In-exercise vascular shear rate during acute continuous and interval exercise: impact on endothelial function and miR-21

Background: Endothelial cell phenotype and endothelial function are regulated by hemodynamic forces, particularly wall shear stress (WSS). During a single bout of exercise, the specific exercise protocol can affect in-exercise WSS patterns, and consequently endothelial function. MicroRNAs might provide a biomarker of in-exercise WSS pattern, to indicate whether a specific exercise bout will have a positive effect on endothelial function. We evaluated the effect of acute interval (IT) and continuous (CON) in-exercise WSS patterns upon post-exercise endothelial function and circulating miR-21 expression. Methods and Results: 13 participants performed CON and 3 different IT exercise protocols matched for duration and intensity, on separate days. Oxygen uptake, heart rate and brachial artery blood flow were recorded throughout exercise. Brachial artery flow mediated dilation (FMD) was performed pre and 15 min post exercise. Plasma samples were acquired pre and 6 hours post exercise to determine miR-21 expression. In-exercise shear-rate (SR) patterns (a surrogate of WSS) differed according to the CON or IT work rate profile. In-exercise anterograde SR was greater in CON than IT (P<0.05), retrograde SR was equivalent between exercise protocols (P>0.05). Oscillatory shear index was higher during IT versus CON (P<0.05). Post-exercise FMD increased (pre 7.08±2.95, post 10.54±4.24%, P<0.05), whilst miR-21 expression was unchanged (pre 12.0±20.7 %cel-miR-39, post 11.1±19.3 %cel-miR-39, P>0.05); with no effect of exercise protocol (P>0.05). Conclusions: CON and IT exercise induced different SR patterns, but equivalent improvements in acute endothelial function. The absence of change in miR-21 expression suggests miR-21 is not a suitable biomarker of exercise-induced SR.