Regulation of Protein Synthesis and Enzyme Accumulation in the Rat Pancreas by Amount and Timing of Dietary Protein

Abstract

A 24-hour study in rats evidenced a clear rhythmicity of both synthesis and storage of pancreatic hydrolases. Synthesis measured by incorporation of 3H leucine into proteins was maximal during the night, reaching 21.3 mg/g tissue at 2400 hours against 4.1 mg/g at 0900 hours. Amylase and chymotrypsinogen contents, on the contrary, were 2-fold higher during the day (resting period) than at night (feeding period), while trypsinogen did not vary significantly. The diametrical opposition between the variations in synthesis and enzyme contents shows that, during periods of active feeding, stimulated synthesis merely balances excretion, while during periods of spontaneous fasting, basal synthesis is greater than basal secretion resulting in a preprandial accumulation of hydrolases. The effect of dietary proteins was investigated by feeding them as a separate meal at different times of the day while providing a protein-free diet ad libitum. In this case the general pattern of synthesis was biphasic. Rates of protein synthesis increased rapidly 2- to 3-fold after the protein meal, while tissue amino acids concentrations dropped. This first peak was tentatively attributed to the action of digestive hormones released after protein ingestion. The second peak occurred 15-18 hours, later together with a rise in tissue amino-acids due to limited endogenous proteolysis. This suggests that digestive hormones and amino-acid supply act independently to stimulate the synthesis of hydrolases in the pancreas. The amount of enzyme stored depends on the timing of the protein meal with respect to the period of most intense feeding, i.e. on the timing of maximal synthesis with respect to maximal secretion.

The effect of feeding on the secretion of pepsin, trypsin and chymotrypsin in the Atlantic salmon,Salmo salar L

“…This agrees with observations on the rat (Girard-Globa et al 1980) and on the catfish starved for 2 months (Yoshinaka et al 198 la). Ba- ).…”

“…sal synthesis and secretion are known to occur in the pancreas of mammals (reviewed by Case 1978;Girard-Globa et al 1980). Starvation also caused a gradual reduction of trypsin and chymotrypsin activities in the intestinal digesta indicating that secretion is greatly reduced upon withdrawal of food.…”

Trypsin restoration time in the pyloric ceca of yellowtail Seriola quinqueradiata

“…Giard‐Globa et al 22 . examined pancreatic protein synthesis after feeding in rats and found that enzyme synthesis began within 30 min after feeding.…”

“…Giard-Globa et al 22 examined pancreatic protein synthesis after feeding in rats and found that enzyme synthesis began within 30 min after feeding. In the present study, the trypsin synthesis time was estimated by reverse transcription PCR (RT-PCR) techniques.…”

Mesure de la digestibilité des protéines par la méthode des différences porto-artérielles chez l’espèce porcine

“…Ainsi, une quantité non négligeable d'azote endogène est sécrétée dans la lumière intestinale et mélangée avec l'azote alimentaire au cours de la digestion. L'importance de cette sécrétion dépend en outre de la nature des constituants des repas, des niveaux énergétiques et azotés de la ration et du taux de cellulose [7,16,22,49]. L'étude de la digestion et de l'absorption spécifique d'une protéine donnée n'est donc pas aisée en raison de cette contribution d'azote endogène difficile à estimer [2,20,23,44].…”