Involvement of Vasopressin in Tissue Hypoperfusion during Cardiogenic Shock Complicating Acute Myocardial Infarction in Rats.

Acute heart failure (AHF) due to acute myocardial infarction (AMI) is likely to involve cardiogenic shock (CS), with neuro-hormonal activation. A relationship between AHF, CS and vasopressin response is suspected. This study aimed to investigate the implication of vasopressin on hemodynamic parameters and tissue perfusion at the early phase of CS complicating AMI. Experiments were performed on male Wistar rats submitted or not to left coronary artery ligation (AMI and Sham). Six groups were studied Sham and AMI treated or not with either a vasopressin antagonist SR-49059 (Sham-SR, AMI-SR) or agonist terlipressin (Sham-TLP, AMI-TLP). Animals were sacrificed one day after surgery (D1) and after hemodynamic parameters determination. Vascular responses to vasopressin were evaluated, ex vivo, on aorta. AHF was defined by a left ventricular ejection fraction below 40%. CS was defined by AHF plus tissue hypoperfusion evidenced by elevated serum lactate level or low mesenteric oxygen saturation (SmO2) at D1. Mortality rates were 40% in AMI, 0% in AMI-SR and 33% in AMI-TLP. Immediately after surgery, a sharp decrease in SmO2 was observed in all groups. At D1, SmO2 recovered in Sham and in SR-treated animals while it remained low in AMI and further decreased in TLP-treated groups. The incidence of CS among AHF animals was 72% in AMI or AMI-TLP while it was reduced to 25% in AMI-SR. Plasma copeptin level was increased by AMI. Maximal contractile response to vasopressin was decreased in AMI (32%) as in TLP- and SR- treated groups regardless of ligation. Increased vasopressin secretion occurring in the early phase of AMI may be responsible of mesenteric hypoperfusion resulting in tissue hypoxia. Treatment with a vasopressin antagonist enhanced mesenteric perfusion and improve survival. This could be an interesting therapeutic strategy to prevent progression to cardiogenic shock.

Pulmonary hypertension after pneumonectomy: a preclinical model in rats and human pulmonary endothelial cells.

OBJECTIVES: Pulmonary hypertension and heart disease contribute to the high morbidity rate following pneumonectomy (PN). The pathophysiology is still poorly understood. The objective was to investigate the consequences of PN on cardiopulmonary function in rats and to explore in vitro the involved mechanisms. METHODS: Sixty Sprague-Dawley male rats randomly underwent either a right PN (PN group) or sham surgery. Ten rats per group were sacrificed on postoperative days 3, 7 and 28. Cardiopulmonary alterations were investigated by echocardiographic, haemodynamic and histological analyses. In vitro, the shear stress was reproduced using a Flexcell Tension™ cyclic stretch on cultured human pulmonary endothelial cells (P-ECs) to investigate the impact on pulmonary artery smooth muscle cell (PA-SMC) growth. Data are expressed as mean ± SD. RESULTS: Mean pulmonary arterial pressure gradually increased in the PN group to reach 35 ± 7 mmHg on postoperative day 28 vs 18 ± 4 in sham (P = 0.001), likewise the proportion of muscularized distal pulmonary arteries, 83 ± 1% vs 5 ± 1%, respectively (P < 0.001), related to in situ PA-SMC proliferation. The right ventricle area and lateral wall thickness were doubled in the PN group on postoperative day 28. The left ventricle ejection fraction decreased on postoperative days 7 and 28 while the right ventricle function was maintained. In vitro, the human PA-SMC growth was significantly greater when seeded with stretched vs non-stretched P-EC media, highlighting the role of shear stress on the P-EC paracrine function. CONCLUSIONS: Right PN led to pulmonary hypertension and proportional right heart remodelling in rats. The shear stress related to high blood flow alters the pulmonary endothelial paracrine control of SMC growth.

New role of TRPM4 channel in the cardiac excitation-contraction coupling in response to physiological and pathological hypertrophy in mouse.

The transient receptor potential Melastatin 4 (TRPM4) channel is a calcium-activated non-selective cation channel expressed widely. In the heart, using a knock-out mouse model, the TRPM4 channel has been shown to be involved in multiple processes, including ß-adrenergic regulation, cardiac conduction, action potential duration and hypertrophic adaptations. This channel was recently shown to be involved in stress-induced cardiac arrhythmias in a mouse model overexpressing TRPM4 in ventricular cardiomyocytes. However, the link between TRPM4 channel expression in ventricular cardiomyocytes, the hypertrophic response to stress and/or cellular arrhythmias has yet to be elucidated. In this present study, we induced pathological hypertrophy in response to myocardial infarction using a mouse model of Trpm4 gene invalidation, and demonstrate that TRPM4 is essential for survival. We also demonstrate that the TRPM4 is required to activate both the Akt and Calcineurin pathways. Finally, using two hypertrophy models, either a physiological response to endurance training or a pathological response to myocardial infarction, we show that TRPM4 plays a role in regulating transient calcium amplitudes and leads to the development of cellular arrhythmias potentially in cooperation with the Sodium-calcium exchange (NCX). Here, we report two functions of the TRPM4 channel: first its role in adaptive hypertrophy, and second its association with NCX could mediate transient calcium amplitudes which trigger cellular arrhythmias.

