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

Convertino, Victor A. Evidence for altered -adrenoreceptor responsiveness after a single bout of maximal exercise. J Appl Physiol 95: 192–198, 2003. First published April 4, 2003; 10.1152/japplphysiol.00123.2003.—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 g 1 kg 1 min 1 compared with 1,987 142 beats g 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) g 1 kg 1 min 1 with maximal exercise and 429 105 g 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 g 1 kg 1 min 1) and mean arterial blood pressure (15.8 2.1 mmHg g 1 kg 1 min 1) responses to PE infusion compared with no exercise (9.0 2.0 PRU g 1 kg 1 min 1 and 10.9 2.0 mmHg g 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.