Male young and adult rats were injected with thyroxin, hydrocortisone and puromycin. 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.

Labeled N-acetyl-L-aspartic acid was injected intraperitoneally and intracerebrally into mice. Its metabolism was studied at different time intervals after injection by collecting CO2 and by identifying the radioactive metabolites in urine. The localization of injected labeled N-acetyl-L-aspartic acid and of L-aspartic acid was studied by autoradiography. The results show that N-acetyl-L-aspartic acid does not cross the blood–brain barrier, is rapidly metabolized, and that some is excreted unchanged through the kidneys. It can be concluded that N-acetyl-L-aspartic acid is synthesized in the brain and is rapidly metabolized in the body.

The activities of aspartate transcarbamylase and of five enzymes involved in the urea cycle were determined in the liver of rats from the embryonic state to adulthood. Aspartate transcarbamylase activity is very high in the embryo and at birth. It remains high until the rat reaches a body weight of 50 g, after which there is a rapid decrease which levels off to a plateau at adulthood. The enzymatic activities of carbamyl phosphate synthetase, ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinase, and arginase are very low at the embryonic stage. The activity of these enzymes increases gradually with age until a plateau is reached, except for argininosuccinase which also increases in young animals but decreases in adult life. Of these enzymes, argininosuccinate synthetase always has the lowest activity and seems to be the limiting factor in the synthesis of urea. These results indicate that the biosynthesis of pyrimidines and urea vary inversely at different ages that correspond to different metabolic activities of the animals. Thus, an inverse relation is established between the two pathways from carbamyl phosphate, leading to protein biosynthesis (formation of RNA from orotic acid) and to protein catabolism (formation of urea).

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A study of transaminase enzymes in various tissues of different species was carried out. Rabbits were fed with a vitamin E deficient diet. Controls receiving vitamin E were maintained on the same diet. Animals were killed at intervals and the glutamic-aspartic transaminase (GOT) and the glutamic-alanine transaminase (GPT) levels were determined in the muscle, blood, and liver.Mice with hereditary muscular dystrophy and normal litter mates which served as controls were killed at different stages of the disease and GPT and GOT levels were also determined in the muscle, blood, and liver.Important variations between the two types of dystrophy were noticed. Variations in the levels of GPT and GOT were also significant in blood and liver of dystrophic rabbits.Exogenous glutamic acid was injected to vitamin E deprived rabbits. Body weight losses and the onset of the terminal stage of the disease were much postponed when compared to the vitamin E deprived rabbits which did not receive glutamic acid.A discussion of the possible role of glutamic acid in muscular dystrophy of vitamin E deprived rabbits is presented.