Background Hemodynamic load regulates myocardial function and gene expression. We tested the hypothesis that afterload and preload despite similar average load result in different phenotypes. Methods and Results Afterload and preload were compared in mice with transversal aortic constriction (TAC) and aorto-caval shunt (Shunt). When compared to sham mice, six hours after surgery, systolic wall stress (afterload) was increased in TAC (+40%, P<0.05), diastolic wall stress (preload) was increased in Shunt (+277%, P<0.05) and TAC (+74%, P<0.05) and mean total wall stress was similarly increased in TAC (69%) and Shunt (67%) (TAC vs. Shunt: not significant (n.s.), each P<0.05 vs. Sham). At 1 week, left ventricular weight/tibia length was significantly increased by 22% in TAC and 29% in Shunt (n.s. TAC vs. Shunt). After 24 hours and 1 week, calcium/calmodulin dependent protein kinase II (CaMKII) signaling was increased in TAC. This resulted in altered calcium cycling, including increased L-type calcium current, calcium transients, fractional SR release and calcium spark frequency. In Shunt, Akt phosphorylation was increased. TAC was associated with inflammation, fibrosis and cardiomyocyte apoptosis. The latter was significantly reduced in CaMKIIδ-KO TAC mice. 157 mRNAs and 13 microRNAs were differentially regulated in TAC vs. Shunt. After 8 weeks, fractional shortening was lower and mortality higher in TAC Conclusions Afterload results in maladaptive fibrotic hypertrophy with CaMKII-dependent altered calcium cycling and apoptosis. Preload is associated with Akt activation without fibrosis, little apoptosis, better function and lower mortality. This indicates that different loads result in distinct phenotype differences which may require specific pharmacological interventions.

Aims Pressure overload (PO) and volume overload (VO) lead to concentric or eccentric hypertrophy. Previously, we could show that activation of signalling cascades differ in in vivo mouse models. Activation of these signal cascades could either be induced by intrinsic load sensing or neuro‐endocrine substances like catecholamines or the renin‐angiotensin‐aldosterone system. Methods and results We therefore analysed the activation of classical cardiac signal pathways [mitogen‐activated protein kinases (MAPKs) (ERK, p38, and JNK) and Akt‐GSK3β] in in vitro of mechanical overload (ejecting heart model, rabbit and human isolated muscle strips). Selective elevation of preload in vitro increased AKT and GSK3β phosphorylation after 15 min in isolated rabbit muscles strips (AKT 49%, GSK3β 26%, P < 0.05) and in mouse ejecting hearts (AKT 51%, GSK49%, P < 0.05), whereas phosphorylation of MAPKs was not influenced by increased preload. Selective elevation of afterload revealed an increase in ERK phosphorylation in the ejecting heart (43%, P < 0.05), but not in AKT, GSK3β, and the other MAPKs. Elevation of preload and afterload in the ejecting heart induced a significant phosphorylation of ERK (95%, P < 0.001) and showed a moderate increased AKT (P = 0.14) and GSK3β (P = 0.21) phosphorylation, which did not reach significance. Preload and afterload elevation in muscles strips from human failing hearts showed neither AKT nor ERK phosphorylation changes. Conclusions Our data show that preload activates the AKT–GSK3β and afterload the ERK pathway in vitro, indicating an intrinsic mechanism independent of endocrine signalling.

Darstellung des Proteins p38 mittels Western-Immunoblot-Methode 24 Stunden und 7 Tage nach Intervention.

We would like to thank Reil et al for their interesting discussion. They argue that wall stress of mice with transversal aortic constriction (TAC) may have been higher than those of mice with aortocaval shunt (shunt), which would be supported by lack of brain natriuretic peptide expression in shunt. We believe that we can disprove the arguments and the conclusion of Reil et al for the following reasons:1. After 1 week of increased load under both conditions, hypertrophy, as measured by left ventricular weight per tibia length, is similarly increased in both models, and this holds true for myocyte minimal fiber diameter as well (Figure 1 of our The argument that the pericardium would reduce preload is interesting. However, to our knowledge, pericardial forces are largely unknown in mice. Unlike in human or large animal models, the mouse pericardium is thin. Therefore, the contribution to left ventricular end-diastolic pressure generation should be rather low. In addition, volume overload occurs in all heart chambers in our shunt model. Therefore, calculation of the transmural gradient (left ventricular end-diastolic pressure minus right atrial pressure) would lead to a low gradient, and the left ventricular pressure might be underestimated. Finally, the argument that the isovolumetric decay of left ventricular diastolic pressure was not included in the wall stress calculation is well taken. Accordingly, to estimate the impact of inclusion of isovolumetric decay, we recalculated diastolic and total wall stress. The diastole was divided in the part of the isovolumetric decay and in the residual part, and total wall stress was newly calculated. Mean total wall stress was then 9.68Ϯ0.22 mm Hg in sham, 15.17Ϯ1.17 mm Hg in shunt (PϽ0.05 versus sham), and 15.43Ϯ0.66 mm Hg in TAC (PϽ0.01 versus sham). Mean total wall stress was increased in shunt by 57% and in TAC by 59% (Pϭ0.86 shunt versus TAC). Therefore, inclusion of the isovolumetric decay in the calculation of diastolic wall stress does not lead to a significantly higher wall stress in TAC compared with shunt.In conclusion, afterload leads to maladaptive hypertrophy, whereas preload has a more favorable phenotype. This results from distinct differences in hypertrophic signal activation with both forms of load despite comparable increases in stress-time integral. DisclosuresNone. Circulation. 1992;86:513-521. 5. Segers P, Morimont P, Kolh P, Stergiopulos N, Westerhof N, Verdonck P. Arterial elastance and heart-arterial coupling in aortic regurgitation are determined by aortic leak severity. Karl