1 2 Prenatal hypoxia programs changes in β - adrenergic signaling and postnatal 3 cardiac contractile dysfunction 4 5

22 Prenatal hypoxia leads to an increased risk of adult cardiovascular disease. We have previously 23 demonstrated a programming effect of prenatal hypoxia on the cardiac beta-adrenergic (βAR) response. 24 The aim of this study was to determine 1) if the decrease in βAR sensitivity in prenatally hypoxic 5 week 25 chicken hearts is linked to changes in β1AR/β2ARs, Gαi expression and cAMP accumulation and 2) if 26 prenatal hypoxia has an effect on heart function in vivo. 27 We incubated eggs in normoxia (N, 21% O2) or hypoxia from day 0 (H, 14% O2) and raised the 28 post-hatchlings to 5 weeks of age. Cardiac β1AR/β2ARs were assessed through competitive binding of 29 [H]CGP-12177 with specific β1AR or β2AR blockers. Gαs and Gαi proteins were assessed by Western blot 30 and cAMP accumulation by ELISA. Echocardiograms were recorded in anesthetized birds to evaluate 31 diastolic/systolic diameter and heart rate and tissue sections were stained for collagen. 32 We found an increase in relative heart mass, β1ARs and Gαs in prenatally hypoxic hearts. cAMP 33 levels after isoproterenol stimulation and collagen content was not changed in H compared to N but in 34 vivo echocardiograms showed systolic contractile dysfunction. 35 The changes in βAR and G-protein subtypes may be indicative of an early compensatory stage in 36 the progression of cardiac dysfunction, further supported by the cardiac hypertrophy and systolic 37 contractile dysfunction. We suggest that it is not the changes in the proximal part of the βAR system that 38 causes the decreased cardiac contractility, but Ca handling mechanisms further downstream in the βAR 39 signaling cascade. 40 41