Episodic secretion of arginine vasopressin

The plasma arginine vasopressin (pAVP) response to osmotic stimulation was studied in dogs and sheep by sampling at frequent intervals during steady-state dehydration and during water diuresis. Frequent sampling also was conducted after continuous infusion or bolus injection of 5 or 20 g/100 ml NaCl. A pulsatile pattern of pAVP was observed after such infusions or injections and in some animals after water deprivation. This pattern was not seen after water loading or in mildly dehydrated animals. The short term changes in pAVP during continuous infusion of 5 g/100 ml NaCl could not be correlated with variations in plasma tonicity. Rather, they appeared to reflect discontinuous hypothalamic posterior pituitary release of AVP. Thirst was evoked by a lower dose of 5 g/100 ml NaCl than was required for consistent stimulation of pAVP release, and the thirst response frequently was observed prior to the peak AVP response after bolus injection of 5 and 20 g/100 ml NaCl.