Sympathetic vasoconstrictor responsiveness is reduced by 5-day endurance training with enhanced baroreflex sensitivity in men

 

Kazunobu Okazaki¹, Yoshi-ichiro Kamijo¹, Shizue Masuki¹, Shigeki Ikegawa¹, Yoshiyuki Okada¹, Daisuke Yazawa¹, Takeki Hata², Yuji Shiba², Masafumi Takahashi², Uichi Ikeda², and Hiroshi Nose¹

¹Department of Sports Medical Sciences and ²Cardiovascular Medicine, Shinshu University Graduate School of Medicine, Matsumoto 390-8621, Japan

 

We tested the hypothesis that sympathetic vasoconstrictor responsiveness (VCR) in the trained muscles was reduced while baroreflex sensitivity (BRS) was enhanced after endurance training (ET). Ten young men (age, 21±2 (SD) yr) performed cycling exercise for 5 days (70%Vo_2peak, 30 min/day). Before and after ET, VCR in the forearm was determined from vascular conductance response (plethysmography) to α₁ and α₂ agonists, phenylephrine and dexmedetomidine, respectively, locally injected through a catheter in brachial artery. VCR in the calf was determined from vascular conductance response (plethysmography) to an increase in total muscle sympathetic nerve activity (MSNA, microneurography) evoked by rhythmic handgrip. We also determined sympathetic (total MSNA/diastolic blood pressure (BP)) and cardiac (heart rate/systolic BP) BRS by the modified Oxford method. We found that VCR in the calf decreased (-0.029 vs -0.012 AUxmin/SAU, P<0.05) while not in the forearm, and that both sympathetic (-0.98 vs -1.53 SAU/mmHg) and cardiac BRS (-0.59 vs -0.73 beats/min/mmHg, both P<0.02) were enhanced after training. Thus, ET by using lower extremities reduced VCR in the calf while not in the forearm with enhanced BRS, suggesting a close association between VCR and BRS.

 

Key words: exercise, autonomic nervous system, blood pressure