Stage of Development and Fasting Affect Protein Synthetic Activity in the Gastrointestinal Tissues of Suckling Rats

Abstract

We studied suckling rats from 1 to 28 d of age to determine the normal developmental changes in the protein synthetic activity of gastrointestinal tissue. We also studied the changes that occurred in response to 10 or 18 h of fasting at 5, 10, 16 and 28 d of age. Protein synthesis was measured in vivo using a flooding dose of L-[4-3H]phenylalanine. Fractional protein synthesis rates (FSR, %/d) of stomach and small intestines increased nearly 80% during the period normally associated with weaning (d 18 to 28). Between birth and 28 d, the pancreas FSR increased approximately 6.5-fold from 46 to 302%/d. The increases in stomach, small intestinal and pancreatic FSR were largely due to increases in translational efficiency (gram protein synthesized per gram RNA). At 5, 10, 16 and 28 d postpartum, both the FSR and translational efficiency in pancreatic and small intestinal tissues were decreased after 10 h of fasting; however, measures in stomach tissue were largely unaffected. The magnitude of decline in FSR and translational efficiency in response to fasting was greater during the earlier than in the later stages of development. The results suggest that the FSR in the pancreas, small intestines and stomach of suckling rats increase during the period of development associated with weaning. Fasting affected protein synthetic activity more profoundly in pancreatic and small intestinal tissue in the early stages of development.

Nutrient-Independent and Nutrient-Dependent Factors Stimulate Protein Synthesis in Colostrum-Fed Newborn Pigs

“…The tissue samples were homogenized in 0.2 mollL PCA as described previously (19). The PCA-soluble homogenate supernatants containing the tissue free amino acid pools were separated from the PCA-insoluble precipitates and neutralized.…”

Steady State Is Not Achieved for Most Plasma Amino Acids during 12 Hours of Fasting in the Neonatal Piglet

“…During a fast, the pool size of almost all amino acids declines rapidly in the acute phase because dietary inputs to the pools have been removed. Beyond this initial decline, net protein synthesis decreases (15)(16)(17). Thus, the contribution to the pool of free amino acids from protein catabolism increases relative to the removal of the amino acids for protein synthesis.…”

Repression of Fat-Dependent Intestinal Apo A-IV mRNA Abundance by Medium Chain Triacylglycerols and Proteins, and Elevation by Carbohydrates of Fat-Dependent Apo A-IV Transport in Suckling Rat Pups.

“…A high plasma insulin/glucagon ratio was seen to increase apo A-IV mRNA abundance (7) and its translation (32) in rat hepatocytes. The concentra tion of plasma insulin, which is known to decrease ketogenesis in suckling rats and starved rats (22), has been reported to be lower in overnight fasted rat pups than in fed pups (33), and a high dose of glucose enhances insulin secretion (34). Consequently, the high insulin/glucagon ratio may also favor the flow of fatty acid into the esterification pathway rather than into the oxidation pathway in the intestine of the developing rat.…”