On the nature of monoamine oxidase control by thyroxin in the heart , brain and brown adipose tissue of the developing rat

The aim of the present work was to determine whether the increase in monoamine oxidase activity previously found in hyperand hypothyroid rats, was due to thyroxin effects on enzymatic activity or to variations in enzyme synthesis. The rate of synthesis of monoamine oxidase in young hyperand hypothyroid rats has been studied by measuring the recovery of enzymatic activity 7 days after irreversible inhibition by Pargyline. Hyperthyroidism was followed by an increase in the rate of synthesis of monoamine oxidase in the heart and a decrease in the brain. Hypothyroidism led to an increase in brown adipose tissue. Thyroxin increased cardiac monoamine oxidase activity in vitro in the late fetal period, but not in the newborn or the adult.