Plasma Neurophysin and Vasopressin in the Rat: Response to Adrenalectomy and Steroid Replacement*

Abstract

Impaired excretion of a water load is known to occur in adrenal insufficiency and to be corrected by administration of glucocorticoid. Such impairment has been related to either a loss of a permissive effect of glucocorticoids on the diluting segments of the nephron or to an alteration of release, turnover or action of antidiuretic hormone. Specific and sensitive RIA [radioimmunoassays] for arginine vasopressin and neurophysin were utilized to measure plasma and pituitary levels of neurohypophyseal peptides at baseline and after an intragastrically administered water load. Conscious, unanesthetized and nonstressed sham-operated, adrenalectomized and adrenalectomized prednisone-treated rats were studied. A significant elevation in vasopressin and neurophysin occurred in plasma of adrenalectomized rats maintained in a normal state of hydration. After water loading, the adrenalectomized rats diluted their plasma osmolality but had a decreased urinary volume, increased urinary osmolality, and elevated vasopressin and neurophysin in their plasma. In the pituitary, vasopressin and neurophysin were depleted in adrenalectomized rats, indicating increased secretion of these peptides. Elevated vasopressin in plasma may be an important factor in the incomplete water diuresis found in adrenal insufficiency.