Kouichi Tamura

The tissue renin–angiotensin system and extracellular matrix are involved in the cardiovascular hypertrophy and remodeling induced by hypertension. In this study, we examined the gene expression of the tissue renin–angiotensin system and fibronectin in inbred Dahl Iwai salt-sensitive and salt-resistant rats. Eight pairs of 6-week-old male Dahl Iwai salt-sensitive and salt-resistant rats were fed either a low- or high-salt diet (0.3% or 8% NaCl, respectively) for 4 weeks. Activities of the circulating renin–angiotensin system were measured by radioimmunoassay and the gene expression of tissue angiotensinogen, the angiotensin II type 1 receptor (AT1) and fibronectin were analyzed by Northern blot analysis. Salt loading significantly increased blood pressure and produced cardiovascular hypertrophy and nephrosclerosis in the salt-sensitive rats. Activities of the circulating renin–angiotensin system were lower in salt-sensitive rats than in salt-resistant rats fed the low-salt diet, and salt loading lowered these activities in salt-resistant rats but not in salt-sensitive rats. In salt-resistant rats, salt loading increased renal, cardiac and aortic angiotensinogen, AT1 and fibronectin messenger (m)RNA expression except for aortic fibronectin mRNA expression. In contrast, in the salt-sensitive rats, salt loading stimulated the expression of cardiac fibronectin and aortic angiotensinogen, AT1 and fibronectin mRNAs. Furthermore, the cardiac and aortic fibronectin mRNA levels in salt-sensitive rats were higher than those in salt-resistant rats when both strains were fed the high-salt diet. These results demonstrate that the expression of tissue angiotensinogen, AT1 and fibronectin mRNAs is regulated differently in Dahl Iwai salt-sensitive and salt-resistant rats, and indicate that salt-mediated hypertension activates the cardiac fibronectin gene independently of the tissue renin–angiotensin system and stimulates the aortic fibronectin gene with activation of the tissue renin–angiotensin system.

—This study examined expression of renin-angiotensin system (RAS) component mRNAs in angiotensinogen gene knockout (Atg−/−) mice. Wild-type (Atg+/+) andAtg−/− mice were fed a normal-salt (0.3% NaCl) or high-salt (4% NaCl) diet for 2 weeks. Angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensin II type 1a receptor (AT_1A), and angiotensin II type 2 receptor (AT₂) mRNA levels were measured by Northern blot analysis. InAtg+/+ mice, activities of circulating RAS and renal angiotensinogen mRNA level were decreased by salt loading, whereas levels of renal and cardiac ACE; renal, brain, and cardiac AT_1A; and brain and cardiac AT₂mRNA were increased by salt loading. Although activities of circulating RAS were not detected inAtg−/− mice, salt loading increased blood pressure inAtg−/− mice. InAtg−/− mice, renal renin mRNA level was decreased by salt loading; in contrast, salt loading increased renal AT_1Aand cardiac AT₂mRNA levels inAtg−/− mice, and these activated levels inAtg−/− mice were higher than those inAtg+/+ mice fed the high-salt diet. Thus, expression of each component of the RAS is regulated in a tissue-specific manner that is distinct from other components of systemic and local RAS and that appears to be mediated by a mechanism other than changes in the circulating or tissue levels of angiotensin peptides.