HORMONAL ACTION ON MONOAMINE OXIDASE ACTIVITY IN RATS

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Abstract
Male young and adult rats were injected with thyroxin, hydrocortisone and puromycln. Monoamine oxidase (MAO) activity was studied in liver, brain, kidney, and heart with L-tryptamine-2-14C as substrate. After thyroxin treatment, heart MAO increased in young animals but decreased in adult animals. Thyroxin decreased liver MAO in adult animals. Brain MAO remained constant in all experiments, whereas kidney MAO showed a slight decrease after thyroxin injection. In young rats, puromycin did not prevent the increase in heart MAO caused by thyroxin injection. Hydrocortisone did not enhance MAO activity in liver, brain and heart. Of all organs studied, only the heart showed a marked increase of MAO with age. In female rats, thyroxin has little effect on brain and liver MAO, whereas it increases MAO activity in the heart of young and adult animals by 67% and 32% respectively. Adult female rats have twice as much heart MAO as males.