Platelets Do Not Alter Flow-Mediated Dilation or Arterial Conduction in vivo

The aim of this study was to investigate whether platelets contribute to shear stress and vascular conductance in the iliac vascular bed in vivo. Flow-mediated dilation of pig iliac was induced by downstream injection of acetylcholine (50 μg), and separately, conductance (ΔF/ΔP) was calculated. This was carried out before and after removal of 1 L of arterial blood in 240 mL increments, and each 240 mL was spun in a centrifuge (1,500 rcf for 7 min); platelet-rich plasma was replaced with equal volume of heparinised saline and reinjected. The circulating platelet count fell from 369 × 10⁹/L (n = 5) to 165 × 10⁹/L (p = 0.01; n = 4; Student's unpaired t). An increase in flow led to an increase in the iliac diameter by 0.49 ± 0.03 mm (mean ± SEM) before platelet reduction and 0.55 ± 0.05 mm after (p = 0.36, Student's paired t, n = 5); the change in arterial conductance was also not significantly affected by platelet reduction, control: 1.44 ± 0.34 mL/min/mm Hg, after platelet reduction: 1.39 ± 0.04 mm (p = 0.55, Student's paired t, n = 4). Therefore, platelets do not contribute to shear stress or conductance in vivo.