Antifibrotic activity of an inhibitor of group IIA secretory phospholipase A(2) in young spontaneously hypertensive rats

The development of fibrosis in the chronically hypertensive heart is associated with infiltration of inflammatory cells and cardiac hypertrophy. In this study, an inhibitor of the proinflammatory enzyme, group IIA human secretory phospholipase A(2) (sPLA(2)-IIA), has been found to prevent collagen deposition as an important component of cardiovascular remodeling in a rat model of developing chronic hypertension. Daily treatment of young male spontaneously hypertensive rats (SHR) with an sPLA2-IIA inhibitor (KH064, 5-(4-benzyloxyphenyl)-4S-(phenyl-heptanoylamino)-pentanoic acid, 5 mg/kg/day p.o.) prevented increases in the content of perivascular,(SHR 20.6 +/- 0.9%, n = 5; SHR+KH064 14.0 +/- 1.2%, n = 5) and interstitial (SHR 7.9 +/- 0.3%, n = 6; SHR+KH064 5.4 +/- 0.7%, n = 6) collagen in the left ventricle of rat hearts, but did not affect numbers of infiltrating monocytes/macrophages, left ventricular hypertrophy (SHR 2.88 +/- 0.08, n = 12; SHR+KH064 3.09 +/- 0.08 mg/g body weight, n = 9), increased systolic blood pressure, or thoracic aortic responses. This selective antifibrotic activity suggests that sPLA2-IIA may have an important but specific role in cardiac fibrosis, and that its inhibitors could be useful in dissecting molecular pathways leading to fibrotic conditions.

Cosegregation analysis of natriuretic peptide genes and blood pressure in the spontaneously hypertensive rat

1. The natriuretic peptide precursor A (Nppa) and B (Nppb) genes are candidate genes for hypertension and cardiac hypertrophy in the spontaneously hypertensive rat (SHR). The purpose of the present study was to determine the role of the Nppa and Nppb genes in the development of hypertension in the SHR. 2. A cohort (n = 162) of F2 segregating intercross animals was established between strains of hypertensive SHR and normotensive Wistar-Kyoto rats. Blood pressure and heart weight were measured in each rat at 12-16 weeks of age. Rats were genotyped using 11 informative microsatellite markers, distributed in the vicinity of the Nppa marker on rat chromosome 5 including an Nppb marker. The phenotype values were compared with genotype using the computer package MAP-MAKER 3.0 (Whitehead Institute, Boston, MA, USA) to determine whether there was a link between the genetic variants of the natriuretic peptide family and blood pressure or cardiac hypertrophy. 3. A strong correlation was observed between the Nppa marker and blood pressure. A quantitative trait locus (QTL) for blood pressure on chromosome 5 was identified between the Nppa locus and the D5Mgh15 marker, less than 2 cM from the Nppa locus. The linkage score for the blood pressure QTL on chromosome 5 was 3.8 and the QTL accounted for 43% of the total variance of systolic blood pressure, 54% of diastolic blood pressure and 59% of mean blood pressure. No association was found between the Nppb gene and blood pressure. This is the first report of linkage between the Nppa marker and blood pressure in the rat. There was no correlation between the Nppa or Nppb genes or other markers in this region and either heart weight or left ventricular weight in F2 rats. 4. These findings suggest the existence of a blood pressure-dependent Nppa marker variant or a gene close to Nppa predisposing to spontaneous hypertension in the rat. It provides a strong foundation for further detailed genetic studies in congenic strains, which may help to narrow down the location of this gene and lead to positional cloning.

L-arginine attenuates cardiovascular impairment in DOCA-salt hypertensive rats

Nitric oxide (NO) is essential for normal function of the cardiovascular system. This study has determined whether chronic administration of L-arginine, the biological precursor of NO, attenuates the development of structural and functional changes in hearts and blood vessels of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Uninephrectomized rats treated with DOCA (25 mg every 4th day sc) and 1% NaCl in the drinking water for 4 wk were treated with L-arginine (5% in food, 3.4 +/- 0.3 g.kg body wt(-1).day(-1)). Changes in cardiovascular structure and function were determined by echocardiography, microelectrode studies, histology, and studies in isolated hearts and thoracic aortic rings. DOCA-salt hypertensive rats developed hypertension, left ventricular hypertrophy with increased left ventricular wall thickness and decreased ventricular internal diameter, increased inflammatory cell infiltration, increased ventricular interstitial and perivascular collagen deposition, increased passive diastolic stiffness, prolonged action potential duration, increased oxidative stress, and inability to increase purine efflux in response to an increased workload. L-Arginine markedly attenuated or prevented these changes and also normalized the reduced efficacy of norepinephrine and acetylcholine in isolated thoracic aortic rings of DOCA-salt hypertensive rats. This study suggests that a functional NO deficit in blood vessels and heart due to decreased NO synthase activity or increased release of reactive oxygen species such as superoxide may be a key change initiating many aspects of the cardiovascular impairment observed in DOCA-salt hypertensive rats. These changes can be prevented or attenuated by administration of L-arginine.

