ABSTRACT
Objective To investigate the effect of metoprolol and metoprolol combined with moderate inten-sity aerobic exercise on the sympathetic vasoconstriction response of skeletal muscle, functional sympatholysis and the exercise capacity of hypertensive men. Methods Thirty men with mild ( stage 1) essential hypertension were divi-ded into a drug group and an observation group. The drug group received only metoprolol while the observation group took metoprolol and performed aerobic exercise (intensity 50-70％ of VO2max, 30-45 min/time, 3-5 times/week) for 12 weeks. Before and after the experiment, the subjects' maximum oxygen uptake (VO2max), peak power (PP) as well as a rating of perceived exertion ( RPE) curve during exercise were determined using the graded exercise test. Forearm vascular conductance ( FVC) induced by the cold pressor test was measured using Doppler ultrasound at rest and during a handgrip exercise. Sympathetic vasoconstriction response was manifested by the rate of change in the conductance (％FVC) before and after the cold pressor test. Functional sympatholysis ( the ability of muscle contrac-tions to inhibit sympathetic vasoconstrictor response) was quantified using the difference in the ％FVC values (△％FVC) between the handgrip exercise and at rest. Results After the treatment,％FVC during the handgrip exercise was lower than at rest in the observation group.△％FVC had increased significantly, as had VO2max and PP. The RPE curve during a graded exercise test shifted to the right in the observation group, but there was no significant change in the other observations. In the drug group, PP had decreased significantly and the RPE curve had shifted to the left. Conclusion Metoprolol can better improve functional sympatholysis and enhance exercise capacity when it is com-bined with moderate intensity aerobic exercise. That will alleviate any exercise intolerance in men with mild hyperten-sion caused by taking metoprolol alone.
ABSTRACT
Objective To explore the effect of exercise on functional sympatholysis in rats modeling spontaneous hypertension and the role of the nitric oxide signal pathway. Methods Thirty Wistar rats with spontaneous hypertension were randomly divided into a sedentary group and an exercise group, each of 15, while another fifteen healthy rats acted as controls. The exercise group performed eight weeks of voluntary wheel run-ning exercise while the other two groups did not. The rats were instrumented to stimulate the lumbar sympathetic chain ( at 1 Hz, 2.5 Hz or 5 Hz) to induce vasoconstriction and the triceps surae muscle group was forced to contract by stimulating the tibial nerve electrically. The change in the femoral artery vascular conductance ( FAVC) in response to sympathetic stimulation was recorded at rest and during contraction. The functional sym-patholysis was calculated as the percentage difference in FAVC (△％FAVC) in response to sympathetic stimu-lation during muscular contraction and at rest (△％FAVC=％FAVC during contraction-％FAVC at rest) . After administration of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester ( L-NAME) , changes in FAVC were repeatedly determined. Results The average △％FAVC of the sedentary group was significantly lower than that of the control group at all stimulation frequencies, while the average △％FAVC in the exercise group was significantly higher than in the sedentary group. There were no significant differences between the exer-cise and control groups. After the administration of L-NAME, significant decrease was observed in the average△％FAVCs of the control and exercise groups, but there was no significant change in the sedentary group. Conclusion Voluntary exercise may improve functional sympatholysis in rats with spontaneous hypertension through improving NO-dependent signalling.