Schedule of Protein Ingestion and Circadian Rhythm of Certain Hepatic Enzyme Activities Involved in Glucose Metabolism in the Rat

Abstract

The circadian rhythms of liver glycogen, plasma glucose, corticosterone and insulin, and hepatic activity of PK, G6PDH, ME, Ac.CoA carbox. PEP-CK and GPT were studied in adult rats. Animals either received a mixed diet ad libitum (8 % protein) or a protein meal (1.1 g protein) given at 05:00 or 17:00 h, with free access to a protein-free diet (separately fed). When the protein meal was ingested during the lighted period (17:00) the 24-hour average level of liver PEP-CK was greater than in rats consuming protein during darkness (05:00). In the latter case, modification of the circadian rhythm of liver glycogen and of circadian rhythm of liver PK, G6PDH, ME and Ac.CoA carbox. activity (increase of 24 h average level, extension of period of high activity, sudden increase after ingestion of protein meal) were observed. Conversely, the circadian rhythm of plasma insulin and corticosterone and of liver PEP-CK and GPT activity were only slightly affected by the mode of feeding.

Sirtuins and Pyridine Nucleotides

“…It has indeed been shown that the pancreas is dependent on eNampt and extracellular NMN for glucose-induced insulin secretion, which may partly explain why dysregulation of the circadian cycle affects glucose metabolism 32 . Indeed, metabolism 47–49 , as well as aging 50, 51 , are known to be under the influence of the circadian rhythm, which further supports their connection to NAD + world and sirtuins. The brain, which centrally regulates metabolism via Sirt1, is also deficient in iNampt, however, there is no direct evidence yet of how essential circulating NMN is for it function.…”

Circadian regulation of metabolism

“…Interestingly, time-of-day-dependent rhythms in glycogen levels persist in fasted rodents (albeit at lower amplitude), suggesting that these rhythms are not simply secondary to feeding/fasting cycles (Ishikawa and Shimazu 1976). Not only do glycogen levels oscillate over the course of the day, but so do the activities of key glycogen metabolism enzymes; glycogen synthase displays maximum levels during the dark (active) phase in rodents, whereas glycogen phosphorylase peaks towards the end of the light (sleep) phase (Ishikawa and Shimazu 1980; Peret, et al 1976). Evidence in support of circadian clock involvement in mediation of these oscillations comes from recent studies by Doi et al, which report diminished oscillations in both hepatic glycogen levels and glycogen synthase expression/activity in Clock Δ19 mutant mice (Doi, et al 2010).…”

Periodicity in Protein Metabolism: Time Patterns of Substrate Interaction and Utilization

“…In contrast, there is increased activity of insulin and insulin-sensitive enzymes if the protein is consumed at the end of the night. 119,120 The above data suggest that protein turnover is a function both of the time of protein ingestion and of the other nonprotein components. While this has been demonstrated in liver, there is lack of data on the metabolic interrelationships of protein, amino acids, and dietary factors in muscle.…”