Studies on the Induction of Tyrosine Transaminase by Large Dose Administration of Vitamin B6

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Intraperitoneal as well as oral administration of pyridoxine 50mg per 100g body weight to rats resulted in a 2 to 3-fold rise of hepatic tyrosine transaminase (L-tyrosine 2-oxoglutarate aminotransferase EC 2.6.1.5.), the maximal activity being attained 4 hours after administration. This rise was also observed by intraperitoneal injection of some other vitamins.Bilateral adrenalectomy curtailed the rise by pyridoxine or pyridoxal administration but still a 150% increase of the activity was observed 2 to 4 days after the operation, while injection of pyridoxamine and other vitamins had no effect on the adrenalectomized rats. The induction of tyrosine transaminase by vitamin B6 derivatives, which was confirmed by Kenney et al. due to an increased rate of its de novo synthesis, was no more seen 7 days after adrenalectomy. The inducibility was restored by the pretreatment of hydrocortisone 5mg per 100g body weight of rats 15 hours before the injection of pyridoxine.This phenomenon together with the fact that the day course of the induction by pyridoxine after adrenalectomy seems to reflect the serum content of corticosterone of adrenalectomized rats as reported by Fazekas, supports the conclusion that the induction of tyrosine transaminase by pyridoxine is a secondary change mediated by glucocorticoid.
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