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J Lab Clin Med. 2000 Apr;135(4):353-9.
Angiotensin II-induced cardiomyocyte hypertrophy and cardiac fibrosis in stroke-prone spontaneously hypertensive rats.

Ikeda Y, Nakamura T, Takano H, Kimura H, Obata JE, Takeda S, Hata A, Shido K, Mochizuki S, Yoshida Y.

Department of Internal Medicine, Yamanashi Medical University, Japan.

Angiotensin-converting enzyme inhibitors (ACEIs) cause regression of hypertensive left ventricular hypertrophy (LVH) by reducing angiotensin II, increasing bradykinin, or both. The mechanisms of these cardioprotective effects remain controversial. The aims of this study were to determine whether the cardioprotective effects of ACEIs are mediated by reducing angiotensin II and whether ACEIs ameliorate the morphologic, physiologic, and biochemical changes in the hearts of stroke-prone spontaneously hypertensive rats (SHRSPs). Male SHRSPs were treated with hydralazine, captopril, or candesartan, an angiotensin II type 1 receptor (AT1R) antagonist, from age 12 to 24 weeks. We measured systolic blood pressure (SBP), left ventricular weight (LVW), left ventricular (LV) myocyte cross-sectional area (myocyte size), LV Interstitial collagen volume fraction (ICVF), perivascular collagen area/luminal area ratio (PVCA/LA), the medial area to luminal area ratio (MA/LA), the relative amount of V3 myosin heavy chain (MHCV3), and coronary reserve maximum (coronary flow max/ventricular weight (CFmax/VW)). These parameters were compared with those of untreated SHRSPs and Wistar-Kyoto rats (WKYs). SHRSPs exhibited decreased coronary reserve and LVH with an increase in myocyte size, PVCA/LA, MA/LA, and MHCV3 at 12 weeks of age. In addition to these changes, 24-week-old SHRSPs showed an increase in ICVF. The LVW, coronary reserve, myocyte size, PVCA/LA, ICVF, and MHCV3 of SHRSPs treated with captopril or candesartan all approached control values. In contrast, hydralazine decreased only ICVF. These results suggest that ACEIs regress LVH and normalize coronary reserve by modulating the effects of angiotensin II via AT1R on the induction of cardiomyocyte hypertrophy, perivascular fibrosis, and medial thickening of intramyocardial coronary arteries in SHRSPs. We concluded that these effects, in addition to the reduction of SBP, are important in causing the regression of LVH.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10779052&dopt=Abstract

physiology.unimelb.edu.au

OBJECTIVE: The objective of this study was to determine whether cardiac hypertrophy in hypertensive rats could be reduced and normalized by intermittent reduction of blood pressure, and to determine whether left ventricular hypertrophy was related to 24 h workload or peak blood pressure responses. METHODS: Hypertension was created by the application of a 0.20 mm clip to the left renal artery. Blood pressure response was monitored using a telemetry system (Data Science International). Blood pressure was reduced for varying periods of the day by giving different doses of captopril in the drinking water or by intra-peritoneal administration. Cardiac size was measured by weighing the ventricles and factoring by the body weight to obtain a cardiac index. RESULTS: Captopril 75 mg/kg per day and 25 mg/kg per day in the drinking water administered between 1800 and 2000 h lowered the 24 h blood pressure more than captopril 15 mg/kg per day or 5 mg/kg per day intra-peritoneally given at 0800 h. Captopril 75 mg/kg per day and captopril 15 mg/kg per day (intra-peritoneal) caused regression of cardiac hypertrophy whereas the other doses had no effect The best predictor of the cardiac hypertrophy response was the blood pressure between 0800 and 1200 h (i.e. the sleeping blood pressure). Twenty-four hour cardiac work did not correlate with the response. CONCLUSION: Cardiac hypertrophy can be reduced by intermittent treatment of elevated blood pressure. It is also caused by intermittent elevation of blood pressure. It appears that the crucial factor is when these alterations in blood pressure take place. An elevated blood pressure during the sleeping hours causes left ventricular hypertrophy, whereas a normal blood pressure during the sleeping hours allows reduction. It is suggested that acute wall stress is the signal to initiate the events that lead to cardiac hypertrophy but this only occurs if the hormonal milieu is appropriate.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10779096&dopt=Abstract

hotmail.com

The aims of this study were to examine the possible alterations occurring in the effects of kinins on isolated aortae of inbred control (CHF 148) and cardiomyopathic (CHF 146) hamsters of 150 - 175 and 350 - 375 days of age. Bradykinin (BK) and desArg(9)BK contracted isolated aortae (with or without endothelium) of hamsters of both strains and ages. After tissue equilibration (90 min), responses elicited by both kinin agonists were stable over the time of experiments. The patterns of isometric contractions of BK and desArg(9)BK were however found to be different; desArg(9)BK had a slower onset and a longer duration of action than BK. Potencies (pEC(50) values) of BK in all groups of hamsters were significantly increased by preincubating the tissues with captopril (10(-5) M). No differences in the pEC(50) values and the E(max) values for BK or desArg(9)BK were seen between isolated vessels from inbred control and cardiomyopathic hamsters. The myotropic effect of BK was inhibited by the selective non peptide antagonist, FR 173657 (pIC(50) 7.25+/-0.12 at the bradykinin B(2) receptor subtype (B(2) receptor)). Those of desArg(9)BK, at the bradykinin B(1) receptor subtype (B(1) receptor) were abolished by either R 715 (pIC(50) of 7. 55+/-0.05; alpha(E) = 0), Lys[Leu(8)]desArg(9)BK (pIC(50) of 7.21+/-0. 01; alpha(E) = 0.22) or [Leu(8)]desArg(9)BK (pIC(50) of 7.25+/-0.02; alpha(E) = 0.18). FR 173657 had no agonistic activity, exerted a non competitive type of antagonism and was poorly reversible (lasting more than 5 h) from B(2) receptor. In vivo, FR 173657 (given per os at 1 and 5 mg kg(-1), 1 h before the experiment) antagonized the acute hypotensive effect of BK in anaesthetized hamsters. It is concluded that aging and/or the presence of a congenital cardiovascular disorder in hamsters are not associated with changes in the in vitro aortic responses to either BK or desArg(9)BK.

online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10780969&dopt=Abstract













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