Net flux of amino acids across splanchnic tissues of ewes during abomasal protein and glucose infusion

Authors: Freetly, Harvey; Ferrell, Calvin; ARCHIBEQUE, SHAWN - COLORADO STATE UNIVERSITY

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/6/2007
Publication Date: 8/1/2007
Citation: Freetly, H.C., Ferrell, C.L., Archibeque, S.L. 2007. Net flux of amino acids across splanchnic tissues of ewes during abomasal protein and glucose infusion. Proceedings of Energy and Protein Metabolism and Nutrition, EAAP Publication No. 124. p. 337-338.

Interpretive Summary:

Technical Abstract: Introduction Studies in sheep (MacRae et al., 1997) and in pigs (Stoll et al., 1998) indicated approximately one-third of the amino acids absorbed by the enterocyte are metabolized within the enterocyte and are never released into the blood. Of those amino acids that are metabolized, 60% are apparently catabolized (Stoll et al., 1998) suggesting that 20% of the absorbed amino acids are catabolized for energy within the enterocyte. A potential mechanism to reduce amino acid catabolism by enterocytes is to provide an alternative energy source. We hypothesized that amino acid catabolism within enterocytes can be reduced by elevating glucose availability to enterocytes, resulting in increased net appearance of amino acids in portal vein blood. Materials and Methods Eighteen Dorset ewes (71.7 ± 0.7 kg) were individually penned and fed a pelleted diet (95% brome hay and 5% soybean meal, as DM) at a level of 52.2 g/BW kg0.75. The diet was 10% CP and had a calculated ME of 1.96 Mcal/kg, as DM. Ewes were fed a single meal daily at 1500 h. Catheters were placed in the hepatic portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta (Freetly and Ferrell, 1998). Glucose and protein were infused into an abomasal canula. Ewes either received glucose (3.84 g/h) or glucose-free (Control) infusions along with one of five protein infusions. Each ewe remained on assigned glucose treatments and received all five protein infusions in a replicated Latin square design within treatment. The protein infusions consisted of isolated soy protein (Ardex® F Dispersible, Archer Daniels Midland Company, Decatur, IL 62525) and cysteine 8.26% by weight). The infusion levels were 0, 2.616, 5.232, 7.848, and 10.464 g/h Ardex + cysteine. The calculated amino acid equivalents were 0, 18.1, 36.3, 54.4, and 72.6 mmol/h. Abomasal infusions were started 17 h after the meal. Para-amino hippuurc acid (PAH, 0.15 M) was infused into the mesenteric vein (0.8 mL/min). Four hours after abomasal infusions were initiated, blood samples were drawn at 30-minute intervals for a total of five sets of samples. Whole blood was analyzed for PAH and glucose (Freetly and Ferrell, 1998). Glutamate and glutamine concentrations were determined on a membrane-immobilized system (Model 2700; Yellow Spring Instrument Co., Yellow Springs, OH). Blood amino acids were analyzed according to the procedure of Calder et al. (1999). Net fluxes were calculated by application of the Fick principle described by Freetly and Ferrell (1998). Data were analyzed by use of a split-plot model. All fluxes were tested with a full model that included animal nested within treatment, treatment, (protein level)2, protein level, treatment × (protein level)2, and treatment × (protein level). Protein level was treated as a continuous effect. A step-down regression approach was used to determine the model that best described the regression coefficients for net fluxes on protein level. Results and Discussion Net portal-drained viscera (PDV) lysine release (P = 0.05; 2.33 ± 0.48 vs. 1.04 ± 0.49 mmol/h) and net histidine release (P = 0.04; 1.29 ± 0.43 vs. 0.24 ± 0.43 mmol/h) increased in glucose infused ewes compared to controls. Net PDV release of other amino acids did not differ with glucose infusion (P > 0.13). Net PDV release of alanine (2.11 ± 0.23 mmol/h; P = 0.10) glycine (2.03 ± 0.17 mmol/h; P = 0.69), histidine (P = 0.84), lysine (P = 0.21), threonine (0.84 ± 0.09 mmol/h; P = 0.11), valine (1.07 ± 0.09 mmol/h; P = 0.13) did not differ with abomasal amino acid infusion; however, net release of other amino acids increased linearly (Table 1). Net PDV release of glucose was greater (P < 0.001) in ewes that received the glucose infusion [f(x) = -0.0026x2 + 0.161x + 1.6] compared to controls [f(x) = -0.0026x2 + 0.161x -12.9] and the rate increased with increa