Does Priming Exercise Enhance Sympatholysis?

Priming exercise has been shown to enhance skeletal muscle blood flow during subsequent exercise. However, the mechanism responsible for the enhanced skeletal muscle blood flow has not been elucidated. PURPOSE: To investigate the hypothesis that heavy-intensity priming exercise would blunt sympathetic vasoconstrictor responsiveness and enhance contraction-mediated inhibition of sympathetic vasoconstriction (sympatholysis). METHODS: Young females (n = 13, 21 ± 3 years) and males (n = 8; 23 ± 2 years) performed alternate-leg knee-extension exercise where work was increased in a stepwise manner from passive exercise to moderate-intensity (30% peak power output, PPO, 7 min) preceded by either no priming exercise (MOD 1), or heavy-intensity (60% PPO, 6 min) priming exercise (MOD 2). A cold pressor test (CPT was performed at rest and during MOD 1 and MOD 2. Beat-by-beat blood pressure was measured via Finometer, and mean arterial pressure (MAP) was calculated. Leg blood flow (LBF) was measured using Doppler ultrasound, and femoral vascular conductance (FVC) was calculated as FVC = LBF⋅MAP-1. Sympathetic vasoconstrictor responsiveness was defined as the percent decrease in FVC (%αFVC) in response to the CPT. Sympatholysis was defined as the difference between the %αFVC response to the CPT at rest and during exercise. RESULTS: Sympathetic vasoconstrictor responsiveness at rest was not different (p > 0.05) between females (-45.1 ± 11.0%) and males (-40.5 ± 11.8%). During exercise, sympathetic vasoconstrictor responsiveness was blunted (p < 0.05) in both females and males. However, sympatholysis was greater (p < 0.05) in females compared with males during MOD 1 (Females: 23.5 ± 9.6, Males: 13.0 ± 7.6) and MOD 2 (Females: 23.2 ± 12.9, Males: 13.4 ± 6.6). Heavy-intensity priming exercise did not alter (p > 0.05) sympathetic vasoconstrictor responsiveness in females (MOD 1: -21.6 ± 7.7%; MOD 2: -21.9 ± 13.0%) or males (MOD 1: -27.5 ± 12.0%; MOD 2: -27.0 ± 11.1%). Sympatholysis was also unaffected (p > 0.05) by heavy-intensity priming exercise in females (MOD 1: 23.5 ± 9.6; MOD 2: 26.7 ± 9.0) and males (MOD 1: 13.0 ± 7.6; MOD 2: 13.4 ± 6.5). CONCLUSION: Heavy-intensity priming exercise did not blunt sympathetic vasoconstrictor responsiveness or enhance functional sympatholysis during subsequent moderate-intensity exercise. NSERC Canada