RESUMEN
Urine concentration and dilution were examined in healthy young Burmese subjects in 21 exercise and 29 rest experiments carried out during the monsoon and the cooler period of the year. The effect of deprivation of fluid with and without exogenous vasopressin and that of forced fluid intake were studied. During 22 hours of dehydration at rest the average urine osmolality of the 2 hr collection period ranged between 600 and 1100 mOsm/1 and in few samples was the osmolality above 1200 mOsm/1. Exogenous vasopressin did not raise the urine osmolality significantly. Urine osmolalities suring exercise without fluid intake were lower than those attained during rest. Maximal free water reabsorption was within the normal range. In all dehydration experiments extremely low urea clearance values were found. Experiments with forced fluid intake produced maximally dilute urines indicating efficient diluting mechanism of the kidney in Burmese subjects in case of positive water balance. Low urea load and possibly low GFR are suspected as causes of the inability of subjects to achieve higher urine concentration.