The regulation of antidiuretic hormone release in man: I. Effects of change in position and ambient temperature on blood ADH levels.

It has been postulated that alterations in the intravascular distribution of blood affect antidiuretic hormone (ADH) secretion in man. The studies reported here were designed to alter blood distribution by thermal and by positional change to test this thesis.HUMAN BLOOD ADH LEVELS HAVE BEEN SHOWN TO VARY WITH POSITION: a mean value of 0.4 +/- 0.6 (SD) muU/ml was obtained while the subject was supine, a value of 1.4 +/- 0.7 muU/ml while sitting, and 3.1 +/- 1.5 muU/ml while standing. In 79 control subjects, sitting comfortably for 30 min in a normal environment, a blood ADH level of 1.65 +/- 0.63 muU/ml was found. It is suggested that subjects assume this position during experiments in which blood is drawn for measurement of ADH levels.In eight seated subjects the ADH level rose from 1.6 +/- 0.4 to 5.2 +/- 0.8 muU/ml after a 2 hr exposure at 50 degrees C and fell to 1.0 +/- 0.26 muU/ml within 15 min at 26 degrees C.Six subjects with a mean ADH level of 2.2 +/- 0.58 muU/ml sat quietly in the cold (13 degrees C) for 1 hr, and the ADH level fell to 1.2 +/- 0.36 muU/ml. After 15 min at 26 degrees C, the level rose to 3.1 +/- 0.78 muU/ml. The serum sodium and osmolal concentrations remained constant during all studies.Water, sodium, and total solute excretion decreased during exposure to the heat, whereas the urine to plasma (U/P) osmolal ratio increased. During cold exposure, water, sodium, and total solute excretion increased, and there was a decrease in the U/P osmolal ratio.These data are interpreted as indicating that changes in activity of intrathoracic stretch receptors, in response to redistribution of blood, alter ADH secretion independently of changes in serum osmolality. The rapidity of change of blood ADH concentration indicates a great sensitivity and a prime functional role for the "volume receptors" in the regulation of ADH secretion.