| Abstrakt: |
Cardiovascular control during exercise is regulated in part by reflex feedback from muscle afferent nerve fibres (McCloskey and Mitchell, 1972). Handgrip exercise causes renal vasoconstriction in humans (Middlekauff et al., 1997) and muscle mechanoreflex and metaboreflex activation can each cause renal vasoconstriction (Momen et al., 2003). However, it is unknown whether renal vasoconstriction occurs during calf exercise or the extent to which muscle mechanoreflex and metaboreflex activation contribute to this reflex. Therefore, this study examined renal vascular responses during isometric calf exercise, muscle mechanoreflex and/or metaboreflex activation in humans. Nine subjects (4 men, mean ± standard error of the mean 27 ± 1 y, 71 ± 3 kg, 1.72 ± 0.03 m) performed 1.5-min one-legged, isometric calf exercise at 70% maximal voluntary contraction (MVC), 3.5-min post-exercise circulatory occlusion (PECO) of the exercised leg and 3-min passive calf muscle stretch with continued occlusion. A 0% MVC (rest) control trial was also performed. Mean arterial blood pressure (MAP; Finometer), heart rate (HR; ECG) and renal blood flow velocity (RBFV; Doppler ultrasound) were measured. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as MAP / RBFV. Statistical analysis involved repeated measures ANOVA and paired samples t-tests. Baseline MAP, HR and RVR were similar between trials (84 ± 3 vs. 84 ± 3 mmHg, 62 ± 2 vs. 64 ± 2 b.min-1 and 1.48 ± 0.13 vs. 1.43 ± 0.09 arbitrary units for 0% and 70%, respectively). 70% exercise significantly increased MAP, HR and RVR above baseline and 0% (p<0.05; Table 1). After exercise, these values fell but PECO caused MAP and HR to remain significantly elevated from baseline (p<0.05), whereas RVR returned to resting levels. Stretch significantly increased MAP, HR and RVR from baseline in both 70% and 0% (p<0.05). In conclusion, these findings suggest that renal vasoconstriction occurs during isometric calf exercise in humans. Additionally, muscle mechanoreflex activation via calf stretch increased RVR, both in the presence and absence of local metabolite accumulation. Therefore, muscle mechanoreflex activation may contribute towards renal vasoconstriction occurring during calf exercise. [ABSTRACT FROM AUTHOR] |
