Chronic administration of losartan plus hydrochlorothiazide improves vascular status in young cardiomyopathic hamsters

δ-Sarcoglycan-deficient muscular dystrophy: from discovery to therapeutic approaches

Mutations in the δ-sarcoglycan gene cause limb-girdle muscular dystrophy 2F (LGMD2F), an autosomal recessive disease that causes progressive weakness and wasting of the proximal limb muscles and often has cardiac involvement. Here we review the clinical implications of LGMD2F and discuss the current understanding of the putative mechanisms underlying its pathogenesis. Preclinical research has benefited enormously from various animal models of δ-sarcoglycan deficiency, which have helped researchers to explore therapeutic approaches for both muscular dystrophy and cardiomyopathy.

Enalapril and Losartan Are More Effective Than Carvedilol in Preventing Dilated Cardiomyopathy in the Syrian Cardiomyopathic Hamster

To assess the role of the renin—angiotensin (RAS) and adrenergic systems in the development and progression of dilated cardiomyopathy in the Syrian cardiomyopathic hamster (SCH), echocardiographic parameters were evaluated in 6-month-old animals after 5 months of treatment with enalapril (25 mg/kg/day) plus losartan (10 mg/kg/day), or with carvedilol (1 mg/kg/day). Cardiac output indexes (COI) increased by 53% after RAS blockade and by 20% after β-blockade in SCH. Moreover, LVEDV and LVESV decreased 30% and 62%, respectively ( P < .05) during RAS blockade, whereas ejection fraction (EF) increased by 48%. By contrast, carvedilol reduced LVESV by only 28% ( P < .05) and increased EF by only 15% ( P < .05). These results suggest that RAS activation plays a critical role in the development of cardiac dysfunction in SCH and that suppression of RAS may be more effective than β-blockade in retarding the development of cardiomyopathy in SCH. Owing to timing (pre—heart failure stage) and to the single dose protocol, the implications of this study for human subjects remain to be clarified.

Determination of hydrochlorothiazide in human plasma by liquid chromatography/tandem mass spectrometry

In this study, a fast and sensitive liquid chromatography/tandem mass spectrometry method for determination of hydrochlorothiazide in human plasma was developed and validated. The analyte and irbesartan, used as the internal standard, were precipitated and extracted from plasma using methanol. Analysis was performed on a Phenomenex Kromasil C(8) column with water and methanol (27:73, v/v) as the mobile phase. Linearity was assessed from 0.78 to 200 ng/mL in plasma. The analytical method proved to be applicable in a pharmacokinetic study after oral administration of 12 mg hydrochlorothiazide tablets to 20 healthy volunteers.

Chronic administration of carvedilol improves cardiac function in 6-month-old Syrian cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been linked to activation of the renin-angiotensin and sympathetic systems. In recent years, beta-blockers have been shown to improve the status of HF patients, although the precise mechanisms remain unclear. The present study evaluates the effect of beta-blockade with carvedilol (1 mg/kg/day) on cardiovascular function in 2- and 6-month-old cardiomyopathic hamsters (SCH) after 1-month and 5-month treatment periods with the drug, respectively. Age-matched golden hamsters were used as controls (CT). Systolic blood pressure (SBP) and echocardiographic studies were evaluated. The latter studies included left ventricular end-systolic (LVESV) and end-diastolic (LVEDV) volumes, ejection fraction (EF), cardiac output index (COI), heart rate (HR), and left ventricular posterior wall thickness (LVPWT). In 2-month-old SCH, carvedilol administration during a 1-month period reduced SBP from 107.59 +/- 3.49 to 77.26 +/- 3.49 mm Hg (n = 5, p < 0.05). At this stage, cardiac parameters in SCH were similar to those of controls and were not affected by carvedilol administration. In 6-month-old SCH, 5-month administration of carvedilol decreased SBP from 102.16 +/- 3.61 to 90.60 +/- 2.80 mm Hg (n = 5, p < 0.05), HR from 363 +/- 14 to 324 +/- 14 bpm (n = 5, p < 0.05), and LVESV from 0.18 +/- 0.01 to 0.13 +/- 0.01 ml/100 g BW (n = 5, p < 0.05), and increased EF and COI by 14 and 23%, respectively (n = 5, p < 0.05). The drug did not modify LVEDV or LVPWT. These results reveal that carvedilol significantly improves cardiac function in 6-month-old cardiomyopathic hamsters, but it does not prevent ventricular dilatation. Improved cardiac function appears to be secondary to decreased total peripheral resistance, due mainly to the vasodilator properties of the drug. Thus, overactivation of the sympathetic system is not likely to be a determining factor in the etiology of dilated cardiomyopathy in this animal model.

