Radioimmunoassay of urinary antidiuretic hormone in man: Response to water load and dehydration in normal subjects

A simple, efficient procedure for extracting and concentrating antidiuretic hormone (ADH) from urine has been coupled with a specific radioimmunoassay for ADH in order to quantitate urinary excretion of the hormone. Normal human subjects under conditions of normal activity and random hydration excreted a mean value of 28.9 mU ADH/24 hr, with excretion in 70% of the subjects ranging between 11- 30 mU/24 hr. No difference in hormone excretion was found in urine collected during waking hr and during sleep. In response to oral water loading, plasma osmolality fell to 269-283 mOsm/kg and urinary ADH excretion became undetectable during the peak of the diuresis in 19 of 22 subjects. Following 14 hr of fluid deprivation, plasma osmolality rose to a mean of 290.6 mOsm/kg and urinary ADH excretion rose from 1.00 ± 0.19 mU/hr to 2.74 ± 0.53 mU/hr. ADH excretion can be readily quantitated in normal subjects and appears to respond to alterations in plasma osmolality which affect ADH release from the posterior pituitary and thus is capable of serving as an effective means of assessing neurophypophyseal function in man.