Renal Vasoconstriction in Response to Muscle Mechanoreflex Activation Similar in Young and Older Healthy Humans

Abstract

Aging augments the renal vasoconstrictor response to handgrip exercise in humans (Momen et al., 2004). Muscle mechanoreflex activation causes renal vasoconstriction in young healthy humans (Momen et al., 2003). However, the effect of aging on the renal vasoconstrictor response to muscle mechanoreflex activation in healthy humans is not known. Therefore, 11 young (Young; 5 men; mean ± standard error of the mean 26±1y) and 10 older (Older; 4 men; 62±1y) healthy subjects underwent 3-min passive calf muscle stretch during lower-limb circulatory occlusion at rest, once following 1.5-min one-legged isometric calf exercise at 70% maximal voluntary contraction (MVC; local metabolite accumulation), and once with no prior exercise (0% MVC control). Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as mean arterial blood pressure (MAP; Finometer) divided by renal blood flow velocity (Doppler ultrasound). Statistical analysis involved repeated measures analysis of variance with factors including age, trial, and phase of trial. All variables were similar at baseline between trials and ages, except MAP was higher in Older than Young (P<0.05). Stretch significantly increased RVR from pre-stretch levels in both Young and Older, and 0% and 70% (P<0.05). The stretch-induced increase in RVR was similar in both Young and Older, and 0% and 70% (Young: 0% 9±3% and 70% 8±3%; Older 0% 14±4% and 70% 13±2%). In conclusion, the renal vasoconstrictor response to muscle mechanoreflex activation is similar in young and older healthy humans, in both the presence and absence of local metabolites. Supported by National Institutes of Health grants P01 HL096570 and UL1 TR000127 (LIS).