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Influences of Age and Weaning on In Vivo Pancreatic Protein Synthesis in the Lamb¹

Laboratoire d'Etude du Métabolisme Azoté, INRA et CNRS U.A. 11 23, Theix, 63122 Ceyrat, France

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 > 0.05). This lack of developmental change resulted from constant (P > 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 > 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 < 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 < 0.005). Finally, there was a relationship between pancreatic protein synthesis and protein intake in only ruminant lambs.

KEY WORDS: • protein synthesis • RNA • development • weaning • pancreas • lamb

¹ This study was supported by a grant from the French Ministry of Research and Technology.

² To whom reprint request should be addressed.

³ Present address: Warsaw Agricultural University, Institute of Human Nutrition, ul. Nowoursynowska 166, 02-766, Warszawa, Poland. During this work, D. Rosolowska-Huszcz held a postdoctoral fellow-ship from the CIES and the INRA.

Manuscript received 28 June 1988. Revision accepted 31 October 1988.