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Phenylalanine Flooding Dose Procedure Is Effective in Measuring Intestinal and Liver Protein Synthesis in Sheep^1,2,

Department of Animal and Poultry Science, University of Guelph, Guelph, ON N1G 2W1 Canada

We conducted two experiments to evaluate the flooding dose method for measuring intestinal and liver protein synthesis in sheep. Experiment 1 showed that large doses of phenylalanine did not cause marked metabolic disturbances. Experiment 2 examined the effectiveness of flooding with phenylalanine and the time dependency of the protein synthesis calculation. Rams were injected with 1.2 MBq L-[ring 2,6-³H]phenylalanine/kg body wt and slaughtered 20, 40 or 60 min later. Plasma specific radioactivity reached a plateau within 2.5 min and did not change significantly (P > 0.05) throughout the experiment. Tissue intracellular free pool specific radioactivity also remained constant from 20 to 60 min postinfusion. Flooding conditions were achieved in the intracellular free pool of intestinal tissues (specific radioactivity 70–96% of plasma specific radioactivity), although liver flooding was less successful (57–67%). Protein synthesis rates measured after 20 min were significantly (P < 0.05) higher in the liver, jejunum and ileum than those measured at 60 min. Protein synthesis rates also tended to decline with time in the duodenum and colon (P > 0.05). There were no significant differences (P > 0.05) between protein synthesis rates calculated using the intracellular specific radioactivity vs. plasma specific radioactivity in the duodenum, ileum or colon. Therefore, this method represents an improvement over continuous infusion methods for measurements of protein synthesis in visceral tissues.

KEY WORDS: • sheep • protein synthesis • intestine • liver

¹ Presented in part at the 1990 Annual Meeting of the Canadian Society of Animal Science, Penticton, British Columbia [Southorn, B. G., Kelly, J. M. & McBride, B. W. (1990) Metabolic effects of "flooding doses" of phenylalanine in the sheep. Can. J. Anim. Sci. 770: 1201 (abs.)], the 1991 Annual Meeting of the Canadian Society of Animal Science, Fredricton, New Brunswick [Southorn, B. G., Kelly, J. M. & McBride, B. W. (1991) Protein synthesis measurements in sheep using a "flooding" dose technique. Can. J. Anim. Sci. 71: 1279 (abs.)] and the 1992 Annual Meeting of the Federation of American Societies for Experimental Biology, Anaheim, CA [Southorn, B. G., Kelly, J. M. & McBride, B. W. (1992) Evaluation of "flooding" dose methodology for the study of protein synthesis in the gastrointestinal tract. FASEB J. 6: A1966 (abs.)].

² Supported by a grant from the Natural Sciences and Engineering Research Council of Canada.

³ To whom correspondence should be addressed.

⁴ To whom reprint requests should be addressed.

Manuscript received 27 April 1992. Revision accepted 13 August 1992.

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