The ADH-reserve capacity in Brattleboro rats.

: The water metabolism was studied in homo- and heterozygous Brattleboro rats suffering from hereditary hypothalamic diabetes insipidus. In homozygous Brattleboro rats the spontaneous water intake and urinary output and the diuretic reactions signficantly increased after water and salt loading. No antidiuretic activity was found in the urine, posterior pituitary or hypothalamus of these animals, and this state was not affected by hyperosmosis. For the heterozygous rats the spontaneous water intake and urinary output and the diuretic reaction exceed the respective control values, the posterior pituitary, the hypothalamus and the urine are of reduced antidiuretic activity and this activity is less mobilizable by hyperosmosis. It is concluded that the ADH-reserve deficiency is total in the homozygous Brattleboro rats, and partial in the heterozygotes. As a result of hyperosmosis, the vasopressin release is of a reduced extent, yet detectable in the heterozygotes.