AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 4 892-R897, Copyright © 1989 by American Physiological Society
Osmotic thresholds for AVP release with the use of plasma and urine AVP and free water clearance
A. M. Moses
Veterans Administration Medical Center, Syracuse, New York.
Eleven hydrated normal subjects were infused with hypertonic saline so that
plasma osmolalities (POsmol) ranged from 280 to 306 mosmol/kg. Linear
relationships were calculated between POsmol and plasma and urine arginine
vasopressin (AVP) in the 11 individual subjects. There was an excellent
linear correlation between POsmol and plasma and urine AVP, with the latter
as concentration or rate of excretion. The highest correlation coefficient
occurred when urine AVP was expressed as microunits of AVP per 100
milliliters of glomerular filtrate. The smallest coefficient of variation
of the slopes occurred when urine AVP was expressed as microunits of AVP
per minute. The osmotic thresholds obtained by abscissal intercepts from
relating POsmol to urine AVP per minute or per 100 milliliters of
glomerular filtrate were 285.9 and 285.5 mosmol/kg, respectively. These
values did not differ from the mean osmotic threshold obtained by
traditional free water clearance changes (285.8 mosmol/kg). Analysis of the
relationship between plasma osmolality and plasma AVP resulted in the
greatest variation in slope and osmotic threshold, with the latter being
significantly lower than that obtained by free water clearance changes. The
data also demonstrated a much more rapid rise of urine than of plasma AVP
under the stated conditions of osmotic stimulation.
