cardiac-response-to-adrenergic-stimulation-determined-pressure-volume

Cardiac Response to &#946;-Adrenergic Stimulation Determined by Pressure-Volume Loop Analysis

Determination of the cardiac function is a robust endpoint analysis in animal models of cardiovascular diseases in order to characterize effects of ...

Ruprecht-Karls-Universität Heidelberg

DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim

University Hospital RWTH Aachen

 Cardiac pressure-volume (PV loop) analysis under β-adrenergic stimulation is a powerful method to simultaneously determine intrinsic cardiac function and β-adrenergic reserve in mouse models. Despite its wide use, several key approaches of this method, which can affect murine cardiac function tremendously, have not been experimentally investigated until now. In this study, we investigate the impact of three lines of action during the complex procedure of PV loop analysis: (i) the ventilation with positive end-expiratory pressure, (ii) the time point of injecting hypertonic saline to estimate parallel-conductance, and (iii) the implications of end-systolic pressure-spikes that may arise under β-adrenergic stimulation.  We performed pressure-volume analysis during β-adrenergic stimulation in an open-chest protocol under Isoflurane/Buprenorphine anesthesia. Our analysis showed that (i) ventilation with 2 cmHO positive end-expiratory pressure prevented exacerbation of peak inspiratory pressures subsequently protecting mice from macroscopic pulmonary bleedings. (ii) Estimations of parallel-conductance by injecting hypertonic saline prior to pressure-volume recordings induced dilated chamber dimensions as depicted by elevation of end-systolic volume (+113%), end-diastolic volume (+40%), and end-diastolic pressure (+46%). Further, using this experimental approach, the preload-independent contractility (PRSW) was significantly impaired under basal conditions (-17%) and under catecholaminergic stimulation (-14% at 8.25 ng/min Isoprenaline), the β-adrenergic reserve was alleviated, and the incidence of ectopic beats was increased >5-fold. (iii) End-systolic pressure-spikes were observed in 26% of pressure-volume recordings under stimulation with 2.475 and 8.25 ng/min Isoprenaline, which affected the analysis of maximum pressure (+11.5%), end-diastolic volume (-8%), stroke volume (-10%), and cardiac output (-11%).  Our results (i) demonstrate the advantages of positive end-expiratory pressure ventilation in open-chest instrumented mice, (ii) underline the perils of injecting hypertonic saline prior to pressure-volume recordings to calibrate for parallel-conductance and (iii) emphasize the necessity to be aware of the consequences of end-systolic pressure-spikes during β-adrenergic stimulation.

Assessment of PEEP-Ventilation and the Time Point of Parallel-Conductance Determination for Pressure-Volume Analysis Under β-Adrenergic Stimulation in Mice.

Pathological cardiac remodeling correlates with chronic neurohumoral stimulation and abnormal Ca signaling in cardiomyocytes. Store-operated calcium entry (SOCE) has been described in adult and neonatal murine cardiomyocytes, and Orai1 proteins act as crucial ion-conducting constituents of this calcium entry pathway that can be engaged not only by passive Ca store depletion but also by neurohumoral stimuli such as angiotensin-II. In this study, we, therefore, analyzed the consequences of Orai1 deletion for cardiomyocyte hypertrophy in neonatal and adult cardiomyocytes as well as for other features of pathological cardiac remodeling including cardiac contractile function in vivo. Cellular hypertrophy induced by angiotensin-II in embryonic cardiomyocytes from Orai1-deficient mice was blunted in comparison to cells from litter-matched control mice. Due to lethality of mice with ubiquitous Orai1 deficiency and to selectively analyze the role of Orai1 in adult cardiomyocytes, we generated a cardiomyocyte-specific and temporally inducible Orai1 knockout mouse line (Orai1). Analysis of cardiac contractility by pressure-volume loops under basal conditions and of cardiac histology did not reveal differences between Orai1 mice and controls. Moreover, deletion of Orai1 in cardiomyocytes in adult mice did not protect them from angiotensin-II-induced cardiac remodeling, but cardiomyocyte cross-sectional area and cardiac fibrosis were enhanced. These alterations in the absence of Orai1 go along with blunted angiotensin-II-induced upregulation of the expression of Myoz2 and a lack of rise in angiotensin-II-induced STIM1 and Orai3 expression. In contrast to embryonic cardiomyocytes, where Orai1 contributes to the development of cellular hypertrophy, the results obtained from deletion of Orai1 in the adult myocardium reveal a protective function of Orai1 against the development of angiotensin-II-induced cardiac remodeling, possibly involving signaling via Orai3/STIM1-calcineurin-NFAT related pathways.

Sebastian Segin

Pharmakologisches Institut

Ruprecht-Karls-Universität Heidelberg

Cardiac Response to β-Adrenergic Stimulation Determined by Pressure-Volume Loop Analysis

Sebastian Segin

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Pharmakologisches Institut

Ruprecht-Karls-Universität Heidelberg

Cardiac Response to β-Adrenergic Stimulation Determined by Pressure-Volume Loop Analysis

Pharmakologisches Institut