The use of arginine vasopressin measurements in the polyuric dog.

The direct measurements of AVP during water deprivation and salt loading demonstrate the inability of the direct water deprivation test to distinguish accurately between several forms of polyuria. Polyuria and polydipsia are commonly formed disorders in the dog and can be caused by osmotic diuresis; deficient release of anti-diuretic hormone-arginine vasopressin (AVP); a decreased renal response to AVP; excessive water intake. The differentiation between these forms often requires a water deprivation test followed by administration of vasopressin. The latter test is an indirect one and relies upon changes in urinary concentration as index of vasopressin function. With this it is usually possible to differentiate total neurogenic diabetes insipidus and total nephrogenic diabetes insipidus. However, several dipsogenic forms and partial diabetes insipidus forms are still very difficult to distinguish from each other and only the direct measurement of plasma AVP (PAVP) can give conclusive information. The role of AVP in osmoregulation was investigated by measuring plasma osmolality (Posm) and PAVP during; hypertonic saline infusions; water deprivation in both healthy experimental dogs and in dogs with polyuria.