Abstract
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.
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