AJP - Renal Physiology, Vol 239, Issue 3 228-F232, Copyright © 1980 by American Physiological Society
Distal tubular function in superficial rat tubules during volume expansion
J. Diezi, M. Nenniger and G. Giebisch
Free-flow micropuncture experiments were carried out on superficial late
proximal and distal tubules during hydropenic conditions and during
extracellular volume expansion. Fluid collected from tubules was analyzed
for inulin and sodium. During volume expansion, renal perfusion pressure to
one kidney was reduced so that the increase in distal sodium and fluid
delivery that normally occurs after saline loading was prevented. Although
urinary sodium excretion remained significantly elevated in such kidneys,
the rate of sodium reabsorption along the distal tubules was not different
from that occurring under nondiuretic conditions. It is concluded that
those factors that reduce net sodium transport in the proximal tubule
during extracellular volume expansion do not act on superficial distal
tubules. Additional factors beyond the distal tubule contribute to
increased sodium excretion and can be shown to be activated even when
delivery of fluid and sodium out of superficial distal tubules is normal.
