Influence of Pyridoxine on Tyrosine Transaminase Activity in Maternal and Fetal Rat Liver

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Abstract
Massive doses of pyridoxine (100 mg/100 g body weight) were administered to nonpregnant and pregnant intact and adrenalectomized rats to determine whether alterations in tyrosine transaminase activity (TTA) and holotyrosine transaminase activity (HTA) could be produced and whether the responses differed in pregnant and nonpregnant states. Observations were made 5 hours after intraperitoneal injections of saline, cortisol or pyridoxine. Hepatic HTA tended to be higher and TTA was higher in saline-treated pregnant than in nonpregnant animals. Similar enzyme responses were observed in cortisol-treated animals compared with saline treated controls. Pyridoxine administration caused apparent stimulation of TTA and HTA in intact animals, but no increases in the enzyme activities were observed in similarly treated adrenalectomized rats. Similarities between the enzyme responses observed following pyridoxine administration and those following tyrosine administration are discussed in relation to age dependency. Increased TTA and HTA were observed only in fetuses from rats treated with pyridoxine, suggesting that the mechanism of stimulation of the enzyme by pyridoxine may be operative in fetal liver.