Biomedical subjects
Publications and source records attributed to M Benedix.
The malic enzyme activities of selected organs of rats have been investigated in dependence on age. The liver of female adult animals shows maximum enzyme level, while the malic enzyme activity of heart, kidney, brain, skeletal muscle, adipose tissue and lung is decreased in the given order. Excepting brain, for all tissues under study an age-dependent reduction of malic enzyme is observed.
The existence of a so-called "vitauct process" is discussed by means of the glucocorticoid-induced stimulation of tyrosine aminotransferase activity. Own experiments show that the highest possible stimulation of the enzyme by cortisol and stress in the liver of old Wistar rats is not lower than in young-adult animals. After stress and 4 h after cortisol injection of 0.75 mg/100 g b.w. even a higher sensitivity seems to exist. A main problem for the interpretation of the results is the treatment of the control animals. Stress-free animals and animals to which the hormone-free solvent only under light ether narcosis was injected i.p. (stressed controls) were used. With the lowest injected hormone dose (0.25 mg cortisol/100 g b.w.) the results lie below those of the stressed controls. As a result of the findings of this paper, of the role of the enzyme, and of different influencing factors (e.g., glucocorticoid receptors) we suggest that the used model does not allow a conclusive decision about the existence of a vitauct process.
In male Wistar rats the influences of age and experimental obesity on the activity of malic enzyme (EC 1.1.1.40) in different organs were studied. Obesity was induced in newborn rats by injection of Na(+)-L-glutamate (2 mg/g b.w. daily) subcutaneously in the first 5 days. The enzyme activity was measured at the ages of 2, 6 and 18 months. In control animals the highest enzyme activities were found in the heart muscle, liver, epididymal fat pad and skeletal muscle after 6 months. After 18 months the activities in these organs are considerably reduced. In the kidneys the activity between the 2nd and the 18th months tends to decrease continuously and only the brain shows an opposite trend. In comparison with the control animals, in glutamate treated rats the enzyme activity doubles nearly in the lipogenic organs liver and fat tissue in all age groups. In liver and fat tissue of 6-month-old rats, previously treated with clonidine to stimulate growth hormone secretion, the activities are lower than in glutamate obese rats without clonidine, but still higher than in normal control animals. The qualification of glutamate obese rats as a model for the study of age-associated diseases like obesity or diabetes mellitus type II needs further investigation.