Chronic blockade of angiotensin II AT1-receptors increased cell-to-cell communication, reduced fibrosis and improved impulse propagation in the failing heart

INTRODUCTION

The influence of chronic administration of losartan on gap junction conductance (gj), conduction velocity and interstitial fibrosis was investigated in the failing heart of 4-month-old cardiomyopathic hamsters (TO-2). After two months of administration of losartan (25 mg/kg/day/po) the number of cell pairs showing very low values of gj (28 nS) was significantly reduced whereas the group of cell pairs with larger values of gj (18-45 nS) was significantly increased. The conduction velocity measured with intracellular microelectrodes in the wall of the left ventricle was enhanced from 38+2.3 cm/s (n=25) (control) to 49+2 cm/s (n=24) (p<0.05) after losartan administration. Moreover, the number of ventricular fibres showing non-propagated action potentials was significantly decreased (p<0.05) by losartan. The % area of interstitial fibrosis measured in the wall of the left ventricle was reduced from 22+1.4% (n=18) to 14+1.3% (n=18) (p<0.05) after losartan administration.

CONCLUSION

Chronic blockade of angiotensin II type 1 receptors increased gj in the failing heart. Moreover, the conduction velocity was enhanced in part by the increase of gj and in part by the decrease of interstitial fibrosis and structural remodelling.

ETBreceptor dependent alteration in aortic responses to ET-1 in the cardiomyopathic hamsterThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

The aim of this study was to verify whether an alteration in the aortic endothelin-1 (ET-1) response takes place in UM-X7.1 cardiomyopathic hamsters. Our results showed that ET-1 (10−12– 10−5 mol/L) induces dose-dependent sustained increases in tension in the intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters. The EC50values of ET-1 of both intact and endothelium denuded aortas of normal hamsters were similar (2.2 × 10−9 mol/L and 1.8 × 10−9 mol/L, respectively). However, in cardiomyopathic hamsters, the EC50of ET-1 in intact aortas was higher (1.5 × 10−8 mol/L) than that of the endothelium denuded preparations (2.7 × 10−9 mol/L). The EC50of ET-1 in normal and cardiomyopathic hamster denuded aortas were similar. However, the EC50of ET-1 in intact aortas of cardiomyopathic hamster was higher (1.5 × 10−8 mol/L) than that of normal hamsters (2.2 × 10−9 mol/L). Pre-treatment with the ETAreceptor antagonist ABT-627 (10−5 mol/L) of intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters significantly prevented ET-1 (10−7 mol/L) from inducing an increase in tension. Pre-treatment with the ETBreceptor antagonist A-192621 (10−5 mol/L) had no effect on the ET-1-induced increase in tension in endothelium denuded aortas of both normal and cardiomyopathic hamsters, as well as in intact preparations of normal animals. However, blockade of the ETBreceptors in intact aortas of cardiomyopathic hamsters significantly (p < 0.001) potentiated the ET-1-induced increase in tension. In summary, an attenuation of the contraction response to ET-1 was found in UM-X7.1 cardiomyopathic hamsters when compared with normal age-matched hamsters. This alteration of the ET-1 effect in the aortas of cardiomyopathic hamsters seems to be dependent on the presence of the endothelium and could be due, in part, to an increase in the contribution of endothelial ETBreceptors to relaxation, which in turn acts as a physiological depressor of ET-1 vasoconstriction. Our results suggest that an increase in the endothelium ETBreceptor density may play a role in the development of hypotension in UM-X7.1 cardiomyopathic hamsters.

