The Inductions of Tyrosine Aminotransferase by Glucagon and Hydrocortisone

Variation of tyrosine aminotransferase expression during the day in rats of different ages

The activity of the enzyme tyrosine aminotransferase and the synthesis of its specific mRNA were evaluated at different hours of the day in the liver of 3-, 12- and 24-month old BN rats. The enzyme activity has a circadian rhythm with a peak at midnight in 3- and 12-month old, which shifts to 03.00 hrs in 24-month old animals, in agreement with previous results. The expression of TATmRNA also changes during the day indicating circadian fluctuations which change with age. In 3-month old rats the TATmRNA peak is at 19.00 hrs, preceding that of the enzyme activity. In 12-month old rats the TATmRNA synthesis reaches a maximum at midnight and in 24-month old rats at 03.00 hrs. The results show that the circadian rhythm of tyrosine aminotransferase activity is due to a different gene expression throughout the day, which is influenced by age.

Oxidative response to aldosterone of pyridine nucleotide in rat kidney in situ

In an attempt to elucidate early biochemical events in the action of aldosterone on rat kidney in situ, the response of the pyridine nucleotide oxidation-reduction state of surface cells was directly and continuously recorded with an organ-fluorometer. Intravenous administration of aldosterone induced a rapid (maximum response in 10 min) and dose-related (2.5-25 microng/100 g rat) oxidative response that was specific to aldosterone and to the kidney. The oxidative response was 1) detectable with minute dise (approximately 0.2 microng/100 g rat) of hormone: 2) reproduced by other mineralocorticoids; 3) enhanced by a maneuver for expanding the extracellular fluid compartment or by adrenalectomy; and 4) prevented by spironolactone, progesterone, actinomycin D, and cycloheximide. All of these data argue that the redox response is related to the subsequent changes in aldosteronemediated ion transport. Experiments with an uncoupler and with redox substrates showed that mitochondrial NADH was the major nucleotide pool responding to hormone. The oxidation was not accompanied by changes in the adenylate energy charge level of the whole organ. These observations support the view that aldosterone acts on energy metabolism of tubular cells before developing apparent cation transport effects.