Effect of an exercise-heat acclimation program on body fluid regulatory responses to dehydration in older men
Takamata, A.; Ito, T.; Yaegashi, K.; Takamiya, H.; Maegawa, Y.; Itoh, T.; Greenleaf, J.E.; Morimoto, T.
American Journal of Physiology 277(4): R1041-R1050
1999
ISSN/ISBN: 0002-9513 PMID: 10516243 Document Number: 504577
We examined if an exercise-heat acclimation program improves body fluid regulatory function in older subjects, as has been reported in younger subjects. Nine older (Old; 70 ± 3 yr) and six younger (Young; 25 ± 3 yr) male subjects participated in the study. Body fluid regulatory responses to an acute thermal dehydration challenge were examined before and after the 6-day acclimation session. Acute dehydration was produced by intermittent light exercise 5% (P < 0.05) in Young subjects but not in Old. The body fluid loss during dehydration in the postacclimation test was similar to that in the preacclimation in Young and Old. The fractional recovery of lost fluid volume during rehydration increased in Young (by 80 ± 9%; P < 0.05) but not in Old (by only 34 ± 5%; NS). The improved recovery from dehydration in Young was mainly due to increased fluid intake with a small increase in the fluid retention fraction. The greater involuntary dehydration (greater fluid deficit) in Old was accompanied by reduced plasma vasopressin and aldosterone concentrations, renin activity, and subjective thirst rating (P < 0.05, Young vs. Old). Thus older people have reduced ability to facilitate body fluid regulatory function by exercise-heat acclimation, which might be involved in attenuation of the acclimation-induced increase in body fluid volume. Reprinted by permission of the publisher.