Improved cardiovascular function with aminoguanidine in DOCA-salt hypertensive rats

1 The ability of aminoguanidine (AG), an inhibitor of collagen crosslinking, to prevent changes in cardiac and vascular structure and function has been determined in the deoxycorticosterone acetate (DOCA)-salt hypertensive rat as a model of the cardiovascular remodelling observed in chronic human hypertension. 2 Uninephrectomized rats (UNX) administered DOCA (25 mg every fourth day s.c.) and 1% NaCl in drinking water for 28 days developed cardiovascular remodelling shown as systolic hypertension, left ventricular hypertrophy, increased thoracic aortic and left ventricular wall thickness, increased left ventricular inflammatory cell infiltration together with increased interstitial collagen and increased passive diastolic stiffness, impaired contractility, prolongation of the action potential duration and vascular dysfunction. 3 Treatment with AG (0.05-0.1% in drinking water; average 182 +/- 17 mg kg(-1) day(-1) in DOCA-salt rats) decreased blood pressure (DOCA-salt 176 +/- 4; + AG 144 +/- 5 mmHg; *P < 0.05 vs DOCA-salt), decreased left ventricular wet weights (DOCA-salt 3.17 +/- 0.07; + AG 2.66 +/- 0.08 mg g(-1) body wt*), reduced diastolic stiffness constant (DOCA-salt 30.1 +/- 1.2; + AG 24.3 +/- 1.2* (dimensionless)), improved cardiac contractility (DOCA-salt 1610 +/- 130; + AG 2370 +/- 100 mmHg s(-1)*) and vascular reactivity (3.4-fold increase in maximal contractile response to noradrenaline, 3.2-fold increase in maximal relaxation response to acetylcholine, twofold increase in maximal relaxation response to sodium nitroprusside) and prolonged the action potential duration at 50% repolarization without altering collagen content or inflammatory cell infiltration. 4 Thus, cardiovascular function in DOCA-salt hypertensive rats can be improved by AG independent of changes in collagen content. This suggests that collagen crosslinking is an important cause of cardiovascular dysfunction during cardiovascular remodelling in hypertension.

Rosuvastatin attenuates hypertension-induced cardiovascular remodeling without affecting blood pressure in DOCA-salt hypertensive rats

The pleiotropic effects of statins represent potential mechanisms for the treatment of end-organ damage in hypertension. This study has investigated the effects of rosuvastatin in a model of cardiovascular remodeling, the DOCA-salt hypertensive rat. Male Wistar rats weighing 300 to 330 g were uninephrectomized (UNX) or UNX and treated with DOCA (25 mg subcutaneously every fourth day) and 1% NaCl in the drinking water. Compared with UNX controls, DOCA-salt rats developed hypertension, cardiovascular hypertrophy, inflammation with perivascular and interstitial cardiac fibrosis, endothelial dysfunction, and prolongation of ventricular action potential duration at 28 days. Rosuvastatin-treated rats received 20mg/kg/d of the drug in 10% Tween 20 by oral gavage for 32 days commencing 4 days before uninephrectomy. UNX and DOCA-salt controls received vehicle only. Rosuvastatin therapy attenuated the development of cardiovascular hypertrophy, inflammation, fibrosis, and ventricular action potential prolongation, but did not modify hypertension or vascular dysfunction. We conclude that the pleiotropic effects of rosuvastatin include attenuation of aspects of cardiovascular remodeling in the DOCA-salt model of hypertension in rats without altering systolic blood pressure.

Perindopril, an angiotensin converting enzyme inhibitor, in pulmonary hypertensive rats: comparative effects on pulmonary vascular structure and function

1 Hypoxic pulmonary hypertension in rats (10% O-2, 4 weeks) is characterized by changes in pulmonary vascular structure and function. The effects of the angiotensin converting enzyme inhibitor perindopril (oral gavage, once daily for the 4 weeks of hypoxia) on these changes were examined. 2 Perindopril (30 mg kg(-1) d(-1)) caused an 18% reduction in pulmonary artery pressure in hypoxic rats. 3 Structural changes (remodelling) in hypoxic rats included increases in (i) critical closing pressure in isolated perfused lungs (remodelling of arteries (50 mu m 0.d.) and (ii) medial wall thickness of intralobar pulmonary arteries, assessed histologically (vessels 30-100 and 101-500 mu m o.d.). Perindopril 10 and 30 mg kg(-1) d(-1) attenuated remodelling in vessels less than or equal to 100 mu m (lungs and histology), 30 mg kg(-1) d(-1) was effective in vessels 101-500 mu m but neither dose prevented hypertrophy of main pulmonary artery. 3 mg kg(-1) d(-1) was without effect. 4 Perindopril (30 mg kg(-1) d(-1)) prevented the exaggerated hypoxic pulmonary vasoconstrictor response seen in perfused lungs from hypoxic rats but did not prevent any of the functional changes (i.e. the increased contractions to 5-HT, U46619 (thromboxane-mimetic) and K+ and diminished contractions to angiotensins I and II) seen in isolated intralobar or main pulmonary arteries. Acetylcholine responses were unaltered in hypoxic rats. 5 We conclude that, in hypoxic rats, altered pulmonary vascular function is largely independent of remodelling. Hence any drug that affects only remodelling is unlikely to restore pulmonary vascular function to normal and, like perindopril, may have only a modest effect on pulmonary artery pressure.

