Influences of age and weaning on in vivo pancreatic protein synthesis in the lamb.

ABSTRACT

In vivo pancreatic protein synthesis rates were obtained from the uptake of L-[3,4(n)-3H]valine co-injected with a flooding dose of unlabeled valine into 1-, 5-, and 8-wk-old suckling lambs, and 8-wk-old weaned animals. Protein fractional synthesis rate was 184%/d at 1 wk of age and 153%/d in 5-wk-old animals (P greater than 0.05). This lack of developmental change resulted from constant (P greater than 0.05) ribosomal capacities (total RNA/protein ratios) and efficiencies of protein synthesis (synthetic rates relative to RNA). No further alteration for protein fractional synthesis rate (144%/d) occurred in 8-wk-old suckling animals (P greater than 0.05). In contrast, 8-wk-old ruminants exhibited higher protein fractional synthesis rate (244%/d) than 8-wk-old suckling animals, although ribosomal capacity was markedly higher in both 8-wk-old groups than in youngest animals (P less than 0.05). The present findings clearly indicate that in vivo protein synthesis in the developing ovine pancreas depends primarily on age. Potentialities for increased rates of pancreatic protein synthesis, i.e., increases in total RNA content and ribosomal capacity appear between 5 and 8 wk of age in this species. At 8 wk of age, however, when lambs are generally weaned, solid food ingestion resulted in a rise for both fractional and absolute rates of protein synthesis, essentially because ruminants maintained a higher efficiency of protein synthesis than milk-fed animals (P less than 0.005). Finally, there was a relationship between pancreatic protein synthesis and protein intake in only ruminant lambs.