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Plasma Glucagon and Insulin Concentrations and Hepatic Phosphoenolpyruvate Carboxykinase and Pyruvate Kinase Activities during and upon Adaptation of Rats to a High Protein Diet¹

Jean Peret^2,*, Sana Foustock^*, Marc Chanez^*, Brigitte Bois-Joyeux^* and Roger Assan

^* Centre de Recherches sur la Nutrition du C.N.R.S., 9 rue Jules Hetzel, 92190 Meudon-Bellevue, France Service de Diabétologie, Hôpital Bichat, 48 rue Huchard, 75018 Paris, France

Plasma hormones, glucose and free fatty acids, liver glycogen and two key enzymes of glycolysis and gluconeogenesis were examined in adult rats during a 40-day period of high protein feeding. Plasma insulin fell within 1 day but returned to normal after 4 days. Glucagon changed more slowly, reaching a maximum on day 4 and declined to near the control value within 24 days. Consequently, the insulin to glucagon ratio was lower on days 1, 4 and 8 and was nearly normal on day 24. With respect to hepatic enzymes, phosphoenolpyruvate carboxykinase activity rose sharply on the 1st day and remained elevated for 40-day period; the L-isozyme of pyruvate kinase, although unchanged on the 1st day, decreased thereafter and from day 8 on represented 15–20% of control. Circadian variations in these parameters were also measured in rats adapted to the high protein diet. In such animals, the diurnal change in plasma hormones was less marked but tended to be inverted with respect to controls; the insulin/glucagon ratio was highest during daylight on high protein and in late night on the control diet. Over 24 hours, pyruvate kinase activity was related directly and phosphoenolpyruvate carboxykinase inversely to the hormone ratio. We concluded that in rats adapted to high protein, as in controls, the diurnal balance between glycolysis and gluconeogenesis is probably regulated by the same factor, namely the insulin/glucagon ratio.

KEY WORDS: • protein • glucose • fatty acids • glycogen • insulin • glucagon • phosphoenolpyruvate carboxykinase • pyruvate kinase • circadian variations

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

² To whom reprint requests should be sent: Centre de Recherches sur la Nutrition du C.N.R.S., 9 rue Jules Hetzel, 92190 Meudon-Bellevue, France.

Manuscript received 29 September 1980.

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