EFFECTS OF REDUCED RENAL PERFUSION-PRESSURE AND ACUTE VOLUME EXPANSION ON PROXIMAL TUBULE AND WHOLE KIDNEY ANGIOTENSIN-II CONTENT IN THE RAT

In previous studies high luminal concentrations of angiotensin II (Ang II) were found in rat proximal tubules. The physiological role of int raluminal Ang II remains to be established. In the present study, we i nvestigated whether the luminal angiotensin II concentration in the pr oximal tubules ([Ang II](prox)) can be modulated. Micropuncture studie s were performed in control rats (C, N = 8) and rats subjected to acut e volume expansion (VE. N = 8) or reduced renal perfusion pressure (RR P. N = 7). Changes in [Ang II](prox) were compared to changes in whole kidney Ang II content ([Ang II](kidney)) and the plasma concentration ([Ang II](plasma)). In C rats, [Ang II](prox) was 460 +/- 48 pmol/lit er (10 to 20 times lower than hitherto reported), while [Ang II](kidne y) and [Ang II](plasma) were 369 +/- 81 pmol/kg and 90 +/- 29 pmol/lit er, respectively. In agreement with previous data, VE failed to suppre ss [Ang II](prox) (674 +/- 132 pmol/liter), while at the same time [An g II](kidney) (42 +/- 10 pmol/kg) and [Ang II](plasma) (12 +/- 3 pmol/ liter) were markedly suppressed. This points to dissociated regulation of [Ang II] in thr renal luminal compartment on the one hand and the extraluminal renal and systemic plasma compartments on thr: other hand . During RRP. [Ang II](prox) increased significantly to 1675 +/- 465 p mol/liter. No dissociation between the three compartments was observed in this situation, as [Ang II](kidney) (969 +/- 85 pmol/kg) and [Ang II](plasma) (245 +/- 72 pmol/liter) increased in parallel. In summary, we confirm that Ang II is present in proximal tubules of rat kidneys at concentrations which exceed those in plasma. Its concentration coul d be modulated (similar to 3.5 increase) by reduction oi renal perfusi on pressure but not by acute volume expansion. In the latter condition , we observed a clear dissociation from Ang II generation in the extra luminal renal compartment, as whole kidney Ang II content was markedly suppressed.