The role of β-adrenergic receptors in mediating exercise hyperemia during incremental single-leg knee extension in young males and females.

Abstract

Previous research has identified a role for β-adrenergic receptors in mediating sex differences in blood pressure regulation at rest. β-receptors are also involved in the exercise hyperemia response during low-intensity small muscle mass exercise in males. However, less is known about β-adrenergic receptors in mediating local exercise hyperemia response during graded large muscle mass exercise in young males and females. We compared steady-state cardiorespiratory responses, leg blood flow (Q̇_LEG), and leg vascular conductance (LVC) in 16 participants (8 females) at rest and during incremental knee extension exercise with and without complete nonselective β-adrenergic blockade using propranolol. Propranolol reduced absolute heart rate (HR), Q̇_LEG, and LVC responses during exercise. Females had greater absolute increases in HR and lower absolute Q̇_LEG and LVC during exercise. However, Q̇_LEG and LVC responses to incremental exercise were not different by sex or propranolol, even after normalizing for differences in estimated quadriceps muscle mass. Females were also found to have greater dilation of the femoral artery, which was blunted to a greater extent with propranolol compared with males at absolute exercise intensities. In conclusion, β-adrenergic receptors did not play an important role in mediating the overall exercise hyperemia response in males or females, as the cardiovascular system prioritizes the preservation of oxygen delivery to the exercising muscle. However, β₂-adrenergic receptors appear to play a distinct role in mediating sex differences in changes to vascular tone during exercise.NEW & NOTEWORTHY We examined the role of beta-adrenergic receptors (β-ARs) in mediating exercise hyperemia in males and females. No sex differences in leg blood flow or leg vascular conductance, but females exhibited greater dilation of the femoral artery (FA), and β-AR blockade blunted FA dilation in females at absolute exercise intensities. Findings highlight that exercise hyperemia is not reliant on β-ARs and suggest females rely more on β-ARs in mediating vascular tone during exercise.