α-Adrenergic vasoconstrictor responsiveness is preserved in the heated human leg

This study tested the hypothesis that passive leg heating attenuates α-adrenergic vasoconstriction within that limb. Femoral blood flow (FBF, femoral artery ultrasound Doppler) and femoral vascular conductance (FVC, FBF/mean arterial blood pressure), as well as calf muscle blood flow (CalfBF, ¹³³xenon) and calf vascular conductance (CalfVC) were measured during intra-arterial infusion of an α₁-adrenoreceptor agonist, phenylephrine (PE, 0.025 to 0.8 μg kg₋₁ min₋₁) and an α₂-adrenoreceptor agonist, BHT-933 (1.0 to 10 μg kg₋₁ min₋₁) during normothermia and passive leg heating (water-perfused pant leg). Passive leg heating (∼46◦C water temperature) increased FVC from 4.5 ± 0.5 to 11.9 ± 1.3 ml min₋₁ mmHg₋₁ (P <0.001). Interestingly, CalfBF (1.8±0.2 vs. 2.8±0.3mlmin₋₁ (100 g)₋₁) and CalfVC (2.0±0.3 vs. 3.9±0.5mlmin₋₁ (100 g)₋₁ mmHg₋₁ ×100) were also increased by this perturbation (P