The Effects of Elevated Circulating Prolactin in Rats with Hereditary Hypothalamic Diabetes Insipidus (Brattleboro Strain)*

Administration of ovine or rat PRL to animals, including man, has resulted in decreased urine volume and increased urine osmolality. Contamination of PRL preparations with vasopressin is the most likely explanation for the apparent antidiuretic effect. In this study, diabetes insipidus rats lacking vasopressin(homozygous Brattleboro rats) had extra anterior pituitary glands implanted under the kidney capsule, resulting in hyperprolactinemia. The urine of such rats was not more concentrated than that of unoperated littermates or sham-operated littermates with diabetes insipidus. In fact, hyperprolactinemic male rats produced even less concentrated urine than control rats. Furthermore, the hyperprolactinemic rats responded to exogenous vasopressin in a manner similar to normoprolactinemic rats. These studies provide strong evidence against an antidiuretic action of PRL in mammals.