THE EFFECT OF AGE AND THYROID HORMONES ON THE MONOAMINE OXIDASE OF RAT HEART

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Abstract
The activity of monoamine oxidase was studied in the heart mitochondria of normal and hyperthyroid rats using manometric techniques. A definite age effect was observed in normal rats with an increase from 0-trace activity in post-natal to approximately 1000 μl. O2 consumed/gram/hour in 5–600 gram rats. Desiccated thyroid diet (2%) and l-triiodothyronine produced an increase in heart monoamine oxidase activity of from 70 to 200% depending upon the age group of the animals used. d-Triiodothyronine did not have this stimulating effect when used at equimolar doses. The effect of oxygen tension on the oxidation rate of tyramine is different for the heart and liver enzymes.