Figure 6. The relationship of plasma AVP concentration to changes in plasma osmolality during controlled hypertonic stimulation. AVP concentration determined during progressive hypertonicity induced by infusion of 855 mmol/l saline in a group of healthy adults. Increases in plasma osmolality increase plasma AVP concentrations in a linear manner, defined by the function, plasma AVP = 0.43 (plasma osmolality – 284), r = +0.96. The abscissal intercept of this regression line indicates the mean ‘osmotic threshold’ for AVP release: the mean plasma osmolality above which plasma AVP starts to increase. The shaded area represents the range of normal response. LD represents the limit of detection of the assay, 0.3 pmol/l.