Increased vascular angiotensin II binding capacity and ET-1 release in young cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been associated with multiple systemic and vascular alterations. Previous reports from our laboratory showed that in 2-month-old Bio-To2 Syrian cardiomyopathic hamsters (SCH) that have not yet developed the clinical manifestations of HF, the vascular contractility induced by 0.1 microM angiotensin II was approximately 35% greater than in control animals. This finding was observed concomitantly with an increased aortic ACE activity. To further evaluate the mechanisms underlying angiotensin II-enhanced vascular contraction, concentration-response curves for angiotensin II (0.01 nM-10 microM) were constructed before and after the addition of prazosin (alpha-1 blocker), NS-398 (selective COX-2 blocker) and BQ-123 (ET-1A-receptor antagonist) in aortic rings from 2-month-old SCH. The binding capacity and affinity of the AT-1 receptors were also evaluated in aortic homogenates using 125I-angiotensin II. Age-matched golden hamsters were used as controls (CT). Our results indicate that incubation with either 10 microM prazosin or 10 microM NS-398 did not modify EC50 or Emax values for angiotensin II indicating that norepinephrine and prostaglandins are not involved in the enhanced contractile action of angiotensin II. However, 10 microM BQ-123 reduced by 40% the contraction induced by 1.0 microM angiotensin II (from 1.05+/-0.04 to 0.6475+/-0.06 g/mg tissue, n = 5, P < 0.05), suggesting that in cardiomyopathic hamsters, the action of angiotensin II is mediated in part by ET-1. At lower angiotensin II concentration (0.1 microM), the ET-1-dependent contraction decreases to 29%. In addition, although dissociation constants for labeled angiotensin II were found to be similar in the aorta of SCH and control animals (K(D): CT = 7.8 nM and SCH = 5.1 nM), 125I-angiotensin II binding capacity was about 2-fold greater in SCH than in controls (Bmax: SCH = 1113 and CT = 605 fmol/mg protein). Altogether these results suggest that in 2-month-old SCH the enhanced response of angiotensin II in the vasculature is mediated both by an increased binding capacity for the hormone and facilitation of the ET-1 action.

Angiotensin II-dependent vascular alterations in young cardiomyopathic hamsters: Role for oxidative stress

Recent studies indicate the presence of vascular alterations in 2-month-old Syrian cardiomyopathic hamsters (SCH). These alterations include enhanced angiotensin-converting enzyme (ACE) activity in the aorta, increased contractile response to angiotensin II and impaired vasorelaxation to acetylcholine in norepinephrine-precontracted aortic rings. The mechanisms leading to these vascular alterations are not known nor has their relationship to the cardiac abnormalities been established. We assessed the status of the cardiovascular system of 2-month-old hamsters first to establish if the observed vascular alterations are secondary to cardiac dysfunction, and second to examine the role of oxidative stress in the etiology of vascular dysfunction. Cardiac function parameters evaluated by echocardiography included stroke volume (SV), left ventricular end-diastolic volume (LVEDV), left ventricular fractional shortening (LVFS), ejection fraction (EF), cardiac output index (COI), heart rate (HR) and left ventricular posterior wall thickness (LVPWT). In addition, heart/body weight (heart/BW) ratios and systolic blood pressure were determined in normal hamsters and SCH. Our results indicated that systolic blood pressure increased 56% in SCH when compared to control animals (P<0.05). The increased blood pressure coexisted with normal COI, SV, LVEDV, LVPWT, LVFS, EF, HR and heart/BW ratios. NAD(P)H oxidase activity increased 77% in SCH compared to control animals (P<0.02). The increased oxidase activity was abolished by pre-treatment of animals with the angiotensin II type 1 receptor blocker losartan (25 mg/kg BW/day) for 10 days. Losartan also abolished the increased blood pressure observed at 2 months of age. The antioxidant N-acetylcysteine (NAC) abrogated the increased blood pressure when administered for 30 days to 1-month-old animals. Altogether, these findings suggest that the angiotensin II-dependent vascular abnormalities present in young cardiomyopathic hamsters are associated with oxidative stress and precede the echocardiographic abnormalities characteristic of heart failure.