Neutral endopeptidase (NEP, 24.11) is an ectoenzyme involved in the degradation of peptide hormones such as endothelin (ET), atrial natriuretic factor and enkephalins. The current study was designed to assess the involvement of NEP in ischemia-induced acute renal failure (ARF). In unilaterally nephrectomized Sprague-Dawley rats, the left renal artery was occluded for 30 min under pentobarbital anesthesia (40 mg/kg, i.p.) at 37 degree C. In addition to plasma creatinine levels, NEP activity was determined in renal cortical membranes at 0, 2, 5, and 24 h following reperfusion. Plasma creatinine levels significantly increased at 2, 5 and 24 h. There was a significant decrease in NEP activity as early as 2 h following reperfusion that was maintained up to 24 h (57.9 +/- 4%) with a concomitant loss of enzyme protein shown by Western analysis. Northern analysis of kidney cortical RNA, probed with an NEP cDNA, showed a 45% decrease in NEP mRNA level by the end of the ischemic period and decreased further during reperfusion. Thus, decrease in NEP mRNA levels preceded the changes in protein level, enzyme activity and plasma creatinine levels. These data, along with the reported increase in the tissue level of ET in kidney cortex, and the beneficial effect of ET antibody as well as ET receptor antagonist in ARF, suggest that down regulation of NEP, one of the mechanisms leading to increased tissue level of ET, may be a contributing factor to ARF.