Circadian rhythm of protein synthesis activity in the exocrine pancreas of fed and starved rats.

Rats, either fed a solid standard chow ad libitum or starved for 24 h prior to the beginning of the experiments, were kept in a normal light-dark cycle of 12 h. At certain times over a total period of 24 h, three animals of each group were killed, their pancreata were excised and the protein synthetic capacity was determined, measuring both the amount of cellular RNA and the percentage of ribosomes active in protein synthesis. A clear-cut circadian rhythm in the synthetic activity was found, well expressed in the fed animals but less evident and shifted in time in the starved ones. The RNA/DNA ratios in the two sets of animals remained fairly constant throughout the day, but were somewhat lower in the fasted rats.