β-adrenergic receptors do not impact exercise hyperemia during rhythmic handgrip exercise in males and females

Sex differences in exercise hyperemia remain unclear, and the role of β-adrenergic receptors (β-AR) in this response is unknown. Accordingly, we examined the role of β-AR in modulating central and peripheral hemodynamic responses to rhythmic handgrip exercise in 10 females and 7 males under control conditions (CON) and during β-AR blockade with oral propranolol (PROP). Participants completed a low-intensity (10% MVC) and incremental (40, 80, 120 N) rhythmic handgrip exercise. Hemodynamic variables, including heart rate (HR), mean arterial pressure (MAP), brachial artery diameter (BA D ), forearm blood flow (Q̇ ARM ), and vascular conductance (VC ARM ) were assessed at baseline and during steady state exercise for each intensity. The overall hyperemia response was assessed as the slope of the relationship between Q̇ ARM and VC ARM over exercise intensity. β-AR blockade was achieved with two 80mg doses of oral HCl propranolol administered 7.5 and 1.5 hours prior to the PROP visit. β-adrenergic blockade reduced HR and absolute Q̇ ARM in males and females (both, p<0.05), but not MAP (p=0.49). The overall exercise hyperemia slope response for Q̇ ARM and VC ARM did not differ by sex or with β-AR blockade (both p>0.05), even after adjusting to maximal handgrip strength (both, p>0.05). The relative increase in BA D from baseline was blunted in females (p=0.03) but not males (p=0.96) during PROP. In conclusion, the exercise hyperemia response is preserved in males and females with systemic β-adrenergic receptor blockade. However, young females appear to have a greater reliance on β-AR relative to males in mediating macrovascular tone during exercise.