The effect of luminal flow in rabbit carotid artery on transmural fluid transport

Abstract

SUMMARYThe steady-state flow of fluid across the wall of the isolated rabbit common carotid artery has been measured in the presence and absence of flow within the lumen of the vessel. The perfusate solution contained either 10 or 40 mg ml-' albumin and transmural flux was measured by monitoring the rate of movement of fluid into a chamber enclosing the artery. Vasomotion was minimized by the inclusion of the vasodilator sodium nitrite in both the perfusate and the outer bathing solution. A relatively slow luminal flow caused a reversible increase in the transmural flux by 20 30 % relative to the value in the absence of flow. The mechanism responsible for the increasc is not clear, but since it was not affccted by the H1 antagonist, mepyramine, it would not appear to have been mediated by histamine release.

A transmural pressure gradient induces mechanical and biological adaptive responses in endothelial cells

“…Traditionally, endothelial transport properties (L p , P d , and ) have been regarded as passive (constant) properties of the endothelium; however, it is now becoming clear that endothelial permeability coefficients depend on hemodynamic forces. Several investigators have shown that endothelial L p increases in response to an increase in fluid wall shear stress using in vitro (11,15,19,40) and in vivo (29,33,49,50) models. In the present study, a step change in the hydrostatic pressure gradient from 0 to 10 cmH 2 O induced a prominent sealing effect in BAEC monolayers (Fig.…”

“…In the present study, J v/A (water flow) and Lp are often used interchangeably because ⌬P is constant; thus changes in J v/A also reflect changes in Lp. There may have been a slight excess of protein near the luminal surface because of concentration polarization driven by volume flux, but this was estimated to have a negligible oncotic effect using a 1% BSA solution (29). Integration of the bubble tracker with a fluorescent detection system allowed simultaneous flux measurements of water and fluorescent-conjugated solutes.…”

“…Gradients of hydrostatic pressure and oncotic pressure across the wall drive fluid transport between the vessel lumen and the underlying tissue. Other investigators have observed that imposing a step increase in the transmural pressure gradient across cells in culture (6,40,44,46) and intact arteries (29,45) leads to an initial elevation, followed by a transient reduction in endothelial transport coefficients. This phenomenon, termed the "sealing effect" (44), appears to be an adaptive mechanism to protect against tissue edema in the face of elevated blood pressure.…”

“…The flow of blood generates a tangential frictional stress (i.e., wall shear stress) that directly acts on the luminal surface of endothelial cells. Several in vitro studies (11,23,28,32,40) and in vivo studies (29,49,50) have shown that shear stress alters transport coefficients in micro-and macrovessel model systems. Blood pressure, on the other hand, is a normal stress that is balanced by the circumferential stress of the vessel wall.…”

Regulation of capillary hydraulic conductivity in response to an acute change in shear

“…Several studies have shown that transvascular exchange can be affected by a change in perfusion rate (14,17,19,32,33,43). A small-pore model has been proposed as a possible mechanism to account for flow-dependent transport of small solutes in cannulated vessels (32); moreover, there have been several recent studies of shearinduced increases in fluid filtration performed in vitro (3, 6, 37) and in vivo (27,40,41). The mechanism by which shear forces could increase L p appear to be dependent on nitric oxide (NO) (3,15,24).…”