Studies on the nature of the increased monoamine oxidase activity in the rat heart after adrenalectomy

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Abstract
The increased activity, induced by adrenalectomy, of the enzyme monoamine oxidase (MAO) in the rat heart was found to resemble closely that present in the hearts of control animals. No significant differences were observed in the nature of the response to heat denaturation, changes in pH or to inhibition by pargyline or clorgyline. The relative activities using the substrates tyramine, 5-hydroxytryptamine, dopamine or benzylamine were the same. No evidence was found to suggest the presence of a heat-stable or dialysable inhibitor of enzyme activity. In young rats there was an increase in the relative enzyme activity using benzylamine as substrate, compared with the activity using tyramine, in the first few days after adrenalectomy. No effect of adrenalectomy could be detected upon the MAO activity in the rat brain or liver. It is concluded that the increase in rat heart MAO following adrenalectomy cannot be due to the synthesis of an enzyme with different catalytic properties, nor to the transformation of the existing enzyme into one of increased catalytic ability but with different properties.