Tissue-specific control of rat malic enzyme activity and messenger RNA levels by a high carbohydrate diet

B. Dozin, J. E. Rall, V. M. Nikodem

Research output: Contribution to journalArticle

45 Citations (Scopus)

Abstract

In euthyroid rats fed a high carbohydrate fat-free diet for 10 days, the mass of cellular malic enzyme mRNA in liver is increased 7-to 8-fold above the basal level. Malic enzyme activity is stimulated to the same extent. This effect does not result from an increase either in the transcriptional activity of the malic enzyme gene, as determined by nuclear run-off transcription assay, or in the content of intranuclear malic enzyme RNA sequences. Mathematical modeling shows that this increase in cytoplasmic mRNA is compatible with retarded degradation of cytoplasmic mRNA. Regulation of malic enzyme by carbohydrates is liver-specific, since no response is observed in the following nonhepatic tissues: brain, heart, spleen, kidney, testis, and lung. Furthermore, the amplitude of the response in liver depends on the thyroid state of the animals, being lower (by a factor of ≃4) in hypothyroidism and higher (12- to 15-fold) when normal animals are injected simultaneously with a daily dose of 15 μg of triiodothyronine per 100 g of body weight for 10 days. Since thyroid hormones regulate liver malic enzyme synthesis predominantly at the nuclear level and carbohydrates at the cytoplasmic level, the additive effect of triiodothyronine and a high carbohydrate diet on the activity of malic enzyme is readily explicable.

Original languageEnglish
Pages (from-to)4705-4709
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume83
Issue number13
Publication statusPublished - 1986

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Carbohydrates
Diet
Messenger RNA
Enzymes
Liver
Triiodothyronine
Fat-Restricted Diet
RNA Stability
Hypothyroidism
Thyroid Hormones
Testis
Thyroid Gland
Spleen
Body Weight
Kidney
Lung
Brain
Genes

ASJC Scopus subject areas

  • General
  • Genetics

Cite this

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abstract = "In euthyroid rats fed a high carbohydrate fat-free diet for 10 days, the mass of cellular malic enzyme mRNA in liver is increased 7-to 8-fold above the basal level. Malic enzyme activity is stimulated to the same extent. This effect does not result from an increase either in the transcriptional activity of the malic enzyme gene, as determined by nuclear run-off transcription assay, or in the content of intranuclear malic enzyme RNA sequences. Mathematical modeling shows that this increase in cytoplasmic mRNA is compatible with retarded degradation of cytoplasmic mRNA. Regulation of malic enzyme by carbohydrates is liver-specific, since no response is observed in the following nonhepatic tissues: brain, heart, spleen, kidney, testis, and lung. Furthermore, the amplitude of the response in liver depends on the thyroid state of the animals, being lower (by a factor of ≃4) in hypothyroidism and higher (12- to 15-fold) when normal animals are injected simultaneously with a daily dose of 15 μg of triiodothyronine per 100 g of body weight for 10 days. Since thyroid hormones regulate liver malic enzyme synthesis predominantly at the nuclear level and carbohydrates at the cytoplasmic level, the additive effect of triiodothyronine and a high carbohydrate diet on the activity of malic enzyme is readily explicable.",
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N2 - In euthyroid rats fed a high carbohydrate fat-free diet for 10 days, the mass of cellular malic enzyme mRNA in liver is increased 7-to 8-fold above the basal level. Malic enzyme activity is stimulated to the same extent. This effect does not result from an increase either in the transcriptional activity of the malic enzyme gene, as determined by nuclear run-off transcription assay, or in the content of intranuclear malic enzyme RNA sequences. Mathematical modeling shows that this increase in cytoplasmic mRNA is compatible with retarded degradation of cytoplasmic mRNA. Regulation of malic enzyme by carbohydrates is liver-specific, since no response is observed in the following nonhepatic tissues: brain, heart, spleen, kidney, testis, and lung. Furthermore, the amplitude of the response in liver depends on the thyroid state of the animals, being lower (by a factor of ≃4) in hypothyroidism and higher (12- to 15-fold) when normal animals are injected simultaneously with a daily dose of 15 μg of triiodothyronine per 100 g of body weight for 10 days. Since thyroid hormones regulate liver malic enzyme synthesis predominantly at the nuclear level and carbohydrates at the cytoplasmic level, the additive effect of triiodothyronine and a high carbohydrate diet on the activity of malic enzyme is readily explicable.

AB - In euthyroid rats fed a high carbohydrate fat-free diet for 10 days, the mass of cellular malic enzyme mRNA in liver is increased 7-to 8-fold above the basal level. Malic enzyme activity is stimulated to the same extent. This effect does not result from an increase either in the transcriptional activity of the malic enzyme gene, as determined by nuclear run-off transcription assay, or in the content of intranuclear malic enzyme RNA sequences. Mathematical modeling shows that this increase in cytoplasmic mRNA is compatible with retarded degradation of cytoplasmic mRNA. Regulation of malic enzyme by carbohydrates is liver-specific, since no response is observed in the following nonhepatic tissues: brain, heart, spleen, kidney, testis, and lung. Furthermore, the amplitude of the response in liver depends on the thyroid state of the animals, being lower (by a factor of ≃4) in hypothyroidism and higher (12- to 15-fold) when normal animals are injected simultaneously with a daily dose of 15 μg of triiodothyronine per 100 g of body weight for 10 days. Since thyroid hormones regulate liver malic enzyme synthesis predominantly at the nuclear level and carbohydrates at the cytoplasmic level, the additive effect of triiodothyronine and a high carbohydrate diet on the activity of malic enzyme is readily explicable.

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