Submitted on March 19, 2009
Revised on June 9, 2009
Accepted on June 9, 2009
Interactive Effect of Aging and Local Muscle Heating on Renal Vasoconstriction During Isometric Handgrip
Nathan T Kuipers1, Charity L. Sauder, Matthew L. Kearney, and Chester A. Ray1*
1 Pennsylvania State University College of Medicine
* To whom correspondence should be addressed. E-mail: caray{at}psu.edu.
The purpose of the study was to determine the interactive effect of aging and forearm muscle heating on renal vascular conductance and muscle sympathetic nerve activity during ischemic isometric handgrip. A tube lined water-perfused sleeve was used to heat the forearm in twelve young (27 ± 1 yr) and nine older (63 ± 1 yr) subjects. Ischemic isometric handgrip was performed before and after heating. Muscle temperature (intramuscular thermistor) was 34.3 ± 0.2 ºC and 38.7 ± 0.1 ºC during normothermia and heating, respectively. At rest, heating had no effect on renal blood velocity (Doppler ultrasound) or renal vascular conductance in either group (young, n = 12; older, n = 8). Heating compared to normothermia caused a significantly greater increase in renal vasoconstriction during exercise and postexercise muscle ischemia (PEMI) in both groups. However, the increase in renal vasoconstriction during heating was greater in the older compared to the young subjects (18 ± 3% vs. 8 ± 3%). During handgrip, heating elicited greater increases in muscle sympathetic nerve activity (MSNA) responses in the older group (young, n = 12; older, n = 6), whereas, no statistical difference was observed between groups during PEMI. In summary, aging augments renal vascular responses to ischemic isometric handgrip during heating of the exercising muscle. The greater renal vasoconstriction was associated with augmented MSNA in the older subjects.
