The sweat glands maximum ion reabsorption rates following heat acclimation in healthy older adults.

Gerrett, N; Amano, T; Inoue, Y; Kondo, N

NEW FINDINGS What is the central question to this study? Do the sweat glands maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations? What is the main finding and its importance? Sweat glands maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals. ABSTRACT We examined whether the eccrine sweat glands ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65 yrs) completed a controlled hyperthermic (+0.9˚C rectal temperature, Tre ) HA protocol for 9 non-consecutive days. Participants completed a passive heat stress test (lower leg 42˚C water submersion) pre-HA and post-HA to assess physiological regulation of sweat glands ions reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7-day decay. During passive heating, the Tb thresholds for sweat onset on the chest and forearm were lowered after HA (P < 0.05). However, neither sweat sensitivity (i.e. the slope), the SR at a given Tre , nor gross sweat loss improved after HA (P > 0.05). Any changes observed were lost during the decay. Pilocarpine-induced sudomotor responses to iontophoresis did not change after HA (P ≥ 0.801). Maximum ion reabsorption rate was only enhanced at the chest (P = 0.001) despite unaltered aldosterone concentration after HA. The data suggests that this adaptation is lost after 7-days decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat glands ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults. This article is protected by copyright. All rights reserved.