Endothelin and Endothelin A/B Receptors Are Increased after Ischaemic Acute Renal Failure

Abstract

Background/Aims: Endothelin (ET) has been implicated as an indirect mediator of injury following acute renal ischaemia (ARI). The purpose of this study was to localize and quantitate ET and ET_A and ET_B receptors following ARI. Methods: A model of ARI, well characterized previously, was produced by 45 min occlusion of the renal pedicle of unilaterally nephrectomized female Sprague-Dawley rats. Animals were sacrificed 1, 2, 4, 8, 16, 32 and 64 days after ischaemia (n = 6). Corresponding control groups with unilateral nephrectomy but no ischaemia were sacrificed after 0, 8 and 64 days. Immunohistochemistry for ET-1, -2 and -3 was performed. Tissue ET levels were calculated by RIA (femtomoles per kidney). Receptor ligand binding studies for ET_A and ET_B receptors were performed by autoradiography on frozen kidney sections and quantitated by densitometry (relative optical density per square millimetre). Results: The concentration of tissue ET increased from 24 h after ischaemia and remained significantly increased for the duration of the study, reaching a maximum at 8 days. There was a small increase in the non-ischaemic 8-day control group, but this returned to basal levels by day 64. The increase in tissue ET 8 days after ischaemia was localized by immunohistochemistry to renal medullary interstitial cells, damaged tubules at the corticomedullary junction and peritubular capillaries surrounding these damaged tubules. Increases in cortical ET_A and ET_B receptors were evident 24 h after ischaemia and were maximal 8 days after ischaemia, before returning to basal levels at 16 days. After a small increase 24 h after ischaemia, medullary ET_A receptors decreased on day 4 before returning to basal levels on day 8 after ischaemia. Medullary ET_B receptors, however, decreased on day 4 after ischaemia and remained low throughout the duration of the study. Conclusion: The previously reported amelioration of pathological changes resulting from the use of ET receptor antagonists after ARI may be related to the quantitative and qualitative changes in tissue ET and ET receptors observed in this study.