Early-Life Sodium Depletion Impairs Breathing Patterning During Normoxic Conditions in C57BL/6J mice

Sodium (Na) depletion from unrecognized and unreplenished urine Na losses contributes to suboptimal postnatal growth in preterm infants, which in turn increases the risk of neonatal morbidities. Na depletion is further exacerbated by diuretic treatment, commonly used to treat respiratory disorders such as bronchopulmonary dysplasia. Our previous work in mice shows that early-life Na restriction programs long-term changes in energy balance and sympathetic drive through a brain RAS-dependent mechanism, highlighting the critical role of Na balance in early development for somatic growth and cardiometabolic health. Based upon these relationships, we sought to examine whether early-life Na depletion contributes adversely to lung development and breathing patterning. Three mouse models of Na depletion were used to elucidate the distinct effects of chronic dietary Na depletion versus acute natriuresis upon short and long-term breathing patterning assessed by whole-body plethysmography (WBP) in chambers maintained at 21% O2 for 30-40 minutes. Frequency (bpm), Tidal Volume (VT, mL/breath/100g), Minute Ventilation (VE, mL/min/100g) and Inspiratory Drive (VT/Ti, mL/s) were analyzed by 2-way ANOVA. Significance denoted as *p≤0.05 between diet groups. Sexes were combined for analysis. Data are presented as mean±SEM. Restricting dietary Na supply to the dam (0.04% Na diet; E14.5-P21) while also administering furosemide to the pups daily (P10-P13, 30 mg/kg ip) resulted in increased VT (control n=13: 0.397±0.03 mL/breath/100g vs expt n=13: 0.465±0.03 mL/breath/100g, p<0.03) and VE (65.52±3.9 vs 77.33±5.0 mL/min/100g, p<0.02) between PD21-35. In addition, reduced breathing frequency (control n=14: 169.2±7.9 bpm vs expt n=12: 149.9±3.5 bpm, p<0.03) was observed P63-70. Some of these effects were similarly induced when dams were Na restricted, but furosemide was not administered. When furosemide was administered to pups of dams that were provided normal (0.15% Na) diet, some effects at P63-70 still manifested in male offspring: reduced VE (control n=6: 93.7±5.8 mL/min/100g vs expt n=4: 68.9±10.5 mL/min/100g, p<0.03) and VT/Ti (control n=6: 1.22±0.2 mL/s vs expt n=4: 0.82±0.2 mL/s, p<0.09). Notably, lung morphology was unchanged by any of these three interventions. Together these results lead us to conclude that Na depletion in early life, induced by maternal Na restriction with or without simultaneous diuretic administration to the pup, variably causes changes in ventilatory functions that persist into young adulthood. Further studies are needed to elucidate the mechanisms by which early-life Na depletion disrupts neuronal control of breathing. This study implicates Na homeostasis as a therapeutic target during perinatal development to improve preterm infant respiratory outcomes. The authors gratefully acknowledge Kelsey Wackman, MCW's Biomedical Resource Center, CRI's Histology Core, NIH(DK133121) and Children’s Research Institute (CRI22700). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.