Plasma Osmolality and Plasma Vasopressin	

Under normal circumstances, healthy individuals maintain their plasma osmolality within the range 282–295m osmol/kg, with plasma vasopressin concentrations varying between 0.3 and 4pmol/l, thus allowing the formation of maximally dilute and concentrated urine, respectively. The relationship between plasma vasopressin (pAVP) and plasma osmolality (pOS) is linear, the average regression line being defined by the function:

pAVP=0.41 (pOS-284), r=0.96, P<0.001.

The slope of the line is a measure of the sensitivity of the osmoreceptor and vasopressin-releasing unit. The abscissal intercept defines the mean theoretical threshold for vasopressin release.