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

Abstract

Summary. The aim of the present work was to determine whether the increase in monoamine oxidase activity previously found in hyper-and 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 hyper-and 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.The results show that thyroxin controls monoamine oxidase activity in the newborn rat primarily by acting on the rate of synthesis of the enzyme.Introduction.

Tyrosine Hydroxylase Activity and Catecholamine Content in the Adrenals of Young Hypo- and Hyperthyroid Rats

“…In this respect, it appeared interesting to study their effects in few steps involved in catecholamine physiology of the developing rat. In previous papers, we described the influence of the thyroid status on the development of monoamine oxidase (4,5) and catechol-omethyltransferase (6) activities in different organs of the young rat.…”

Influence of Hypo- and Hyperthyroidism on Noradrenaline Metabolism in Brown Adipose Tissue of the Developing Rat

“…During the same period, hypothyroidism induces an increase in the activities of both MAO and COMT, while hyperthyroidism has the opposite effect on MAO. We have already shown that the increase in MAO activity following hypothyroidism in BAT of the young rat is the consequence of an increased synthesis rate of the enzyme (9).…”