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Evidence for altered -adrenoreceptor responsiveness after a single bout of maximal exercise

¹United States Army Institute of Surgical Research, Fort Sam Houston 78234; ²Professional Performance Development Group, Inc., San Antonio 78240; and ³Rothe Development, Inc., San Antonio, Texas 78222

Submitted 5 February 2003 ; accepted in final form 22 March 2003

We studied hemodynamic responses to - and -receptor agonists in eight men to test the hypothesis that adrenoreceptor responsiveness is altered within 24 h of the performance of maximal exercise. Adrenoreceptor responsiveness was tested under two experimental conditions (with and without maximal exercise). Adrenoreceptor tests were performed 24 h after each subject performed graded upright cycle ergometry to volitional exhaustion. The 2 test days (experimental conditions) were separated by at least 1 wk, and the order of exercise and no-exercise conditions was counterbalanced. Steady-state graded infusions of phenylephrine (PE) and isoproterenol (Iso) were used to assess - and -adrenoreceptor responsiveness, respectively. Slopes calculated from linear regressions between Iso and PE doses and changes in heart rate, blood pressure, and leg vascular resistance for each subject were used as an index of - and -adrenoreceptor responsiveness. The slope of the relationship between heart rate and Iso with maximal exercise was 1,773 ± 164 beats · µg^–1 · kg^–1 · min^–1 compared with 1,987 ± 142 beats · µg^–1 · kg^–1 · min^–1 without exercise (P = 0.158), whereas the slopes of the relationship between vascular resistance to Iso were -438 ± 123 peripheral resistance units (PRU) · µg^–1 · kg^–1 · min^–1 with maximal exercise and -429 ± 105 ·µg^–1·kg^–1·min^–1 without exercise (P = 0.904). Maximal exercise was associated with greater (P < 0.05) vascular resistance (15.1 ± 2.8 PRU·µg^–1·kg^–1· min^–1) and mean arterial blood pressure (15.8 ± 2.1 mmHg · µg^–1 · kg^–1 · min^–1) responses to PE infusion compared with no exercise (9.0 ± 2.0 PRU · µg^–1 · kg^–1 · min^–1 and 10.9 ± 2.0 mmHg · µg^–1 · kg^–1 · min^–1, respectively). These results provide evidence that a single bout of maximal exercise increases ₁-adrenoreceptor responsiveness within 24 h without affecting -cardiac and vascular adrenoreceptor responses.

autonomic function; sympathetic; heart rate; blood pressure; baroreflex; vascular resistance

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