GTP, in physiologic concentration, enhances the binding of cAMP to a protein in the hepatic cytosol that may be the regulatory subunit of protein kinase II. Ingestion of carbohydrate suppresses hepatic gluconeogenesis and glycogenolysis, two processes that are stimulated by cAMP. In this study, we have examined the possibility that carbohydrate inhibits these processes partly by decreasing the sensitivity of the GTP-responsive cAMP-binding protein to the effect of GTP. We found that 100 μM GTP was much less effective in enhancing cAMP binding in the hepatic cytosol of rats given 15% glucose for 2 days than in the cytosol of fasted rats [21 ± 3% (mean ± SE) increase vs. 67 ± 6%, P < .01]. Corresponding results were noted in diethylaminoethyl (DEAE)-cellulose extracts of the hepatic cytosol of these rats. GTP stimulation of cAMP binding was also diminished in the hepatic cytosol of diabetic rats treated for 7 days with insulin compared with that of untreated diabetic rats (29 ± 10 vs. 81 ± 11% increase, P < .01), but this could have been due to increased food intake in the treated rats. We conclude that GTP stimulation of hepatic cAMP binding is decreased in the carbohydrate-fed state and that this effect may be mediated by the increase in plasma insulin induced by carbohydrate. Our observations suggest that some of the cellular effects of cAMP may be regulated by modulation of the stimulatory effect of GTP on the GTP-responsive cAMP-binding protein.
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Original Contributions|
January 01 1987
Effects of Fasting, Feeding, and Insulin on Enhancing Effect of GTP on cAMP Binding in Rat Hepatic Cytosol Free
Edward M Rosenberg;
Edward M Rosenberg
Department of Medicine, Neil Hellman Research Building, Albany Medical College of Union University
Albany, New York
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A David Goodman;
A David Goodman
Department of Medicine, Neil Hellman Research Building, Albany Medical College of Union University
Albany, New York
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Thomas I Lipinski
Thomas I Lipinski
Department of Medicine, Neil Hellman Research Building, Albany Medical College of Union University
Albany, New York
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Address correspondence and reprint requests to Dr. Edward M. Rosenberg, Albany Medical College of Union University, 47 New Scotland Avenue, Albany, NY 12208
Diabetes 1987;36(1):37–42
Article history
Received:
March 18 1986
Revision Received:
June 13 1986
PubMed:
3025042
Citation
Edward M Rosenberg, A David Goodman, Thomas I Lipinski; Effects of Fasting, Feeding, and Insulin on Enhancing Effect of GTP on cAMP Binding in Rat Hepatic Cytosol. Diabetes 1 January 1987; 36 (1): 37–42. https://doi.org/10.2337/diab.36.1.37
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