Down regulation of kidney neutral endopeptidase mRNA, protein and activityduring acute renal failure: Possible mechanism for ischemia-induced acute renal failure in rats?

Neutral endopeptidase (NEP, 24.11) is an ectoenzyme involved in the degrada tion 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 nephr ectomized Sprague-Dawley rats, the left renal artery was occluded for 30 mi n under pentobarbital anesthesia (40 mg/kg, i.p.) at 37 degrees C. In addit ion to plasma creatinine levels, NEP activity was determined in renal corti cal 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 d ecrease in NEP activity as early as 2 h following reperfusion that was main tained up to 24 h (57.9 +/- 4%) with a concomitant loss of enzyme protein s hown 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 i n NEP mRNA levels preceded the changes in protein level, enzyme activity an d 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 a ntibody as well as ET receptor antagonist in ARF, suggest that down regulat ion of NEP, one of the mechanisms leading to increased tissue level of ET, may be a contributing factor to ARF.