Effect of Hypophysectomy on Serum Dopamine—Beta—Hydroxylase Activity in Rat

After hypophysectomy, rat serum dopamine—beta—hydroxylase (DBH) activity rose continuously and doubled within 5 weeks. The increase in DBH levels was not reversed by replacement doses of ACTH. Vasopressin reduced the increased levels of serum DBH activity in hypophysectomized rats to those found in sham—operated control animals, but had no effect on serum enzyme activity in sham—operated controls. Three days after the last vasopressin injection, serum DBH activity in hypophysectomized animals again reached pretreatment levels. Intravascular volume seems to be a major factor in controlling serum DBH activity. It appears that the reduced intravascular volume and subsequent sympathetic neuronal hyperactivity resulting from the diabetes insipidus induced by hypophysectomy accounts for the elevated levels of serum DBH. (Endocrinology92: 1543, 1973)