RESUMEN
Endurance training has been associated with increased orthostatic intolerance. The purpose of the present study was to test the hypothesis that endurance training reduces renal vasoconstriction to orthostatic stress. Blood pressure, heart rate, and renal blood flow velocity were measured during a 25-min 60 degrees head-up tilt (HUT) test before and after 8 wk of endurance training in eight healthy sedentary subjects (26 +/- 1 yrs). Training elicited a 21 +/- 3% increase in peak oxygen uptake (V(O(2)peak)) and a reduction in heart rate at rest of 8 +/- 2 beats/min. During HUT, heart rate progressively increased (approximately 20 beats/min) over the 25-min HUT trial both before and after training. Systolic arterial blood pressure during HUT was unchanged with training, whereas diastolic arterial blood pressure was lower at the end of HUT after training. Before training renal blood flow velocity (Delta14 +/- 5 cm/s) and renal vascular conductance (Delta22 +/- 7%) decreased during HUT, whereas after training renal blood flow velocity (Delta2 +/- 5 cm/s) and renal vascular conductance (Delta1 +/- 12%) did not change significantly during HUT. Renal blood flow velocity and vascular conductance responses to HUT did not change in control subjects during the 8-wk period. These results demonstrate that endurance training reduces renal vasoconstriction during an orthostatic challenge and may contribute to training-induced orthostatic intolerance.