Degradation of the endothelial glycocalyx is associated with chylomicron leakage in mouse cremaster muscle microcirculation.

A thick endothelial glycocalyx contributes to the barrier function of vascular endothelium in macro- and microcirculation. We hypothesised in the current study that diet-induced hyperlipidaemia perturbs the glycocalyx, resulting in decreased dimensions of this layer and increased transendothelial lipoprotein leakage in capillaries. Glycocalyx thickness was measured in mouse cremaster muscle capillaries by intravital microscopy from the distance between flowing red blood cells and the endothelial surface. In control C57BL/6 mice on standard chow, glycocalyx thickness measured 0.58 ± 0.01 (mean ± SEM) µm, and no lipoproteins were observed in the tissue. After three months administration of an either mild or severe high-fat / high-cholesterol diet (HFC) to C57BL/6 and ApoE3-Leiden mice, circulating large lipoproteins appeared into the subendothelial space in an increasing proportion of cremaster capillaries, and these capillaries displayed reduced glycocalyx dimensions of 0.40 ± 0.02 and 0.30 ± 0.01 µm (C57BL/6 mice), and 0.37 ± 0.01 and 0.28 ± 0.01 µm (ApoE3-Leiden mice), after the mild and severe HFC diet, respectively. The chylomicron nature of the accumulated lipoproteins was confirmed by observations of subendothelial deposition of DiI-labeled chylomicrons in capillaries after inducing acute glycocalyx degradation by heparitinase in normolipidaemic C57BL/6 mice. It is concluded that while under control conditions the endothelial glycocalyx contributes to the vascular barrier against transvascular lipoprotein leakage in the microcirculation, diet-induced hyperlipidaemia reduces the thickness of the glycocalyx, thereby facilitating leakage of chylomicrons across the capillary wall.

Differential structural adaptation to haemodynamics along single rat cremaster arterioles.

We tested the hypothesis that under physiological conditions, arterioles match their diameter to the level of shear stress. Haemodynamic and anatomical data were obtained in segments of the first-order arteriole of the rat cremaster muscle. Along this segment of ~10 mm in length, local blood pressure decreased from 68 +/- 4 mmHg upstream to 54 +/- 3 mmHg downstream (n = 5). Pulse pressure decreased from 8.2 +/- 1.3 mmHg upstream to 4.1 +/- 0.6 mmHg downstream. At the same locations, an increase in arteriolar diameter was measured in vivo, from 179 +/- 4 microm upstream to 203 +/- 4 microm downstream (n = 10). In vitro pressure-diameter relations of maximally dilated vessels showed that the passive diameter was larger in downstream than upstream segments over a 15-125 mmHg pressure range (n = 18). The wall stress was similar for the upstream vs. downstream location: 266 +/- 16 vs. 260 +/- 14 mN mm-2. However, shear stress decreased from 30 +/- 5 to 21 +/- 5 dyn cm-2 (3.0 +/- 0.5 to 2.1 +/- 0.5 N m-2; n = 4) along the artery. In conclusion, these results demonstrate that shear stress is not the only factor in determining vascular calibre. We suggest that arteriolar calibre may rather depend on an interplay between shear stress and the local pressure profile.