Heparan sulphate and hyaluronic acid components of the glycocalyx do not play a role in flow-mediated dilation of the iliac in the anaesthetized pig

Procedures to Evaluate the Role of Heparan Sulfate on the Reactivity of Resistance and Conductance Arteries Ex Vivo

Evidence is emerging that disruption of the endothelial glycocalyx might contribute importantly to arterial dysfunction in the context of diabetes. One approach to assess the integrity of the endothelium and the vascular smooth muscle cell layer, in the absence of neural, humoral, and mechanical influences, is by measuring arterial vasomotion ex vivo. Here we describe a procedure to assess non-receptor-mediated vasoconstriction, receptor-mediated vasoconstriction, and endothelium-dependent and -independent vasodilation, in resistance and conductance arteries pressurized to 60 mmHg. In addition to evaluating vasoreactivity using isobaric approaches, the same experimental set-up can be used to initiate a pressure gradient across the artery such that intraluminal, flow-mediated vasodilation can be measured. After recording endothelium-dependent vasodilation using isobaric or flow-mediated approaches, identical interventions can be completed in the presence of enzymes that cleave biologically active heparan sulfates into inactive disaccharide and oligosaccharide fragments to assess the contribution from: (a) endothelial-derived substances (e.g., nitric oxide via nitric oxide synthase inhibition); or (b) important components of the glycocalyx (e.g., removal of heparan sulfate via heparitinase III treatment). Here, we show that acute disruption of a predominant glycosaminoglycan i.e., heparan sulfate impairs intraluminal flow-mediated vasodilation in murine resistance arteries.

The vascular glycocalyx is not a mechanosensor in conduit arteries in the anesthetized pig

Background

The role of the glycocalyx as the endothelial sensor of an increase in blood flow was assessed in the iliac artery in vivo.

Methods

Acetylcholine-induced flow mediated dilation was evaluated before and after vascular glycocalyx disruption. This was accomplished by exposing the iliac lumen to the chemotactic agent fMLP (1 μM; n = 6 pigs), concomitant heparinase III (100 mU ml^-1) and hyaluronidase (14 mg ml^-1) (n = 4), and neuraminidase (140 mU ml^-1; n = 5), for 20 min in separate iliac artery preparations. Only one lumen intervention per iliac was conducted.

Results

For the heparinase III + hyaluronidase experiment, the iliac diameter increased by an average of 0.54 ± 0.11 mm before and 0.45 ± 0.03 mm after the enzymes (P = 0.42; paired Student's t test). The iliac diameter increased by 0.31 ± 0.02 mm before and 0.29 ± 0.07 mm after fMLP exposure (P = 0.7) and the diameter increased by 0.54 ± 0.11 mm before and 0.54 ± 0.09 mm after neuraminidase exposure (P = 0.98). In all cases, the shear stress changes before and after lumen exposure were not significantly different to each other.

Conclusion

There was no significant reduction in flow mediated dilation of the iliac in response to any of the interventions conducted. Therefore, the vascular endothelial glycocalyx as whole is not required for flow mediated dilation in conduit arteries in the intact animal.