N-domain angiotensin-converting enzyme isoform expression in tissues of Wistar and spontaneously hypertensive rats

Background Angiotensin I-converting enzyme (ACE) is a protein containing two active sites, called N- and C-domains, according to their position in the protein. Aim The aim of the present study was to verify whether the expression of the N-domain ACEs detected in the urine of Wistar and spontaneously hypertensive (SHR) rats was restricted to the kidney. Methods Adrenal, aorta, heart, liver, lung, kidney and testicle tissue from Wistar rats and spontaneously hypertensive rats were homogenized in assay buffer and analyzed by gel filtration, Western blotting and radio-immunoassay. Results Two peaks (at 136 and 69 kDa) with ACE activity upon ZPhe-His-Leu were separated by gel filtration from homogenate tissues of Wistar rats, in contrast with the tissue from hypertensive rats, which showed ACE forms of 96 and 69 kDa. The bands detected by Western blotting for all studied tissue from Wistar and spontaneously hypertensive rats showed a correspondence with the two peaks containing ACE activity detected in the polyacrylamide gel slices. Angiotensin 11 levels were increased in hypertensive rat tissue when compared with Wistar rat tissues. In addition, captopril 3 mu mol/l inhibited the enzymic activity, where the K, was in the order of mmol/l and mu mol/l using hippuryl-His-Leu and Abz-Ser-Asp-Lys(Dnp)Pro-OH as substrates, respectively. All tissues from Wistar rats presented ACE with 136 kDa, similar to somatic ACE, and N-domain ACE with 69 kDa. In the same tissue of spontaneously hypertensive rats, 96 and 69 kDa N-domain ACEs were detected. Conclusions Our results demonstrated that N-domain ACEs were not exclusively produced in the kidney and excreted in the urine; they were expressed in all tissue studied, suggesting that these enzymes could influence local angiotensin 11 production, contributing to organ-specific regulation. J Hypertens 23:1869-1878 (c) 2005 Lippincott Williams & Wilkins.