The influence of lactation on postpartum murine heart growth

The cardiovascular system adapts to meet rising physiological demands throughout pregnancy. Notably, the left ventricle grows to support this increased workload, which is thought to reverse after delivery. Yet, whether the heart returns to its pre-pregnant size, shape, and function postpartum is unclear. This postpartum cardiac recovery has been historically studied in rodents. However, despite previous research showing that postpartum-specific conditions like lactation affect hemodynamics and heart weight, the relationship between these hemodynamic changes and cardiac growth remains unclear. In this study, we investigate the impact of lactation on postpartum cardiac recovery. We monitored changes in left ventricular mass, volume, and function throughout pregnancy and postpartum in mice using 4D cardiac ultrasound in animals allowed to nurse their pups for 21 days postpartum and in those whose pups were removed immediately after delivery. We analyzed the relationship between the observed hemodynamics and heart growth in these mice using an existing multiscale computational model of heart growth. Here, we observe that pregnancy-induced cardiac hypertrophy reverses by one week postpartum in non-lactating mice but continues increasing after delivery in lactating mice. Our computational analysis suggests that hemodynamic and biological factors have distinct but complementary roles in driving postpartum growth. Further, our animal-specific simulations indicate that individual hemodynamic changes contribute to the observed variability in experimental heart growth, particularly throughout lactation. Overall, this study provides a detailed timeline of cardiac hypertrophy during and after pregnancy, emphasizes the significance of lactation status on postpartum recovery, and highlights the importance of hemodynamics to this phenomenon.