Abstract P3008: Beta Adrenergic Receptor Activation Causes Endothelial Glycocalyx Degradation

The endothelial glycocalyx is a proteoglycan and glycoprotein matrix that coats the luminal surface of endothelial cells. It is an important component of the permeability barrier function of endothelial cells, including in the glomerular capillaries. Furthermore, it is a sensor of shear stress, and in vessels treated with enzymes to remove the glycocalyx do not exhibit flow-mediated vasodilation. Sparse previous studies have implicated a reduced glycocalyx thickness in hypertensive patients, but the causative signaling mechanisms have not been investigated. We and others have found that the endothelial glycocalyx can be studied in cultured endothelial cells if the medium contains significant soluble protein. We hypothesized that elevated catecholamines cause shedding of the endothelial glycocalyx in vitro . We cultured human umbilical vein endothelial cells (HUVECs) in M200 medium supplemented with 1% bovine serum albumin to permit development of a glycocalyx. We exposed these cells to concentrations of epinephrine, norepinephrine, phenylephrine, or isoproterenol from 0.01 to 10 μM for 30 minutes. We then imaged the glycocalyx using fluorescently labelled wheat germ agglutinin. We found that norepinephrine, epinephrine, and isoproterenol all caused a significant decrease in the endothelial glycocalyx staining intensity (5.82 ± 0.28 vs. 4.82 ± 0.21, 6.82 ± 0.28 vs. 5.09 ± 0.25, 7.46 ± 0.33 vs. 6.51 ± 0.28, at 1 μM, 1 μM, and 0.1 μM, respectively). However, phenylephrine caused an increase in glycocalyx staining intensity (6.27 ± 0.25 vs. 7.72 ± 0.32 at 1 μM). These results suggest that catecholamines acutely cause degradation of the glycocalyx in endothelial cells, but only when β adrenergic receptors are involved, since phenylephrine actually acted to increase glycocalyx. Future work will be needed to investigate the pathophysiological role of the reduced glycocalyx in hypertension. Furthermore, in vivo experiments are needed to determine whether these results are applicable to endothelial cells in the complex environment of intact blood vessels. Future work will also investigate the signaling mechanisms leading from adrenergic receptor activation to enzymatic degradation of the glycocalyx.