The effect of hydrocortisone on tyrosine-alpha-ketoglutarate transaminase and tryptophan pyrrolase activities in the isolated, perfused rat liver.

Administration of hydrocortisone or cortisone to rats has been shown to produce a marked increase in hepatic tryptophan pyrrolase (1, 2) and tyrosine-cY-ketoglutarate transaminase’ (4, 5) activities. Although present evidence suggests that the rise in tryptophan pyrrolase activity involves the synthesis of new protein (6) and the rise in tyrosine transaminase activity may not (7), the mechanism of action of hydrocortisone is unknown. The question of whether or not the increased enzyme activities are the result of a direct action of hydrocortisone on hepatic cells was investigated in the present study. Since attempts to demonstrate a direct action of hydrocortisone on tryptophan pyrrolase activity in homogenates (1) or slices (8) of rat liver have been unsuccessful, as were similar attempts with tyrosine transaminase, we turned to the artificially perfused, isolated rat liver (9, 10). Hydrocortisone produced a distinct increase in activity of both enzymes in this preparation. Barnabei and Sereni (11) also have recently reported that hydrocortisone induced an increase in tyrosine transaminase activity in the isolated, perfused rat liver.