The effect of sex on the isolated and combined α‐ and β‐adrenergic control of blood flow during handgrip in adults at high altitude: An exploratory study

This study examined how sex influences blood flow during exercise at altitude and relative contributions of adrenergic mechanisms. Thirteen participants (8 M/5F) were tested at low and high altitude (days 3–11). Participants performed rhythmic handgrip for 3 min at 25% maximal voluntary contraction during local infusions of saline, propranolol (β-adrenergic blockade), and phentolamine with propranolol (α-β-adrenergic blockade). Doppler ultrasound was used to examine brachial artery blood flow (FBF) and calculate forearm vascular conductance (FVC). Resting FBF and FVC were higher in males compared to females across all conditions (p = 0.024; p = 0.025, respectively). Blockade condition significantly altered FBF and FVC (p < 0.001 for both) but there was no effect of altitude (p = 0.330; p = 0.718, respectively). During exercise, ΔFBF was influenced by condition (p < 0.001), but not by sex (p = 0.696) or altitude (p = 0.813). Similarly, ΔFVC was different across conditions (control: 9.4 ± 2.3 mL/min/mmHg/FAV; β-blockade: 11.4 ± 12.8 mL/min/mmHg/FAV; α-β-blockade: 3.9 ± 1.1 mL/min/mmHg/FAV; p < 0.001), with no effect of sex (p = 0.646) or altitude (p = 0.889). These results suggest males and females do not respond differently to exercise at altitude, and light-intensity exercise hyperemia may be preserved during early acclimatization. α-adrenergic receptors appear important for exercising blood flow, but β-adrenergic receptors may not be critical in this response.