Immature Endothelial Cells Initiate Endothelin‐Mediated Constriction of Newborn Arteries

The early postnatal period is associated with remarkable changes in the morphology and function of endothelial cells. Newborn arterial endothelial cells have a highly unusual phenotype, which includes minimal NO activity, heightened Rho/ROCK signaling, prominent actin stress fibers and poorly developed cellular junctions. During the immediate postnatal period, arterial endothelial cells then acquire characteristics normally associated with mature protective cells including exuberant NO‐mediated dilation, complex endothelial cellular junctions and reorganization of stress fibers to a cortical actin network. Indeed, the atypical phenotype of immature newborn endothelial cells resembles dysfunctional endothelial cells that contribute to the development of vascular disease. The present experiments were performed to determine whether newborn endothelial cells might express and release endothelin‐1 (ET‐1) and initiate endothelium‐dependent constriction, hallmark features of pathological endothelial dysfunction. Carotid arteries were isolated from newborn (postnatal day 1, P1), P7 and P21 mice and mounted in pressure myographs at a constant transmural pressure of 20 mmHg (mean blood pressure for a P1 mouse). Exogenous ET‐1 caused similar concentration‐dependent constrictions of P1, P7 and P21 arteries. Endothelial stimulation with A23187 or thrombin caused powerful constriction in P1 arteries, no significant change in arterial diameter in P7 arteries, and powerful dilatation in P21 arteries. In P1 arteries, constriction to thrombin or A23187 was inhibited by endothelial denudation, by ET‐1 receptor antagonists (BQ123 or BQ123 plus BQ788), or by inhibition of endothelin converting enzyme (ECE) (phosphoramidon or SM19712). ET‐1 receptor antagonism did not significantly affect responses to thrombin or A23187 in more mature P7 and P21 arteries. Endothelial expression of ET‐1 peptides, assessed by immunofluorescent analysis, was significantly increased in P1 compared to P21 arteries. Endothelial stimulation with thrombin rapidly increased the endothelium‐dependent release of ET‐1 from P1 but not P21 arteries. Therefore, newborn endothelial cells express high levels of ET‐1 peptides, rapidly release ET‐1 in response to endothelial stimulation and initiate ET‐1 mediated endothelium‐dependent constriction. This activity is lost as the endothelium matures in the immediate postnatal period. The unusual phenotype of newborn endothelium including heightened activity of ET‐1 is reminiscent of pathological endothelial dysfunction, which may reflect reemergence of the newborn phenotype. Support or Funding Information NIH R01 HD078639