Although studies suggest that endothelin (ET) meditates vasoconstriction associated with post-ischemic acute renal failure (ARF), the effect of ischemia on endothelin receptors is equivocal. In the current study, the left renal artery in Sprague-Dawley rats was occluded for 60 min to induce ARF. Animals were allowed to recover and whole kidneys were removed 24 h later to prepare membranes for binding studies. Binding studies indicate that the left ischemic kidney displayed more [251I]ET-1 binding than the non-ischemic right kidney. Values of Bmaxand KDwere 159±33 fmol/mg and 545±137 pM vs. 272±35 fmol/mg of protein and 638±120 pM for right and left kidneys, respectively (n = 5). Both right and left kidneys from sham-operated rats exhibit similar B., and KD values (126±17 fmol/mg and 365±36 pM vs. 152±20 fmol/mg and 472±48 pM, n = 4). Similar results were obtained for ET-3 binding. No significant difference was observed for tissue concentrations of ET between the right and left kidneys. Although the wet weight was not significantly different, the protein content of ischemic kidneys were 33% less than that of non-ischemic kidneys. These results suggest that ET receptors may be up-regulated in post-ischemic kidneys. Alternatively, ET receptors may be expressed in regions of the kidney that are less susceptible to ischemia-induced tissue damage.