN-II OF PROXIMAL TUBULAR SODIUM-REABSORPTION VIA AN AT(1) RECEPTOR

The concentration of angiotensin II reported in proximal tubular fluid in anaesthetized rats is considerably higher than in plasma, indicati ng secretion of this peptide into the tubular lumen. Shrinking split-d rop micropuncture was used to examine the effect of endogenous angiote nsin on sodium and water absorption in the proximal convoluted tubule. Addition of losartan, a nonpeptide ATI receptor blocker, to intratubu lar fluid increased fluid uptake by 15.7+/-3.9% (10(-5) M) and 24.7+/- 9.4% (10(-4) M) whereas the AT(2) inhibitor, PD123319 had no effect. W e conclude that angiotensin II is secreted into proximal tubular fluid and, in the anaesthetized rat, is maintained at a concentration that inhibits sodium and water transport via AT(1) receptors.