Rats heterozygous for hypothalamic diabetes insipidus (Brattleboro strain) and normal rats of the same strain were subjected to 4 days of water deprivation and 5 days of subsequent rehydration. Pituitary vasopressin depletion was 57 % as rapid in the rats heterozygous for diabetes insipidus as in normal rats even though the osmotic stimulus to vasopressin release was greater. The heterozygotes excreted a greater volume of more dilute urine throughout the period of dehydration. Pituitary vasopressin reaccumulation in the abnormal rats during rehydration was only 38% of the rate for the normal rats. There was no dissociation between biologically and immunologically measurable pituitary vasopressin in the rats heterozygous for diabetes insipidus at any time period. The data indicate that bhe defect in the Brattleboro strain of diabetes insipidus rats is one involving both synthesis and release of vasopressin, with only the synthesis defect being apparent in the homozygous rat. The heterozygous rat appears to represent a partial expression of the abnormality and allows demonstration of the abnormal release mechanism as well as the defective synthesis.
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