From Dog

HIsosthenuria in dogs is defined as a urine specific gravity (USG) > 1.030 and implies normal urine concetrating ability by the kidneys.

Urine concentration is determined by the action of vasopressin upon the principal cells of the cortical and medullary collecting ducts, and is dependent upon the presence of a hyperosmotic medullary interstitium.

Renal or systemic abnormalities may result in polyuria and hyposthenuria.