Abstract 360: Early Life Stress Increases Hematocrit and Endothelin-1 in Mice

Abstract

In humans, early life stress (ELS) is an independent risk factor for adult cardiovascular disease (CVD). We have shown that mice subjected to ELS by maternal separation with early weaning (MSEW), develop vascular endothelial dysfunction in adulthood. A marker of endothelial dysfunction and CVD is high hematocrit, an abnormally elevated level of circulating red blood cells. Hematocrit is largely regulated by erythropoietin (EPO), a protein that is released predominantly from the kidney under conditions of hypoxia. We hypothesized that MSEW increases circulating EPO and hematocrit in adult male mice. We used the MSEW model in C57BL6J mice to study the mechanisms of ELS-mediated alteration in hematocrit. MSEW litters were subjected to maternal separation 4h/day (postnatal day (PD) 2-5) and 8h/day (PD6-16), and weaned at PD17. Control (CON) litters were undisturbed until weaning at PD21. At 13 weeks of age, blood was collected from CON and MSEW male mice by cardiac puncture and lung tissue was excised. Hematocrit of MSEW mice was significantly higher than CON mice (46.2 ± 0.03 vs 43.3 ± 0.03%, p = 0.004). Plasma EPO, as measured by ELISA, was elevated in MSEW mice, however not significantly (112.89 ± 51.32 vs 61.62 ± 20.73 pg/ml, p = 0.06). We further hypothesized that MSEW enhances circulating endothelin-1 (ET-1) levels, a vasoactive peptide regulated by hypoxia and EPO. We found that plasma ET-1 was significantly increased in MSEW mice compared to CON (1.55 ± 0.41 vs 1.26 ± 0.23 pg/ml, p = 0.02). Endothelin receptor type A and B density and binding in lung, as measured by radioligand binding, was not different between groups, suggesting that increased circulating ET-1 in MSEW mice was not due to decreased ET-1 clearance in the lungs and most likely is due to increased production of ET-1. Taken together, our data suggest that MSEW-induced endothelial dysfunction may be mediated by an interplay of increased circulating red blood cells and elevated ET-1 production. Further studies are necessary to determine the exact role of these factors in this phenomenon.