Specific changes in type A and B monoamine oxidase activity in different tissues of hypophysectomized rats

MAO activity was tested in four organs of young male rats 16 days after hypophysectomy. Five monoamines were used as substrates. In the adrenal glands and the thyroid gland MAO activity towards the substrates preferably deaminated by MAO-A was severely decreased. In the adrenal glands, but not in the thyroid gland, the effect of hypophysectomy could be simulated with dexamethasone, a steroid which inhibits ACTH secretion. A significant rise in MAO activity towards substrates for MAO-A and MAO-B occurred in the heart of hypophysectomized rats. There was little change in the MAO activity of whole brain homogenates after hypophysectomy.