Whole-body heat stress and exercise stimulate the appearance of platelet microvesicles in plasma with limited influence of vascular shear stress

Abstract

Intense, large muscle mass exercise increases circulating microvesicles but our understanding of microvesicle dynamics and mechanisms inducing their release remain limited. However, increased vascular shear stress may be involved. Here we manipulated exercise-independent and -dependent shear stress using systemic heat stress with localised single-leg cooling (low shear) followed by single-leg knee extensor exercise with the cooled or heated leg (Study 1, n=8); and whole-body passive heat stress followed by cycling (Study 2, n=8). We quantified femoral artery shear rates (SRs) and arterial and venous platelet (PMV – CD41+) and endothelial microvesicles (EMV – CD62E+). In Study 1, mild passive heat stress whilst one leg remained cooled did not affect [microvesicle] (P≥0.05). Single-leg knee extensor exercise increased active leg SRs by ~12-fold and increased arterial and venous [PMVs] by 2 to 3-fold, even in the non-exercising contralateral leg (P<0.05). In study 2, moderate whole-body passive heat stress increased arterial [PMV] compared to baseline (Mean±SE, from 19.9±1.5 to 35.5±5.4 PMV.µl-1.103, P<0.05), and cycling with heat stress increased [PMV] further in the venous circulation (from 27.5±2.2 at baseline to 57.5±7.2 PMV.µl-1.103 during cycling with heat stress, P<0.05), with a tendency for increased appearance of PMV across exercising limbs. Taken together, these findings demonstrate that whole-body heat stress may increase arterial [PMV], and intense exercise engaging either large or small muscle mass promote PMV formation locally and systemically, with no influence upon [EMV]. Local shear stress, however, does not appear to be the major stimulus modulating PMV formation in healthy humans.