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      In vitro Study of Starling’s Hypothesis in a Cultured Monolayer of Bovine Aortic Endothelial Cells


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          Starling’s hypothesis that fluid movement across the microvascular wall is determined by the transmural differences in hydrostatic and osmotic pressures was tested using an in vitro model comprised of bovine aortic endothelial cells grown on a porous support. In all experiments, a 1% bovine serum albumin (BSA) solution was maintained in the abluminal reservoir and the luminal reservoir contained either a 1 or a 5.5% BSA solution. The global osmotic pressure difference across the endothelial layers was thus either 0 or 20.3 cm H<sub>2</sub>O. When the luminal concentration of BSA was changed from 1 to 5.5% at a hydrostatic pressure differential of 5, 10 or 20 cm H<sub>2</sub>O, no reverse flow (in the reabsorption direction) was observed even though the hydrostatic pressure differential was far below the global osmotic pressure differential. In another case, the hydrostatic pressure differential was dropped quickly from 20 to 5 cm H<sub>2</sub>O, while a constant osmotic pressure differential was maintained by 5.5% BSA in the luminal reservoir. A strong transient reabsorption flow was observed over a 30-second period which diminished to undetectable levels within 2.5 min; then a sustained steady-state filtration flow was observed after 20 min. These in vitro experiments support other studies in capillaries showing transient reabsorption that decays to steady-state filtration at longer times.

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          Most cited references 6

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          A new view of Starling's hypothesis at the microstructural level.

           S Weinbaum,  X. Hu (1999)
          In this paper we quantitatively investigate the hypothesis proposed by Michel (Exp. Physiol. 82, 1-30, 1997) and Weinbaum (Ann. Biomed. Eng. 26, 1-17, 1998) that the Starling forces are determined by the local difference in the hydrostatic and colloid osmotic pressure across the endothelial surface glycocalyx, which we propose is the primary molecular sieve for plasma proteins, rather than the global difference in the hydrostatic and oncotic pressure across the capillary wall between the plasma and tissue, as has been universally assumed until now. A spatially heterogeneous microstructural model is developed to explain at the cellular level why there is oncotic absorption at low capillary pressures in the short-lived transient experiments of Michel and Phillips (J. Physiol. 388, 421-435, 1987) on frog mesentery capillary, but a small positive filtration once a steady state is achieved. The new model also predicts that the local protein concentration behind the surface glycocalyx can differ greatly from the tissue protein concentration, since the convective flux of proteins through the orifice-like pores in the junction strand will greatly impede the back diffusion of the proteins into the lumen side of the cleft when the local Peclet number at the orifice is >1. The net result is that the filtration in the capillaries is far less than heretofore realized and there may be no need for venous reabsorption. Copyright 1999 Academic Press.
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            Effect of vascular endothelial growth factor on cultured endothelial cell monolayer transport properties.

            Vascular endothelial growth factor (VEGF) is a potent enhancer of microvascular permeability in vivo. To date, its effects on hydraulic conductivity (L(p)) and diffusive albumin permeability (P(e)) of endothelial monolayers have not been thoroughly assessed in vitro. We hypothesized that VEGF affects endothelial transport properties differently depending on vessel location and endothelial phenotype. Using three well-established endothelial cell culture models-human umbilical vein endothelial cells (HUVECs), bovine aortic endothelial cells (BAECs), and bovine retinal microvascular cells (BRECs)-grown on porous, polycarbonate filters we were able to produce baseline transport properties characteristic of restrictive barriers. Our results show 3.1-fold and 5.7-fold increases in endothelial L(p) for BAEC and BREC monolayers, respectively, at the end of 3 h of VEGF (100 ng/ml) exposure. HUVECs, however, showed no significant alteration in L(p) after 3 h (100 ng/ml) or 24 h (25 ng/ml) of incubation with VEGF even though they were responsive to the inflammatory mediators, thrombin (1 U/ml; 27-fold increase in L(p) in 25 min) and bradykinin (10 microM; 4-fold increase in L(p) in 20 min). Protein kinase C (PKC) and nitric oxide (NO) are downstream effectors of VEGF signaling. BAEC L(p) was responsive to activation of NO (SNAP) and PKC (PMA), whereas these agents had no effect in altering HUVEC L(p). Moreover, BAECs exposed to the PKC inhibitor, staurosporine (50 ng/ml), exhibited significant attenuation of VEGF-induced increase in L(p), but inhibition of nitric oxide synthase (NOS) with L-NMMA (100 microM) had no effect in altering the VEGF-induced increase in L(p). These data provide strong evidence that in BAECs, the VEGF-induced increase in L(p) is mediated by a PKC-dependent mechanism. Regarding diffusive albumin P(e), at the end of 3 h, BAECs and BRECs showed 6.0-fold and 9. 9-fold increases in P(e) in response to VEGF (100 ng/ml), whereas VEGF had no significant effect after 3 h (100 ng/ml) or 24 h (25 ng/ml) in changing HUVEC P(e). In summary, these data indicate that VEGF affects endothelial transport properties differently depending on the vessel type and that differences in cell signaling pathways underlie the differences in VEGF responsiveness. Copyright 2000 Academic Press.
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              1997 Whitaker Distinguished Lecture: Models to Solve Mysteries in Biomechanics at the Cellular Level; A New View of Fiber Matrix Layers


                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                August 2003
                26 September 2003
                : 40
                : 4
                : 351-358
                Biomolecular Transport Dynamics Laboratory, Departments of Chemical Engineering and Bioengineering, The Pennsylvania State University, University Park, Pa., USA
                72699 J Vasc Res 2003;40:351–358
                © 2003 S. Karger AG, Basel

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                Page count
                Figures: 5, Tables: 1, References: 21, Pages: 8
                Research Paper


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