Part of “CHAPTER 25 – PHYSIOLOGY OF VASOPRESSIN, OXYTOCIN, AND THIRST“

In healthy adults, vasopressin and oxytocin distribute rapidly into a space roughly equivalent in volume to the extracellular compartment.12,39 This initial mixing phase has a half-time of 4 to 8 minutes and is virtually complete in 10 to 15 minutes. This rapid mixing phase is followed by a second, slower decline that probably corresponds to the metabolic or irreversible phase of clearance. The half-time of the metabolic phase varies considerably from person to person but is in the range of 10 to 20 minutes. The metabolic clearance rate determined by steady-state as well as non–steady-state methods is largely independent of the plasma concentration within the physiologic range (ranging from 5 to 20 mL/kg per minute for vasopressin12,39 and from 10 to 23 mL/kg per minute for oxytocin).40 In pregnant women, the metabolic clearance rate of vasopressin is increased threefold to fourfold.21