EFFECT OF THYROID HORMONE ON METABOLISM OF PTEROYLGLUTAMIC ACID AND LIVER LEVELS OF NUCLEIC ACIDS AND NITROGEN

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Abstract
Liver levels of nucleic acids, nitrogen content, and metabolism of PGA were studied in thyroidectomized, hyperthyroid and control rats. For comparison, rats treated with either thiouracil or DNP were examined. Hyperthyroidism caused an increase both in liver nucleic acids and nitrogen, whereas thyroidectomy led to a lowered level of RNA only. Compared with thyroidectomized rats, livers of thiouracil-treated animals contained similar amounts of both nucleic acids and nitrogen per gm. liver, but significantly more per unit body weight, resulting from the enlargement of the liver. Administration of DNP reduced RNA concentration per gm. liver, did not alter the DNA level and increased the liver nitrogen content. Both storage of FA and CF, and the conversion of PGA to CF were normal in thyroidectomized rats. Thyroid treatment however led to an increase in liver FA and impairment of CF formation from PGA. But an even greater inhibition of CF formation was observed in rats treated with either thiouracil or DNP. DNP affects the storage capacity of the liver for FA and CF. Our experiments would indicate that both RNA and DNA concentrations of rats'' liver are rather independent of PGA metabolism. These results are consistent with the view of the existence of an alternative pathway for nucleic acid synthesis in the rat liver, which is independent of either FA or CF.