Aerobic physical training and alterations in pressor response during norepinephrine infusion: a controlled single-subject experiment.

To test the influence of aerobic physical training on pressor response to infused norepinephrine, the present study utilized a single subject A-B-A-B withdrawal design consisting of 9-week alternating sedentary and aerobic phases (S1, A1, S2, A2). During each 9-week phase the subject underwent infusions every 3 weeks, consisting of saline, low-dose and high-dose norepinephrine (Low-NE, High-NE). Heart rate and mean arterial blood pressure were monitored continuously; resting platelet and plasma catecholamines were also measured. Infusions were conducted 48 h from the most recent exercise bout to minimize residual effects of acute exercise. Fitness level was confirmed by VO2max during graded exercise testing at the conclusion of each 9-week phase. Blood pressure during saline did not differ between aerobic and sedentary phases. However, in all but one comparison, aerobic fitness was associated with a highly significant reduction in pressor response during Low-NE as well as High-NE. Plasma norepinephrine was higher during the two aerobic phases; platelet catecholamines and plasma epinephrine showed no reliable association with fitness. Results for this subject support an attenuation of pressor response associated with aerobic conditioning.