Cortisol-induced increase of tyrosine-α-ketoglutarate transaminase in the isolated perfused rat liver and its relation to ribonucleic acid synthesis

Ottavio Barnabei , Fabio Sereni
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引用次数: 52

Abstract

It was shown that cortisol increases the level of tyrosine-α-ketoglutarate transaminase (l-tyrosine: 2-oxoglutarate aminotransferase, EC 2.6.1.5) of the isolated rat liver, when perfused with diluted rat blood containing an amino acid mixture; a more striking increase was obtained in the presence of a supplementary amount of tyrosine. This enhancement of activity was blocked by inhibitors both of protein synthesis (chloramphenicol, puromycin, ethionine) and of ribonucleic acid synthesis (actinomycin D and mitomycin C).

Adding [6-14C]orotate to the perfusing blood, caused a rapid incorporation of radioactivity into nuclear ribonucleic acid to take place; cytoplasmic ribonucleic acid was poorly labelled after 30 min, but its radioactivity rose thereafter. Cortisol stimulated the labelling of both the nuclear and the cytoplasmic ribonucleic acid; moreover it induced the increase of tyrosine transaminase after a lag of about 30 min. In both cases, the effect of the hormone was prevented by actinomycin D, or by mitomycin C.

It was finally found that livers perfused with cortisol have a higher nuclear ribonucleic acid polymerase (nucleosidetriphosphate: RNA nucleotidyltransferase, EC 2.7.7.6) activity than control ones.

The facts that the synthesis of nuclear ribonucleic acids precedes the increase of tyrosine transaminase and also that cortisol stimulates ribonucleic acid polymerase strongly suggest that the action of the hormone can be related to an increase in the synthesis of messenger ribonucleic acid molecules for the synthesis of the enzyme.

皮质醇诱导离体灌注大鼠肝脏酪氨酸-α-酮戊二酸转氨酶升高及其与核糖核酸合成的关系
结果表明,当用含有氨基酸混合物的稀释大鼠血液灌注时,皮质醇增加了离体大鼠肝脏中酪氨酸-α-酮戊二酸转氨酶(l-酪氨酸:2-氧戊二酸转氨酶,EC 2.6.1.5)的水平;在补充一定量的酪氨酸的情况下,获得了更显著的增加。这种增强的活性被蛋白质合成抑制剂(氯霉素、嘌呤霉素、乙硫氨酸)和核糖核酸合成抑制剂(放线菌素D和丝裂霉素C)所阻断。向灌注的血液中加入[6-14C]旋酸酯,导致放射性物质迅速掺入核糖核酸;30min后细胞质核糖核酸标记不清,但此后其放射性上升。皮质醇刺激细胞核和细胞质核糖核酸的标记;在这两种情况下,放线菌素D或丝裂霉素c都能阻止激素的作用。最后发现,灌注皮质醇的肝脏比对照组有更高的核糖核酸聚合酶(核苷三磷酸:RNA核苷酸转移酶,EC 2.7.7.6)活性。核核糖核酸的合成先于酪氨酸转氨酶的增加,以及皮质醇刺激核糖核酸聚合酶的事实强烈表明,激素的作用可能与合成酶的信使核糖核酸分子合成的增加有关。
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