Output of NaCl by Sweat Glands and Kidneys in Relation to Dehydration and to Salt Depletion

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Abstract
Four 25-hour experiments were performed on each of 4 healthy young men. In all experiments the subjects started at 8 a.m. and walked on the treadmill (M.R. 190 calorie/ m2/hour) in the hot room (44.4[degree]C d.b.; 26.5[degree] w.b.) during the first 4 hours (sweat rate 1.1 kg/hour) and rested in a cool room (26[degree]C ) thereafter except for three 70-minute walks in the heat -beginning at 7, 12.5, and 24 hours, respectively, after the start. In one experiment the men maintained water and NaCl balance by drinking appropriate salt solutions throughout the experiment; in another experiment they maintained NaCl balance but were dehydrated by 3.1% of body weight in the first 4 hours and remained so through the 25th hour; in another they were dehydrated by 3.4% and depleted of an average of 157 meq of NaCl; and in still another they attempted to maintain water balance but were depleted of NaCl by an average of 169 meq. When salt balance was maintained and dehydration produced in the men there were significant increases of serum chloride, urinary chloride output in the first 14 hours and sweat chloride in the 14th and 25th hours as compared with the results in experiments in which both water and salt were maintained. In the salt depletion experiments serum chloride was increased slightly in dehydration but was decreased significantly when water was replaced. The salt conserving responses of both kidneys and sweat glands to salt depletion were definitely less marked when the men were dehydrated than when their water losses were replaced during the experiments.