Abstract 311: Early Losartan Treatment Prevents the Developmental Programming of Cardiac Dysfunction Caused by Neonatal High Oxygen Exposure in Rats

Neonatal oxidative stress is a major postnatal deleterious factor predisposing preterm born infants to classical complications of prematurity (retinopathy, bronchopulmonary dysplasia) which are characterized by impaired vascular development. Our group has previously shown that rats transiently exposed to high O2 as newborns (mimicking human preterms oxidative stress conditions) develop high blood pressure (BP), cardiac remodeling and dysfunction later in life, in part mediated by the renin angiotensin system (RAS). Cardiac RAS activation is characterized by AT1/AT2 receptors imbalance, with increased AT1R at adult age. In order to study the role of RAS at early stages of the developmental programming of cardiac dysfunction caused by high O2 exposure, we assessed whether an early and short-term treatment with AT1R blocker Losartan, prevents cardiac alterations at young male 4 wks-old rats (prior to the elevation of BP in this model). Sprague-Dawley newborns rats were kept with their mother in 80% O2 (O2 group, n=9) or room air (Ctrl, n=9) from days 3-10 of life (P3-P10). Losartan (LOS, n=10, 20 mg/Kg) or water was administered by gavage in O2 rats from P8-P10 (last 2 days of O2 to avoid impact on nephrogenesis). At 4 wks, echocardiography reveals that O2 rats have decreased fraction of shortening compared to Ctrl (FS: 37±2 vs 42±2 %), suggesting impaired systolic function in O2. Cardiac hypertrophy evaluated by heart/body weight and cardiomyocyte surface area (CSA) is also increased in O2 vs Ctrl (141±13 vs 118±4 μm2). LOS treatment prevented the impairment of systolic function in O2 by ameliorating FS (43±2 %) and reducing CSA (121±11 μm2). LOS treatment also modulated RAS genes expression (RT-PCR): LOS restored AT1/AT2 balance in O2 hearts by decreasing AT1b subunit (0.8±0.2 O2 vs 1.3±0.3 O2+LOS vs 0.9±0.2 Ctrl) as well as increasing ACE2 (1.5±0.4 O2 vs 0.8±0.1 O2+LOS vs 1.1±0.4 Ctrl) expressions. In conclusion, a short-term treatment with LOS during neonatal O2 exposure prevents the impairment of cardiac systolic function and hypertrophy at young age. This data reinforces the key role of RAS in the developmental programming of cardiac dysfunction and reveals LOS as an effective strategy to prevent early cardiac alterations caused by neonatal high O2 exposure.