Anne-Marie Koop

38 mechanisms against oxidative stress7, and in line with this we found that HO-1 was specifically upregulated in PAB+CF ( figure 4f ). We could not demonstrate differences in NOX-4 activation ormacrophage infiltration between PAB- and PAB+CF ( data not shown ). The amount of RV hypertrophy was equal in PAB- and PAB+CF, whether expressed as (normalized) RV weight or cardiomyocyte cross sectional surface area ( figure 4b,c,e ). Also mRNA expression of genes involved in hypertrophy (myosin heavy chain- isoforms, regulator of calcineurin 1) and the natriuretic peptides type A and B were increased equally in PAB- and PAB+CF ( figure 4f ). However, mRNA expression of the two isoforms of actin was different in PAB- and PAB+CF. The predominant isoform (ACTC) was normal in PAB-, but downregulated in PAB+CF ( figure 4f ). The fetal isoform (ACTA) which is known to be upregulated in response to stresswas indeed upregulated in pressure load, but ~50% less in PAB+CF than in PAB- ( figure 4f ). Insufficient capillary growth to supply the hypertrophic myocardium is suggested to be a main cause of pressure-load induced heart failure7. In both groups capillary density was decreased ( figure 4e ), accompanied by a reduction in VEGF-A and VEGF receptor type 2 expression ( data not shown ). However, in PAB+CF the number of capillaries per cardiomyocyte was significantly less than in PAB- ( figure 4d ). Cardiac index and voluntary exercise predict the onset of RVF with clinical symptoms We performed echocardiography and voluntary exercise measurements at 35 days after PAB surgery, well before the onset of clinical RVF (52±5 days). Retrospectively comparing PAB- and PAB+CF rats, we found that voluntarily run distance, RV stroke volume,TAPSEandcardiacindex(bothwhencardiacoutputwasindexedforbodyweight or tibia length) were all significantly lower at 5 weeks in the rats that later developed clinicalRVFascomparedwiththosethatdidnotdevelopsymptomsofRVF( figure5a-d ). In contrast, there were no differences between PAB+CF and PAB- with regard to ventricular dilatation and tricuspid insufficiency at 5weeks ( table 1 ).While significantly different between PAB+CF and PAB-, cardiac index ( figure 5e ) and TAPSE ( table 1 ) were stable from 5 weeks onward, also in rats that developed clinical RVF. The hemodynamic data of the PAB- group (which was prematurely terminated concurrently with the PAB+CF group) and the PAB rats that survived 11 weeks were similar ( supplemental table 1 ).