Early blood pressure-independent cardiac changes in diabetic rats Daniel Landau, Chen Chayat 1 , Nili Zucker, Eli Golomb 2 , Channa Yagil 3 , Yoram Yagil 3 and Yael Segev 1 Department of Pediatrics A, Faculty of Health Sciences, Soroka University Medical Center, Ben Gurion University, PO Box 151, Beer Sheva 84101, Israel 1 Shraga Segal Department of Microbiology and Immunology, 2 Department of Pathology and 3 Laboratory for Molecular Medicine and Israeli Rat Genome Center, Faculty of Health Sciences, Ben Gurion University, Beer Sheva 84105, Israel (Correspondence should be addressed to D Landau; Email: ldaniel@bgu.ac.il) Abstract Cardiac remodeling is a key event in both diabetic and hypertensive heart diseases. In the present study, we investigated early myocardial changes in an animal model, the male Sabra rat model (SBH/y) of salt-induced hypertension-rendered diabetic with streptozotocin. Control non-diabetic (C), diabetic (D), and D or C rats made hypertensive by salt loading (DS or CS) were studied after 6 weeks. M-mode echocardiography revealed that left ventricular internal dimension during diastole and systole were significantly increased in D and DS, but not in C or CS. Concurrently, we found in D and DS an increase in cardiac b-myosin heavy chain, atrial natriuretic peptide, skeletal a-actin mRNA, type III collagen, and transforming growth factor-b. Myocardial angiotensin-converting enzyme (ACE) mRNA levels were increased while ACE2 mRNA levels were decreased in both D and DS groups. Cardiac angiotensin-1 (AT1) receptor protein levels were unchanged but the levels of phosphorylated (p) ERK and Jun-NH 2 -protein kinase (JNK) were increased in D and DS. In conclusion, we detected early cardiac changes in diabetic rats that were unrelated to hypertension. The increase in ACE, the decrease in ACE2, and the increase in cardiac pERK and pJNK suggest an increase in free angiotensin II and AT1R signaling in the diabetic myocardium as a possible mechanism contributing to cardiac remodeling in diabetes. Journal of Endocrinology (2008) 197, 75–83 Introduction Heart disease, particularly coronary artery disease, is a major cause of morbidity and mortality among patients with diabetes mellitus (DM). Another important cardiovascular problem in diabetic patients, as suggested by the Framingham study, is the development of heart failure which is due to an ill-defined cardiomyopathy, even in the absence of coronary artery disease (Galderisi et al. 1991). Preclinical evidence for the occurrence of diabetic heart disease has been demonstrated in the form of both diastolic and systolic dysfunction and of structural abnormalities (Marwick 2006). In asymptomatic diabetic patients, diastolic dysfunction appears to be, in fact, very common (Zabalgoitia et al. 2001). Since hypertension is commonly associated with diabetes, however, and since hypertension per se has also been identified as an important cause of heart failure, it is difficult to identify the relative importance in the development of heart failure with diabetes and hypertension as single contributing factors. An early phase in the development of heart failure is cardiac remodeling. Cardiac remodeling is thought to be an important aspect of disease progression in heart failure, regardless of cause (Cohn et al. 2000). It is manifested clinically by changes in cardiac size, shape, and function in response to cardiac injury or increased load. The role of the renin–angiotensin system in cardiac remodeling is exempli- fied by the fact that angiotensin-converting enzyme (ACE) inhibitors, which improve survival in patients with heart failure, can slow down and in some cases even reverse certain parameters of cardiac remodeling (Greenberg et al. 1995). Angiotensin II (AngII) effects through its specific receptor (mostly AT1R) may depend on its local production. Free AngII levels are determined by the rate of its synthesis, regulated mostly by ACE, and degradation. The newly discovered ACE2 enzyme plays a role in this process (Burrell et al. 2004). Cardiac remodeling in DM and hypertension has been less extensively investigated in comparison with post-myocardial infarction models. The aim of the present study was to investigate cardiac remodeling at the functional and gene expression level in an experimental model of DM. We studied cardiac gene expression and the activation of ‘fetal’ cardiac genes, which encode proteins involved in contraction, calcium handling, and metabolism (Marks 2003). Since hypertension is more commonly associated with diabetes in the clinical setting, we also tested the hypothesis that hypertension per se is an important contributor to the development of cardiac remodeling in DM. Materials and Methods Animals The study was performed in the salt-sensitive hypertensive male Sabra rat model. This model consists of two strains: the Sabra hypertension-prone (SBH/y) rats that remain normotensive when fed regular diet but become hypertensive when salt 75 Journal of Endocrinology (2008) 197, 75–83 DOI: 10.1677/JOE-08-0040 0022–0795/08/0197–075 q 2008 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology-journals.org