Relationship of evaporative rates to serum Na*. K* and osmolarity in acute heat stress

[Xal, [K+], and osmohrity in acute heat stress. J, Appl. Physiol. 25(2): 14-Y-152. 1968.-Five unacclimatized nude male subjects were exposed for 4 hr to 43.3 C DB, 29 C WB, with and without rehydration. For 10 min of each 30 min subjects exercised at rates of 400-450 kg-m/min. Serum [Na+], [I?], and osmolarity were measured prior to and at 30-min in-tervals during heat exposure. Decreased rates of evaporative weight losses during dehydration were significantly correlated with A [Na+] and A osmolarity, but not with A [I?] or A w+l/cK+l>. A 0 smolarity did not correlate with A evapora-tive rates when influence of A [Na+] was arithmetically re-moved from osmolarity figures. Whether increased serum [Na+] affects sweat gland secretory or reabsorptive activity was not determined. Reductions in evaporative rates during dehydra-tion occurred within the 1st hr of heat exposure and such re-ductions probably reflect, in part, changes in serum [Na+]. dehydration; sweating; body fluids M ODERATE DEHYDRATION accompanied or followed by heat exposure reduced individual rates of sweating from levels existing with adequate salt and water replacemen