Functional sympatholysis: Do females do it better?

Our laboratory has recently shown that contraction-mediated inhibition of sympathetic vasoconstriction (sympatholysis) was enhanced in female compared with male rats. The purpose of this study was to investigate the hypothesis that sympatholysis would be enhanced in young females compared to young males during moderate (MOD)- and heavy (HVY)-intensity alternate-leg knee-extension (KE) exercise. Young (age 22±3), healthy adults (8 males, 8 females) performed a cold pressor test (CPT) at rest and during MOD- (30% of peak work rate) and HVY- (60% of peak work rate) intensity KE exercise. Blood pressure was measured via Finometer and mean arterial pressure (MAP) was calculated. Femoral blood flow (FBF) was measured using Doppler ultrasound, and femoral vascular conductance (FVC) was calculated as FVC=FBF·MAP^-1. Sympathetic vasoconstrictor responsiveness was defined as the percent decrease in FVC (%ΔFVC) in response to the CPT. Sympatholysis was defined as the difference between the %ΔFVC response to the CPT at rest and during exercise. Sympathetic vasoconstrictor responsiveness was not different (p>0.05) between males (-40.5±8.8%) and females (-46.0±10.4%) at rest. During exercise, sympathetic vasoconstrictor responsiveness was blunted in an exercise intensity-dependent manner in both males and females (p<0.001). However, sympatholysis was greater in females than in males during both MOD- (male: 13.2±6.2%; female: 26.7±9.0%; p<0.01) and HVY- (male: 25.3±7.3%; female: 36.1±8.0%; p<0.01) intensity exercise. Consistent with our previous findings in rats, sympatholysis was enhanced in human young females compared with males. These data provide further evidence that biological sex modulates sympathetic vascular control in the skeletal muscle vascular bed during exercise.