Effects of Fasting and Feeding on Protein Synthesis by the Rat Pancreas

Abstract

A B S T R A C T These experiments were designed to determine whether fasting and feeding were associated with differing rates of protein synthesis in the rat pancreas. It has been established that feeding, acetylcholine, or cholecystokinin-pancreozymin administration was associated with enhanced rates of digestive enzyme secretion; however, the literature is unclear as to effects of such stimulation on enzyme synthesis. Rats fed ad lib. or fasted 24, 48, or 72 hr were used for this study. Pancreases were removed and incubated in tissue culture medium with L-phenylalanine-"C, and incorporation into TCA-insoluble material as well as purified amylase was measured. Compared with fed controls, fasting 24, 48, and 72 hr was associated with 29%, 39%, and 35% decreases in incorporation of L-phenylalanine-14C into protein. Decreases of similar magnitudes were apparent whether the data were expressed in terms of protein or DNA. Pancreatic amylase isolated from rats fasted 48 hr contained 57% fewer counts of L-phenylalanine-'C than amylase isolated from fed rats. Moreover, rats fasted for 24 hr and given bethanechol chloride incorporated greater amounts of L-phenylalanine-1C into protein than fasted controls. Studies were performed to exclude changes in pool size of precursor (L-phenylalanine-"C) or product (amylase) in accounting for decreases associated with fasting. These studies demonstrate that fasting was associated with decreased rates of pancreatic amylase and protein synthesis in rats.

DNA and Protein Synthesis in Developing Rat Pancreas

“…Morisset and Webster (23) found that incorporation of [I4C]-phenylalanine at a concentration of 48 pM into protein was linear for at least 120 min in adult pancreas and the rate of incorporation was not dependent on phenylalanine pool size. In contrast Bauduin et al (24,25) found that while incorporation of L-[4,5-3H]-leucine in vitro into rat pancreas was linear for less than 20 min at a concentration of 26 p M leucine, it was linear for 2 h at a concentration of 0.8 mM.…”

Variations nycthémérales des protéases pancréatiques chez le poulet nourri par repas

“…phénomène discontinu fortement stimulé par l'ingestion d'aliments. Morisset et al [1972] ont clairement montré à partir de cultures de tissu pancréatique de rats que la synthèse est également un processus variable et qu'une augmentation de la sécrétion est fréquem ment associée à une augmentation de la syn thèse. L'existence d'une intense stimulation de la synthèse pancréatique en période post prandiale est confirmée par Girard-Globa [1980].…”

Protein Synthesis in Pancreas of Fasted Pigeons

“…In addition, rates of incorporation of [ 3 H]uridine into RNA were lower in pancreatic tissue slices prepared from fasted compared with fed birds (15) . Preliminary experiments (9) suggested that particulate factors concerned with protein synthesis (in vitro) were more affected by fasting than were soluble factors . In the experiments reported here, there were decreases in amounts of polysomal RNA as well as a shift to monosomes and disomes .…”

“…(17) was used as reported previously (9) . (21), and either 5 mg ER, 4 mg polysomes, or 2 mg salt-washed ribosomes .…”

“…On the other hand, Stenram and Hirschman, by means of autoradiography (7), observed increased protein labeling suggesting enhanced synthesis . Recently we have shown (8,9) that slices of pancreas from fasting rats undergo not only a loss in total protein and RNA content but a loss in protein synthesizing capability. Further, we have shown (9,10) THE JOURNAL OF CELL BIOLOGY • VOLUME 57, 1973 • pages [1][2][3][4][5][6][7][8] that in rats and pigeons fasting results in a lower incorporation of amino acids into protein and that this appeared to involve changes in both the microsomal and supernatant elements .…”