Interaction between adrenomedullin and angiotensin II in DNA synthesis and extracellular matrix accumulation in cultured rat kidney interstitial cells

Background. To investigate the role of adrenomedullin (AM) in the regulation of renal fibrosis, we assessed the effects of AM on angiotensin II (AT II)-induced cell proliferation and extracellular matrix (ECM) accumulation in cultured NRK 49F cells, a cell line derived from normal rat kidney fibroblasts. Methods. Northern blot analysis was performed, using cDNA probes against rat AM, human calcitonin-receptor-like receptor (CRLR), human receptor-activity-modifying protein 2 (RAMP 2), human collagen α-1 (I) (Col-I), human fibronectin (FN), and rat transforming growth factor (TGF)-β1. Polymerase chain reaction (PCR) analysis for CRLR was amplified for 35 cycles. Cell proliferation was determined by the measurement of ³H]thymidine incorporation. Results. We have shown that NRK 49F cells express AM and its receptor, which consists of a CRLR and RAMP 2. Rat AM significantly inhibited cell proliferation and mRNA expression of ECM in the absence and presence of AT II through an AM receptor, because calcitonin gene-related peptide (8-37) CGRP (8-37)], an antagonist to AM receptor, completely reversed these inhibitory actions. The inhibitory effects appeared to be mediated by a marked increase in intracellular cAMP. While AT II enhanced ECM accumulation by a process depending upon autocrine TGF-β1 secretion in NRK 49F cells, AM suppressed the induction of TGF-β1. Conclusions. The inhibitory action of AM on ECM accumulation may be caused by the suppression of TGF-β1. AM may play an important role in the inhibition of renal interstitial fibrosis under pathological conditions, through acting in an autocrine and/or paracrine fashion. Received: May 2, 2001 / Accepted: November 27, 2001