Schedule of protein ingestion and circadian rhythm of certain hepatic enzyme activities involved in glucose metabolism in the rat.

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.