LAUSR

We sought to investigate whether the β-adrenergic receptors play a pivotal role in sex-related differences in arterial blood pressure (BP) regulation during isometric exercise. Sixteen volunteers (8 women) performed 2 min of ischemic isometric handgrip exercise (IHE) and 2 min of post exercise circulatory occlusion (PECO). Heart rate (HR) and beat-to-beat arterial BP were continuously measured. Beat-to-beat estimates of stroke volume (ModelFlow) were obtained and matched with HR to calculate cardiac output (Q̇) and total peripheral resistance (TPR). Two trials were randomly conducted between placebo and non-selective β-adrenergic blockade (40mg propranolol). Under the placebo condition, the magnitude of the BP response in IHE was lower in women compared with men. During PECO, the BP remained elevated and the sex differences persisted. The β-blockade attenuated the BP response during IHE in men (∆ 57±4 mmHg vs ∆ 45±7 mmHg, P=0.025) due to a reduction in Q̇ (∆ 3.7±0.5 l/min vs ∆ 1.8±0.2 l/min, P=0.012) while TPR was not affected. In women, however, the BP response during IHE was unchanged (∆ 27±3 mmHg vs ∆ 28±3mmHg, P=0.889), despite attenuated Q̇ (∆ 2.7±0.4 l/min vs ∆ 1.3±0.2 l/min, P=0.012). These responses were mediated by a robust increase in TPR under β-blockade (∆-0.2±0.4 mmHg.L-1.min vs ∆ 2.2±0.7 mmHg.L-1.min, P=0.012). These findings demonstrate that the sex differences in arterial BP regulation during ischemic IHE are mediated by β-adrenergic receptors.