(604.3) Endothelial Sensitivity to Exercise-Induced Shear Rate in Pre- and Post-Menopausal Females and in Males

Poster Board Number: E470

Amélie Debray (Institut de Cardiologie de Montréal, Institut de Cardiologie de Montréal, Institut de Cardiologie de Montréal), Nicholas Ravanelli (Lakehead University), Hugo Gravel (Université de Montréal, Université de Montréal), Audrey-Ann Bartlett (Institut de Cardiologie de Montréal, Institut de Cardiologie de Montréal), Charlotte Usselman (McGill University), Louis Bherer (Institut de Cardiologie de Montréal, Institut de Cardiologie de Montréal), Daniel Gagnon (Institut de Cardiologie de Montréal, Institut de Cardiologie de Montréal)

Background: Post-menopausal females appear resistant to the beneficial effects of exercise on endothelial function. Repeated increases in shear stress are considered important mediators of exercise-induced improvements in endothelial function. It is therefore possible that endothelial sensitivity to shear stress is reduced in post-menopausal females, thereby blunting endothelial adaptations to exercise training. The objective of this retrospective analysis was to test the hypothesis that post-menopausal females exhibit a lower endothelial sensitivity to exercise-induced shear rate relative to pre-menopausal females and age-matched males.

Methods: Five pre- (48 ± 1 yrs) and fifteen post- (65 ± 10 yrs) menopausal females, and five males (67 ± 5 yrs) performed 4-min rhythmic handgrip exercise bouts. Ten participants (6 post and 6 males) exercised at 20%, 40%, 60% and 80% of maximal voluntary contraction, and 15 participants (5 pre, 9 post and 2 males) exercised at 3 kg, 6 kg and 9 kg. The contraction/relaxation cycle was 2-sec/3-sec and each bout was separated by 10 min of rest. Brachial artery diameter and blood velocity were measured using high-resolution ultrasound and analyzed using edge-detection software. Endothelial sensitivity to exercise-induced shear rate was quantified as the slope of the relationship between brachial artery dilation (% change from baseline) and shear rate (in s-1).

Results: Baseline diameter was greater in males (4.68 ± 0.55 mm) compared with post- (3.24 ± 0.53 mm, plt;0.01) and pre- (3.55 ± 0.19 mm, plt;0.01) menopausal females. The rhythmic handgrip protocols elicited net shear rates that ranged between 38 s-1 and 392 s-1. A positive correlation was observed between brachial artery dilation and net shear rate in males (r=0.66, plt;0.01), and post-menopausal females (r=0.38; plt;0.01), but not in pre-menopausal females (r=-0.25, p=0.36). Endothelial sensitivity to exercise-induced shear rate did not differ between pre- (0.037 ± 0.120 %/s-1) and post- (0.069 ± 0.081 %/s-1, pgt;0.99) menopausal females, between pre-menopausal females (0.037 ± 0.120 %/s-1) and males (0.027 ± 0.055 %/s-1, pgt;0.99), or between post-menopausal females (0.069 ± 0.081 %/s-1) and males (0.027 ± 0.055 %/s-1, pgt;0.99).

Conclusion: These results suggest that post-menopausal females do not demonstrate a reduced endothelial sensitivity to exercise-induced shear rate compared with pre-menopausal females as well as with males of similar age.

Canadian Institutes of Health Research, HABISAN (Handicap Biologie Santamp;eacute;) Program, Regional Council of Nouvelle Aquitaine.