Plasma Oxytocin Concentrations in a Pregnant Woman with Total Vasopressin Deficiency

Plasma concentrations of oxytocin and vasopressin were determined by radioimmunoassay in a woman with clinical diabetes insipidus. Plasma oxytocin levels were normal and ranged from less than 0.25 µU/ml to 76 µU/ml during the last month of pregnancy and during spontaneous labor. Vasopressin requirements did not change during pregnancy. Unexplained vasopressin resistance and massive diuresis occurred early in the postpartum period. Plasma vasopressin concentrations were undetectable in the nonpregnant state. The documentation of normal oxytocin production and total vasopressin deficiency suggests that an anatomic defect is unlikely to cause this disorder unless it is limited to axons and cell bodies containing vasopressin and not oxytocin.