Changes in Neurohypophysial Proteins Induced by Dehydration and Ingestion of Saline1

Abstract

Sustained dehydration or prolonged ingestion of salt solution In rats resulted in marked changes in the appear -ance of the posterior lobe of the pituitary and an increase in its size and weight. Also, several protein components of the posterior pituitary decreased in concentration; with rehydration or replacement of saline with water they returned to normal. Similar changes were observed in pttuitaries from several other species, including the pig, dog, and rabbit. Peptide II, previously identified as a lipolytic factor in porcine pituitaries and which is the principal soluble protein component of the posterior pituitary, decreased most markedly with dehydration. It is suggested that in each species the homologous polypeptides which vary with the state of hydration constitute the "neurosecretory material." In rats with congenital diabetes insipidus (Brattleboro strain) the concentration of these peptides was greatly reduced and prolonged administration of exogenous vasopressin did not restore them to normal. The mutation results in a failure of synthesis of vasopressin; in some manner the synthesis of these peptides also is affected, indicating that the biosynthesis of both is intimately related. The binding of vasopressin to peptide n appeared to be ionic with studies using gel filtration.