Overexpression of endothelial ß3 -adrenergic receptor induces diastolic dysfunction in rats.

AIMS: Diastolic dysfunction is common in cardiovascular diseases, particularly in the case of heart failure with preserved ejection fraction. The challenge is to develop adequate animal models to envision human therapies in the future. It has been hypothesized that this diastolic dysfunction is linked to alterations in the nitric oxide (• NO) pathway. To investigate this issue further, we investigated the cardiac functions of a transgenic rat model (Tgß3 ) that overexpresses the human ß3 -adrenoceptor (hß3 -AR) in the endothelium with the underlying rationale that the • NO pathway should be stimulated in the endothelium. METHODS AND RESULTS: Transgenic rats (Tgß3 ) that express hß3 -AR under the control of intercellular adhesion molecule 2 promoter were developed for a specific expression in endothelial cells. Transcriptomic analyses were performed on left ventricular tissue from 45-week-old rats. Among all altered genes, we focus on • NO synthase expression and endothelial function with arterial reactivity and evaluation of • NO and O2 •- production. Cardiac function was characterized by echocardiography, invasive haemodynamic studies, and working heart studies. Transcriptome analyses illustrate that several key genes are regulated by the hß3 -AR overexpression. Overexpression of hß3 -AR leads to a reduction of Nos3 mRNA expression (-72%; P < 0.05) associated with a decrease in protein expression (-19%; P < 0.05). Concentration-dependent vasodilation to isoproterenol was significantly reduced in Tgß3 aorta (-10%; P < 0.05), while • NO and O2 •- production was increased. In the same time, Tgß3 rats display progressively increasing diastolic dysfunction with age, as shown by an increase in the E/A filing ratio [1.15 ± 0.01 (wild type, WT) vs. 1.33 ± 0.04 (Tgß3 ); P < 0.05] and in left ventricular end-diastolic pressure [5.57 ± 1.23 mmHg (WT) vs. 11.68 ± 1.11 mmHg (Tgß3 ); P < 0.05]. In isolated working hearts, diastolic stress using increasing preload levels led to a 20% decrease in aortic flow [55.4 ± 1.9 mL/min (WT) vs. 45.8 ± 2.5 mL/min (Tgß3 ); P < 0.05]. CONCLUSIONS: The Tgß3 rat model displays the expected increase in • NO production upon ageing and develops diastolic dysfunction. These findings provide a further link between endothelial and cardiac dysfunction. This rat model should be valuable for future preclinical evaluation of candidate drugs aimed at correcting diastolic dysfunction.

ß1-Adrenergic cardiac contractility is increased during early endotoxemic shock: Involvement of cyclooxygenases.

AIMS: Endothelial dysfunction is one of the earliest symptoms in septic patients and plays an important role in the cardiovascular alterations. However, the endothelial mechanisms involved in the impaired sympathetic regulation of the cardiovascular system are not clear. This study aimed to determine the role of the endocardial endothelium (EE) in the cardiac ß-adrenergic (ß-AR) remodeling at the early phase of endotoxemic shock. MAIN METHODS: Rats received either lipopolysaccharide (LPS) or saline (control) intravenously. Three hours later, ß-AR cardiac contractility was evaluated on papillary muscles with or without a functional EE. KEY FINDINGS: Isoproterenol-induced contractility was strongly increased in papillary muscles from LPS rats. A similar increase was observed with a ß1-AR stimulation, whereas ß2-AR and ß3-AR produced similar contractility in control and LPS treatments. The removal of the EE did not modify ß1-AR-induced contractility in controls, whereas it abolished the increased ß1-AR response in LPS-treated muscles. In LPS-treated papillary muscle, the increased ß1-AR-induced contractility was not modified by pretreatment with a NOS inhibitor or an endothelin receptor antagonist. Conversely, the increased ß1-AR-induced contractility was abolished by indomethacin, a non-selective cyclooxygenase (COX) inhibitor, as well as by selective inhibitors of COX1 and COX2. An early treatment with indomethacin improved the survival of LPS rat. SIGNIFICANCE: Our results suggest that the EE is involved in the increased cardiac ß1-AR contractility in the early phase of endotoxemic shock. This effect is mediated through the activation of COX1 and COX2 and suggests these may be novel putative therapeutic targets during endotoxemic shock.

Increased beta2-adrenoceptors in doxorubicin-induced cardiomyopathy in rat.

BACKGROUND: The toxicity of doxorubicin, leading to an irreversible heart failure, limits its use as chemotherapeutic agent. The beneficial effects of early administration of ß-blocker were reported in patients with heart failure due to doxorubicin, suggesting an important role of ß-adrenoceptors (ß-ARs). This study aimed to identify a putative target (ß-AR and/or its effectors) at the early phase of a chronic doxorubicin-induced cardiomyopathy (Dox-CM) in a rat model. METHODOLOGY: Dox-CM was induced by six doxorubicin injections (cumulative dose: 15 mg x kg(-1)) and validated by echocardiography and left ventricle (LV) catheterization. The ß-AR protein expressions in LV were evaluated by western-blot at days 35 (d35) and 70 (d70) after the first doxorubicin injection. Ex vivo cardiac contractility (dP/dtmax, dP/dtmin) was evaluated on isolated heart in response to specific ß-AR stimulations at d35. RESULTS: At d35, Dox-CM hearts were characterized by mild LV systolic and diastolic dysfunctions, which were exacerbated at d70. In Dox-CM hearts, ß3-AR expression was only decreased at d70 (-37±8%). At d35, ß1-AR expression was decreased by 68±6%, but ex vivo ß1-AR function was preserved due to, at least in part, an increased adenylyl cyclase response assessed by forskolin. ß2-AR expression was increased both at d35 (+58±22%) and d70 (+174±35%), with an increase of ex vivo ß2-AR response at d35. Inhibition of Gi protein with pertussis toxin did not affect ß2-AR response in Dox-CM hearts, suggesting a decoupling of ß2-AR to Gi protein. CONCLUSION: This study highlights the ß1/ß2-AR imbalance in early Dox-CM and reveals the important role that ß2-AR/Gi coupling could play in this pathology. Our results suggest that ß2-AR could be an interesting target at early stage of Dox-CM.