Effects of Dehydration, Salt Depletion and Pitressin on Sweat Rate and Urine Flow

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 in the hot room during the first 4 hours and rested in a cool room 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 on 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. The men''s sweat rates were reduced about 20% by dehydration even though their skin temperatures were elevated. Sweating was reduced in the first hour of dehydration and when reduced during an experiment it could be elevated to normal within an hour by rapidly restoring the men''s water balance. In response to changes in water balance urine flow changed more slowly than sweat rate. Urine flow was lowest when the men were depleted of both water and salt. A marked diuresis resulted from water replacement during salt depletion. Pitressin given to fully hydrated men working in the heat produced a marked antidiuretic effect without altering sweat rate, thus indicating that the antidiuretic hormone was probably not responsible for the reduction of sweating in dehydration.