Altered gene expression of adrenomedullin and its receptor system and molecular forms of tissue adrenomedullin in left ventricular hypertrophy induced by malignant hypertension Kazuyoshi Tadokoro a , Toshio Nishikimi a, * , Yosuke Mori a , Xin Wang a , Kazumi Akimoto b , Hiroaki Matsuoka a a Department of Hypertension and Cardiorenal Medicine, Dokkyo University School of Medicine, Mibu, Tochigi 321-0293, Japan b Laboratory of Molecular and Cellular Biology, Dokkyo University School of Medicine, Mibu, Tochigi 321-0293, Japan Received 12 April 2002; accepted 29 July 2002 Abstract To investigate the pathophysiological role of adrenomedullin (AM) in left ventricular hypertrophy (LVH) in hypertension, we measured the plasma level, left ventricle (LV) tissue level, and mRNA abundance of AM and the mRNA abundance of the AM receptor system in the LV. We also analyzed the molecular forms of AM in the plasma and LV tissue and investigated the relationships between AM and the degree of LVH. We studied the following three groups: control Wistar Kyoto rats (WKY), control spontaneously hypertensive rats (SHR), and deoxycorticosterone acetate (DOCA)-salt SHR (D-SHR). We measured AM-mature, active form, and AM-total (active form + inactive form) in plasma and the LV by a newly developed immunoradiometric assay. Gene expression of AM was measured by Northern blot analysis and gene expression of AM receptor system components, such as calcitonin receptor-like receptor (CRLR), receptor activity modifying protein 2 (RAMP2), and RAMP3 was measured by the reverse transcription polymerase chain reaction method. After 3 weeks of DOCA treatment, D- SHR was characterized by higher blood pressure, LV weight, and plasma atrial natriuretic peptide levels compared with those in the other two groups. Plasma AM-mature and AM-total levels were significantly higher in D-SHR than in the other two groups, whereas there were no significant differences in the AM-mature/AM-total ratio among the three groups. On the other hand, LV tissue AM-mature and AM-total levels were also significantly higher in D-SHR than in the other two groups, and the AM-mature/AM-total ratio was significantly higher in LV tissues than in plasma. Furthermore, the LV tissue AM-mature/AM-total ratio was significantly higher in D-SHR compared with the other two groups. The LV tissue AM-mature/AM-total ratio was significantly correlated with LV weight/body weight (r = 0.92, p < 0.001). The gene expression levels of AM, CRLR, RAMP2, and RAMP3 in the LV were significantly higher in D-SHR than in the other two groups. These results suggest that the AM amidating enzyme activity, ligand, and receptor system are all upregulated in the LV hypertrophy in this malignant hypertensive rat model. Considering that AM serves as a local antihypertrophic autocrine and/or paracrine factor, the induction of AM system observed here may modulate the pathophysiology of LV hypertrophy in certain forms of malignant hypertension. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Adrenomedullin; Hypertension; Left ventricular hypertrophy 1. Introduction Adrenomedullin (AM) is a 52-amino-acid novel vaso- dilatory peptide that was originally discovered in human pheochromocytoma tissue [1]. AM is widely distributed in various tissues and organs, including the heart [2]. Subse- quent studies have demonstrated that the AM gene and specific binding sites for the AM peptide are highly expressed in the heart [3]. The considerable coincidence between the expression of the AM peptide and mRNA, and the expression of AM receptors in the heart suggests that the AM peptide may play a role in the regulation of cardiac hypertrophy and cardiac function as an autocrine and/or a paracrine factor. Indeed, we and other groups demonstrated that cardiac myocytes and fibroblasts produce and secrete AM, and AM inhibits cardiac hypertrophy in myocytes and collagen syn- thesis in cardiac fibroblasts, possibly via a cAMP signaling 0167-0115/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-0115(03)00024-7 * Corresponding author. Tel.: +81-282-87-2149; fax: +81-282-86- 1596. E-mail address: nishikim@dokkyomed.ac.jp (T. Nishikimi). www.elsevier.com/locate/regpep Regulatory Peptides 112 (2003) 71 – 78