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Circadian Variation of Liver Metabolites and Amino Acids in Rats Adapted to a High Protein, Carbohydrate-Free Diet¹

James L. Robinson^*, Sana Foustock, Marc Chanez, Brigitte Bois-Joyeux and Jean Peret²

^* Department of Dairy Science, University of Illinois, Urbana, IL 61801 Centre de Recherches sur la Nutrition du C.N.R.S., 9 rue Jules Hetzel, 92190 Meudon-Bellevue, France

Diurnal variation in hepatic levels of lactate, pyruvate, phosphoenolpyruvate (PEP), -ketoglutarate, malate, oxaloacetate, ketone bodies, alanine, serine, glycine, aspartate, glutamate, glutamine, valine, urea, adenine nucleotides and inorganic phosphate were studied in rats adapted to a high protein, carbohydrate-free diet for 24 days. Most circadian rhythms differed in relation to controls (10% protein diet); many merely had different amplitudes, some were inverted, and some exhibited drastically altered patterns. Cytoplasmic redox state exhibited nearly similar variations and phosphorylation state differed primarily in amplitude whereas mitochondrial redox state was highly depressed in the absorptive phase. The metabolic regulation implied by the results is discussed in relation to both circadian variations of plasma insulin and glucagon concentrations, and pyruvate kinase and phosphoenolpyruvate carboxykinase activities previously reported.

KEY WORDS: • protein • circadian rhythms • liver metabolites

¹ Represents part of a doctoral thesis submitted by S. Foustock to the University of Paris VI.

² To whom reprint requests should be sent (France).

Manuscript received 20 February 1981.