[Enzyme adaptation and "vitauct" process]

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.