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

This study tested the hypothesis that passive leg heating attenuates a-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 a1-adrenoreceptor agonist, phenylephrine (PE, 0.025 to 0.8 µg kg¿1 min¿1) and an a2-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