AT ₁ Receptor Blockade Reduces Cardiac Calcineurin Activity in Hypertensive Rats

Abstract

Abstract-The possible role of calcineurin in the attenuation of cardiac hypertrophy and fibrosis by blockade of the angiotensin II type 1 (AT 1 ) receptor was investigated in Dahl salt-sensitive (DS) rats. The effect of the calcineurin inhibitor FK506 was also studied. DS rats progressively developed severe hypertension when fed a diet containing 8% NaCl from 7 weeks of age. In addition, marked cardiac hypertrophy and fibrosis were apparent and the activity of calcineurin and its mRNA expression in the myocardium was increased in these animals at 12 weeks in comparison with age-matched Dahl salt-resistant rats. The abundance of angiotensin-converting enzyme (ACE) and transforming growth factor (TGF)-␤1 mRNAs was also increased in the hearts of DS rats at 12 weeks. Treatment of DS rats with a non-antihypertensive dose of the selective AT 1 receptor blocker candesartan (1 mg/kg per day) or FK506 (0.1 mg/kg per day) from 7 to 12 weeks attenuated both calcineurin activity and its mRNA expression in the heart, as well as the development of cardiac hypertrophy and fibrosis, without affecting cardiac function. There are at least 2 isoforms for Ang II receptors, which are designated as AT 1 and AT 2 , and the AT 1 receptor is further subdivided into AT 1A and AT 1B . It is generally accepted that most of the traditional Ang II functions in the cardiovascular system are attributable to the AT 1 receptor. 3 Angiotensin-converting enzyme (ACE) inhibitors or AT 1 receptor blockers induce the regression or prevent the development of left ventricular (LV) hypertrophy, both in animal models 4 -6 and in hypertensive patients. 7,8 However, it has proved difficult to determine whether the antagonistic effects of ACE inhibitors and AT 1 receptor blockers on Ang II-induced growth promotion or the concomitant systemic hemodynamic effects of these agents underlie their beneficial action with regard to this condition. A non-antihypertensive dose of an ACE inhibitor was shown to reverse LV hypertrophy in aortic banded rats, 9,10 and the antihypertrophic effect of an AT 1 receptor blocker was shown to be greater than that of hydralazine, despite the greater antihypertensive effect of hydralazine, in spontaneously hypertensive rats. 6 These observations suggest that blood pressure reduction alone is not sufficient to prevent target organ damage and that the additional control of local or neurohumoral factors might also be required.An intracellular signaling pathway that includes the Ca 2ϩ -dependent protein phosphatase calcineurin has been shown to underlie cardiac hypertrophy. 11 Calcineurin has also been shown to play a key role in the development of pressure overload-induced cardiac hypertrophy. 12,13 A recent study suggested that calcineurin is involved in the development of cardiac hypertrophy induced by mineralocorticoid excess. 14 Furthermore, treatment of cultured cardiac myocytes with Ang II or phenylephrine results in activation of calcineurin. 15 However, the effect of the cardiac renin-angiotensin system (RAS) on calcineurin ...

Mechanism underlying the efficacy of combination therapy with losartan and hydrochlorothiazide in rats with salt-sensitive hypertension

“…However, myocardial expression of the AT 1A receptor gene was not altered in LVH rats, consistent with our previous results. 22 LOS induced only a moderate antihypertensive effect in this study, but it strongly inhibited ACE and AT 1A receptor gene expression in the heart, consistent with the cardioprotective effects of ARBs. In contrast, HCTZ suppressed cardiac ACE and AT 1A receptor gene expression to the same extent as did LOS, but its antihypertensive effect was greater than that of LOS.…”

“…25 In this study, LV hypertrophy and fibrosis were markedly attenuated by LOS in the presence of a moderate reduction in blood pressure, consistent with our previous results and those of others. 10,22,38 Thiazide-like diuretics have been the cornerstone of hypertension treatment for several years. Data from the ALLHAT trial showed that adequate blood-pressure reduction induced by thiazide-like diuretics was associated with fewer cardiovascular events including stroke and heart failure than was treatment with an ACE inhibitor 12 However, the cardiac effects of thiazide diuretics remain to be elucidated.…”

“…In this study, the systemic RAAS was suppressed by salt loading, whereas the cardiac RAS was activated, as shown by the upregulation of ACE gene expression apparent in the heart of rats in the LVH group, consistent with our previous results. 22 This increase in cardiac ACE gene expression may have contributed to an increase in angiotensin II-mediated signaling in the heart. Expression of the AT 1 receptor has been shown to be upregulated in several models of cardiac hypertrophy, 39 although the functional relevance of this change was not clear.…”

“…21 Histology LV tissue was fixed with ice-cold 4% paraformaldehyde for 48-72 h, embedded in paraffin wax and processed for histology as described. 22 In brief, transverse sections (thickness, 3 mm) were stained either with hematoxylin-eosin for routine histological examination or with Azan-Mallory solution for evaluation of the extent of fibrosis. All image analysis was carried out with NIH Scion Image software (Scion Corp., Frederick, MD, USA).…”

“…Portions of the RNA (2 mg) were subjected to reverse transcription (RT) with the use of random primers (Invitrogen, Carlsbad, CA, USA) and MuLV Reverse Transcriptase (Applied Biosystems, Foster City, CA, USA). The resulting complementary DNA was subjected to real-time PCR analysis with the use of a Prism 7700 Sequence Detector (Perkin-Elmer, Waltham, MA, USA), as previously described, 23 and with primers and TaqMan probes specific for atrial natriuretic peptide (ANP), 22 brain natriuretic peptide (BNP), 22 collagen type I 24 or type III, 24 angiotensin-converting enzyme (ACE), 22 the AT 1A 22 or AT 2 (5¢-CTGGCTGTGGCTGACTTACTC-3¢, 5¢-TTTGC ACATCACAGGTCCAAAG-3¢, and 5¢-TTGGCAACCCTTCCTCTCTGGGCA-3¢ as the forward primer, reverse primer and TaqMan probe, respectively; GenBank accession no. NM_022456) receptor, transforming growth factorb1 (TGF-b1) 22 or connective tissue growth factor (CTGF).…”