Absence of post exercise hypotension and sympathoinhibition in normal subjects: additional evidence for increased sympathetic outflow in borderline hypertension

OBJECTIVE: In young men (mean age 25 years) with borderline hypertension the authors have documented a reduction in systolic blood pressure and muscle sympathetic nerve activity 60 mins after 45 mins of submaximal treadmill exercise. The aim of this study was to determine if post exercise hypotension occurs in normotensive young men, and if so, if it is accompanied by a decrease in sympathetic nerve activity. DESIGN: Replicating a previous protocol, the authors recorded blood pressure, heart rate, plasma noradrenaline and muscle sympathetic nerve activity (microneurography; peroneal nerve) before and 60 mins after submaximal treadmill exercise. SUBJECTS: Ten healthy male volunteers (mean age 28 +/- 5 years). INTERVENTION: Forty-five minutes of treadmill exercise at 70% of resting heart rate reserve. MAIN RESULTS: In contrast to borderline hypertensive subjects, prior exercise had no effect on either systolic or diastolic blood pressure or muscle sympathetic nerve activity in healthy volunteers. Plasma noradrenaline concentrations were similar before and after exercise. Resting heart rate (56 +/- 3 versus 70 +/- 3 beats/min; P less than 0.002), and sympathetic burst frequency (10 +/- 4 versus 20 +/- 2 bursts/min; P = 0.026) were lower in normal than in borderline hypertensive men. CONCLUSIONS: At rest, discharge to muscle sympathetic nerves is increased in young borderline hypertensive men; and blood pressure and sympathetic nerve activity are decreased after exercise in borderline hypertensive but not normotensive men. These observations suggest that the depressor response to prolonged rhythmic exercise in young men with borderline hypertension may be due in part to transient suppression of augmented central sympathetic outflow.