The permissive role of cortisol in the regulation of rat liver tyrosine aminotransferase

Abstract

MAVWW, C., ~m LANE, E. A. The permissive rok of cortisol in the regulation of rat liver tyrosine aminotransferase. Can. J. Biochem. 48, 13-19 (1970).The daiIy rhythm in the activity of rat liver tyrosine aminotransferase was abolished after 3 weeks of constant illumination. The rhythm reappeared only partially in rats bilaterally adrenalectomized immediately after the 3-week period and returned to a cyclic lighting schedule. The failure of the enzyme rhythm to reappear fully did not seem to originate in dietary factors since food consumption and rate of growth were similar in the adrenalectomized and sham-operated control rats. Developmental studies showed that the adult rhythm was absent in rats up to 15 days old but present in 21-day-old rats. Although the rhythm appears to be generated in part by the rhythmic intake of dietary amino acids, a role for the endogenous glucocorticoids was suggested by the finding that physiological amounts of cortisol played a permissive role in the stimulation of enzyme activity by amino acids (casein hydrolysate) in adrenaIectomized rats. These amounts of cortisol greatly stimulated enzyme activity in rats fed a protein-free diet. A regulatory role for glucocorticoids based on this permissive action is envisaged in the daily rhythm of tyrosine aminotransferase.

Effect of environmental stress of low pressure on tyrosine aminotransferase and phenylalanine 4-hydroxylase activities in the rat

“…Excluding protein synthesis, the major pathway for the metabolism of tyrosine involves tyrosine aminotransferase (EC 2.6.1.5.). In view of the altered metabolism of noradrenaline and corticosteroids, both of which are known to control the activity oi tyrosine aminotransferase (Black & Axelrod, 1970;Mavrides & Lane, 1960), a study of the activity of this enzyme under conditions of low pressure seems Vol. 150 worth while.…”