Conboy EE, Fogelman AE, Sauder CL, Ray CA. Endurance training reduces renal vasoconstriction to orthostatic stress. Am J Physiol Renal Physiol 298: F279 -F284, 2010. First published November 18, 2009 doi:10.1152/ajprenal.00447.2009.-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°head-up tilt (HUT) test before and after 8 wk of endurance training in eight healthy sedentary subjects (26 Ϯ 1 yrs). Training elicited a 21 Ϯ 3% increase in peak oxygen uptake (V O2peak) and a reduction in heart rate at rest of 8 Ϯ 2 beats/min. During HUT, heart rate progressively increased (ϳ20 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 (⌬14 Ϯ 5 cm/s) and renal vascular conductance (⌬22 Ϯ 7%) decreased during HUT, whereas after training renal blood flow velocity (⌬2 Ϯ 5 cm/s) and renal vascular conductance (⌬1 Ϯ 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.renal vascular conductance; head-up tilt CARDIAC OUTPUT DECLINES ϳ20% when humans assume an upright posture. Therefore, increases in peripheral resistance must occur to maintain blood pressure during standing. The renal vasculature is one of the most important vascular beds for increasing total peripheral resistance upon standing (17). Renal vascular resistance has been shown to increase ϳ30% during head-up tilt (HUT) (8,15). Another important role of the renal vasculature is observed during exercise, when renal and splanchnic vasoconstriction counteracts the vasodilation of the skeletal muscle to minimize a decrease in blood pressure (16).Some previous cross-sectional studies suggest that highly trained endurance athletes appear to be more susceptible to orthostatic intolerance than healthy sedentary individuals. It has been hypothesized that this increased susceptibility to orthostatic intolerance could be caused by either increased aerobic capacity or a hereditary predisposition for both increased aerobic capacity and orthostatic intolerance. Although there is evidence to support the hypothesis that increased aerobic capacity is associated with orthostatic intolerance, a mechanism for this association is equivocal (4).It has been established that trained humans and animals exhibit less vasoconstriction in both splanchnic and renal vasculature in response to the same acute dynamic exercise modality with...

Aerobic exercise training increases maximal sweat capacity and sweat responses at a given internal temperature. However, the mechanisms underlying these effects are unknown. The purpose of this study was to determine if aerobic exercise training improves in vivo cholinergic sensitivity and responsiveness of eccrine sweat glands. Eleven previously sedentary subjects were tested before and after 8 weeks of aerobic training consisting of 4 bouts of exercise per week that elicited an ~20% increase in peak oxygen uptake. In vivo cholinergic sensitivity and responsiveness were determined by dose‐response curves of acetylcholine (ACh) to sweat secretion rate on two forearm sites. ACh was administered via intradermal microdialysis while measuring cutaneous water loss (capacitance hygrometry) directly above the microdialysis membrane. Exercise training did not alter the number of cholinergic activated sweat glands or the dose‐response derived ED50 (2.0±0.1 to 2.1±0.1 ‐logM dose of ACh; P>0.05). However, the maximal response to the highest dose of ACh was greater after exercise training (0.84±0.11 to 1.16±0.21 mg/cm2/min, P<0.05). These data indicate that 8 weeks of aerobic exercise training does not increase in vivo cholinergic sensitivity as indicated by the ED50 but does increase maximal in vivo cholinergic responsiveness of human eccrine sweat glands. Support: HL77670, AG24420, M01 RR10732, C06

A possible mechanism for exercise training‐induced orthostatic intolerance is attenuation of the vestibulosympathetic reflex due to constant stimulation of the otolith organs during running. We tested the hypothesis that 8 weeks of endurance training will attenuate the vestibulosympathetic reflex in runners, but not stationary bikers. Arterial blood pressure, heart rate, calf blood flow, and muscle sympathetic nerve activity (MSNA) were recorded in healthy, sedentary, prone subjects (25±1 yr) at baseline and during head‐down rotation (HDR) before and after 8 weeks of endurance training. Subjects were assigned to running (n=13), stationary biking (n=12), or time control (n=12) groups. HDR increased MSNA and decreased calf vascular conductance (CVC) significantly in all groups before training. In contrast, after training MSNA did not increase (p>0.05) during HDR in runners (Δ2±1 bursts/min from baseline), but did in bikers and controls (Δ5±1 and Δ4±2 bursts/min, respectively; p<0.05). Furthermore, CVC did not decrease from baseline with HDR in runners, but decreased in bikers and controls (p<0.001). These data suggest an attenuation of the vestibulosympathetic reflex in endurance‐trained runners, but not stationary bikers. This is the first study to suggest that endurance running decreases the sensitivity of the otolith organs to changes in gravitational inputs. NIH info:ddbj-emblgenbank/DC006459, info:ddbj-emblgenbank/HL077670, and MO1RR10732