Prolonged elevated levels of c-kit+ progenitor cells after a myocardial infarction by beta 2 adrenergic receptor priming.

Endogenous progenitor cells may participate in cardiac repair after a myocardial infarction (MI). The beta 2 adrenergic receptor (ß2-AR) pathway induces proliferation of c-kit+ cardiac progenitor cells (CPC) in vitro. We investigated if ß2-AR pharmacological stimulation could ameliorate endogenous CPC-mediated regeneration after a MI. C-kit+ CPC ß1-AR and ß2-AR expression was evaluated in vivo and in vitro. A significant increase in the percentage of CPCs expressing ß1-AR and ß2-AR was measured 7 days post-MI. Accordingly, 24 hrs of low serum and hypoxia in vitro significantly increased CPC ß2-AR expression. Cell viability and differentiation assays validated a functional role of CPC ß2-AR. The effect of pharmacological activation of ß2-AR was studied in C57 mice using fenoterol administered in the drinking water 1 week before MI or sham surgery or at the time of the surgery. MI induced a significant increase in the percentage of c-kit+ progenitor cells at 7 days, whereas pretreatment with fenoterol prolonged this response resulting in a significant elevated number of CPC up to 21 days post-MI. This increased number of CPC correlated with a decrease in infarct size. The immunofluorescence analysis of the heart tissue for proliferation, apoptosis, macrophage infiltration, cardiomyocytes surface area, and vessel density showed significant changes on the basis of surgery but no benefit due to fenoterol treatment. Cardiac function was not ameliorated by fenoterol administration when evaluated by echocardiography. Our results suggest that ß2-AR stimulation may improve the cardiac repair process by supporting an endogenous progenitor cell response but is not sufficient to improve the cardiac function.

Ryanodine receptor leak mediated by caspase-8 activation leads to left ventricular injury after myocardial ischemia-reperfusion.

Myocardial ischemic disease is the major cause of death worldwide. After myocardial infarction, reperfusion of infracted heart has been an important objective of strategies to improve outcomes. However, cardiac ischemia/reperfusion (I/R) is characterized by inflammation, arrhythmias, cardiomyocyte damage, and, at the cellular level, disturbance in Ca(2+) and redox homeostasis. In this study, we sought to determine how acute inflammatory response contributes to reperfusion injury and Ca(2+) homeostasis disturbance after acute ischemia. Using a rat model of I/R, we show that circulating levels of TNF-α and cardiac caspase-8 activity were increased within 6 h of reperfusion, leading to myocardial nitric oxide and mitochondrial ROS production. At 1 and 15 d after reperfusion, caspase-8 activation resulted in S-nitrosylation of the RyR2 and depletion of calstabin2 from the RyR2 complex, resulting in diastolic sarcoplasmic reticulum (SR) Ca(2+) leak. Pharmacological inhibition of caspase-8 before reperfusion with Q-LETD-OPh or prevention of calstabin2 depletion from the RyR2 complex with the Ca(2+) channel stabilizer S107 ("rycal") inhibited the SR Ca(2+) leak, reduced ventricular arrhythmias, infarct size, and left ventricular remodeling after 15 d of reperfusion. TNF-α-induced caspase-8 activation leads to leaky RyR2 channels that contribute to myocardial remodeling after I/R. Thus, early prevention of SR Ca(2+) leak trough normalization of RyR2 function is cardioprotective.

ATP/UTP activate cation-permeable channels with TRPC3/7 properties in rat cardiomyocytes.

Extracellular purines and pyrimidines have major effects on cardiac rhythm and contraction. ATP/UTP are released during various physiopathological conditions, such as ischemia, and despite degradation by ectonucleotidases, their interstitial concentrations can markedly increase, a fact that is clearly associated with arrhythmia. In the present whole cell patch-clamp analysis on ventricular cardiomyocytes isolated from various mammalian species, ATP and UTP elicited a sustained, nonselective cationic current, I(ATP). UDP was ineffective, whereas 2'(3')-O-(4-benzoylbenzoyl)-ATP was active, suggesting that P2Y(2) receptors are involved. I(ATP) resulted from the binding of ATP(4-) to P2Y(2) purinoceptors. I(ATP) was maintained after ATP removal in the presence of guanosine 5'-[gamma-thio]triphosphate and was inhibited by U-73122, a PLC inhibitor. Single-channel openings are rather infrequent under basal conditions. ATP markedly increased opening probability, an effect prevented by U-73122. Two main conductance levels of 14 and 23 pS were easily distinguished. Similarly, in fura-2-loaded cardiomyocytes, Mn(2+) quenching and Ba(2+) influx were significant only in the presence of ATP or UTP. Adult rat ventricular cardiomyocytes expressed transient receptor potential channel TRPC1, -3, -4, and -7 mRNA and the TRPC3 and TRPC7 proteins that coimmunoprecipitated. Finally, the anti-TRPC3 antibody added to the patch pipette solution inhibited I(ATP). In conclusion, activation of P2Y(2) receptors, via a G protein and stimulation of PLCbeta, induces the opening of heteromeric TRPC3/7 channels, leading to a sustained, nonspecific cationic current. Such a depolarizing current could induce cell automaticity and trigger the arrhythmic events during an early infarct when ATP/UTP release occurs. These results emphasize a new, potentially deleterious role of TRPC channel activation.