L-arginine improves cardiovascular function in DOCA-salt hypertensive rats

No abstract

S-Nitrosocaptopril: In vitro characterization of pulmonary vascular effects in rats

1 On rat isolated pulmonary arteries, vasorelaxation by S-nitrosocaptopril (SNOcap) was compared with S-nitrosoglutathione (GSNO) and nitroprusside, and inhibition by SNOcap of contractions to angiotensin I was compared with the angiotensin converting enzyme (ACE) inhibitor, captopril. 2 SNOcap was equipotent as a vasorelaxant on main (i.d. 2-3 mm) and intralobar (i.d. 600 mum)pulmonary arteries (pIC(50) values: 5.00 and 4.85, respectively). Vasorelaxant responses reached equilibrium rapidly (2-3 min). 3 Pulmonary vasorelaxant responses to SNOcap, like GSNO, were (i) partially inhibited by the soluble guanylate cyclase inhibitor, ODQ (1H-(1,2,4) oxadiazolo(4,3-a)-quinoxalin-1-one; 3 muM) whereas responses to nitroprusside were abolished and (ii) potentiated by hydroxocobalamin (HCOB; NO. free radical scavenger; 100 muM) whereas responses to nitroprusside were inhibited. 4 The relative potencies for pulmonary vasorelaxation compared with inhibition of platelet aggregation were: SNOcap 7: 1; GSNO 25: 1; nitroprusside > 2000:1. 5 SNOcap, like captopril, concentration-dependently and time-dependently increased the EC50 for angiotensin I but not angiotensin II. The dependence on incubation time was independent of the presence of tissue but differed for SNOcap and captopril. This difference reflected the slow dissociation of SNOcap and instability of captopril, and precluded a valid comparison of the potency of the two drugs. After prolonged incubation (greater than or equal to 5.6 h) SNOcap was more effective than captopril. 6 Thus, in pulmonary arteries SNOcap (i) possesses NO donor properties characteristic of S-nitrosothiols but different from nitroprusside and (ii) inhibits ACE at least as effectively as captopril. These properties suggest that SNOcap could be valuable in the treatment of pulmonary hypertension.

Increased calcium influx mediates increased cardiac stiffness in hyperthyroid rats

Cardiac remodeling (hypertrophy and fibrosis) and an increased left ventricular diastolic stiffness characterize models of hypertension such as the SHR and DOCA-salt hypertensive rats. By contrast, hyperthyroidism induces hypertrophy and hypertension, yet collagen expression and deposition is unchanged or decreased, whereas diastolic stiffness is increased. We determined the possible role of increased calcium influx in the development of increased diastolic stiffness in hyperthyroidism by administering verapamil (15 mg/[kg(.)d] orally) to rats given triiodothyronine (T-3) (0.5 mg/[kg.d] subcutaneously for 14 d). Administration of T3 significantly increased body temperature (control: 36.7 +/- 0.2 degrees C; T-3: 39.6 +/- 0.2 degrees C), left ventricular wet weight (control: 2.09 +/- 0.02 mg/kg; T-3 3.07 +/- 0.07 mg/kg), systolic blood pressure (control: 128 +/- 5 mmHg; T-3: 156 +/- 4 mmHg), and left ventricular diastolic stiffness (control: 20.6 +/- 2.0; T-3: 28.8 +/- 1.4). Collagen content of the left ventricle was unchanged. Contractile response to noradrenaline in thoracic aortic rings was reduced. Relaxation in response to acetylcholine (ACh) was also reduced in T-3-treated rats, whereas sodium nitroprusside response was unchanged. Verapamil treatment of hyperthyroid rats completely prevented the increased diastolic stiffness and systolic blood pressure while attenuating the increased body temperature and left ventricular weight; collagen content remained unchanged. ACh response in thoracic aortic rings was restored by verapamil. Thus, in hyperthyroid rats, an increased calcium influx is a potential mediator of the increased diastolic stiffness independent of changes in collagen.