INTERACTION OF ATRIAL-NATRIURETIC-FACTOR AND ANGIOTENSIN-II IN PROXIMAL HCO3-REABSORPTION

Bicarbonate reabsorption was evaluated by the acidification kinetics technique in middle proximal tubule in Munich-Wistar rats. Atrial natriuretic factor (ANF) and angiotensin II (ANG II) were infused into the jugular vein (ANF, 0.5-mu-g.min-1.kg-1 after a prime of 10-mu-g/kg; ANG II, 20 ng.min-1.kg-1) or added to luminal or peritubular perfusion fluid (10(-6) M ANF; 10(-12) M ANG II). In the presence of ANF, in each condition, no significant differences in net HCO3- reabsorption or in acidification half time were observed compared with the control group. In the presence of ANG II, a significant increase in HCO3- reabsorption was observed, expressed by a fall in acidification half time from a mean of 4.75 +/- 0.20 (n = 86) to 2.47 +/- 0.18 s (n = 32) in systemically infused rats or to 2.30 +/- 0.15 s (n = 35) in luminally perfused tubules and from 4.57 +/- 0.32 (n = 44) to 2.04 +/- 0.10 s (n = 50) during capillary perfusion. However, when ANG II was systemically infused or perfused in lumen or in peritubular capillaries, addition of ANF to lumen or capillaries by perfusion or systemic infusion abolished the effects observed with ANG II alone. These studies confirm that ANG II stimulates proximal HCO3- reabsorption and show that ANF alone does not affect this process, but impairs the stimulation caused by ANG II.