Inappropriate vasopressin secretion in two dogs.

Two dogs with hyponatremia due to inappropriate arginine vasopressin (AVP) secretion are described. Threshold and sensitivity of AVP secretion were investigated by increasing plasma osmolality with hypertonic saline infusion. In one dog, osmoregulation of AVP secretion occurred at normal sensitivity but at a low threshold. The other dog had a relatively high plasma AVP concentration under (resting) hypotonic conditions with an otherwise normal response to increasing plasma tonicity. In the absence of evidence for associated disease, it is suggested that both dogs have an idiopathic form of the syndrome of inappropriate AVP secretion.