Inappropriate secretion of antidiuretic hormone in a dog.

Hyponatremia with simultaneous renal sodium loss was associated with the inappropriate secretion of antidiuretic hormone in a dog with heartworm disease. Antidiuresis caused expansion of extracellular fluid volume, which induced renal salt wasting and a negative sodium balance. The combination of water retention, salt wasting, and inactivation of intracellular solute contributes to the decrease in serum sodium concentration. Water intoxication due to hypotonicity of body gluids induced anorexia, depression, weakness, and incoordination.