Free and peptide amino acid net flux across the rumen and the mesenteric- and portal-drained viscera of sheep.

Abstract

This experiment was conducted to determine the significance of the peptide amino acid (PAA) contribution to amino acid (AA) net flux in the portal vein and to evaluate the capacity for peptide absorption in the different segments of the gastrointestinal tract of ruminants. Four sheep (64+/-3 kg BW) were fitted with catheters and blood flow probes, allowing AA net flux measurements across the portal- (PDV) and mesenteric (MDV)-drained viscera and the rumen. Sheep were fed at maintenance a diet containing hay and extruded peas (70:30). Peptide absorption was investigated by a dose infusion of a mixture of peptides (casein hydrolysate, Pro-Phe, beta-Ala-His, Gly-Gly) into the rumen. Control and postinjection net fluxes of plasma free amino acids (FAA) and PAA were determined. The concentration of plasma PAA was determined by quantification of amino acids before and after acid hydrolysis of samples first submitted to chemical deproteinization and ultrafiltration (3-kDa cut-off filter). During the control period a significant net release (12 mmol/h) of PAA was observed across the PDV, which accounted for 35% of the sum of FAA and PAA net fluxes. This PDV flux of PAA mainly resulted from a MDV release of PAA (15 mmol/h). The net flux of total PAA across the ruminal wall was not significantly different from zero, but uptake of peptide Ile and release of peptide Gly were observed. The injection into the rumen of the peptide mixture increased the net release of peptide essential AA (EAA) across the MDV (P < .05) and the PDV (P < .10), and of peptide Pro and Phe across the non-MDV (P < .10). Peptide Ile uptake by the rumen tissues was decreased by the injection (P < .05). Significant increases in peptide Pro and Gly arterial concentrations were observed (P < .05). The 3-Ala-His and Gly-Gly arterial concentrations and net fluxes across the PDV were not affected by their injections into the rumen. This study showed that PAA may contribute significantly to AA flux across the PDV of sheep, and that part of this flux can probably be attributed to peptide absorption from the gut lumen. When high concentrations of peptides are generated in the rumen the possibility of peptide absorption before the jejunum has to be considered.

Digestion and nutrient net fluxes across the rumen, and the mesenteric- and portal-drained viscera in sheep fed with fresh forage twice daily: net balance and dynamic aspects

“…The rumen and MDV blood flows observed in the present experiment accounted for 18 and 23 % of the PBF, respectively. The rumen contribution to PBF is within the range of reported values (from 13 to 22 %; Barnes et al 1983;Rémond et al 2000b;Han et al 2002). The MDV contribution is in agreement with previous studies in sheep, where BF in the cranial mesenteric vein (upstream of the junction with the ileocaecocolic vein) was recorded with transittime ultrasonic probes (Neutze et al 1994;Rémond et al 2000b) or with the microsphere technique (Barnes et al 1983).…”

“…The rumen contribution to PBF is within the range of reported values (from 13 to 22 %; Barnes et al 1983;Rémond et al 2000b;Han et al 2002). The MDV contribution is in agreement with previous studies in sheep, where BF in the cranial mesenteric vein (upstream of the junction with the ileocaecocolic vein) was recorded with transittime ultrasonic probes (Neutze et al 1994;Rémond et al 2000b) or with the microsphere technique (Barnes et al 1983). However, a greater contribution (45 % of PBF) was observed by MacRae et al (1997b) using the dye dilution technique; such a contribution was more generally attributed to the whole intestine (Neutze et al 1994;Han et al 2002).…”

“…Total N apparently digested in the digestive tract was 15·6 g N/d while the summation of portal FAA, PAA, NH 3 and urea net fluxes (11·3, 3·5, 10·4, and 2 10·3 g N/d, respectively) was 14·9 g N/d. Such a close relationship between digestive and portal net balance of N was previously reported by Rémond et al (2000b). However, these balances have to be manipulated cautiously, first because PDV measurements do not take into account salivary and biliary N secretions into the gut, and second because the net release of protein-N, high-molecular-weight peptide-N, and N from nucleic bases across the PDV was not considered.…”

“…Blood VFA analysis was carried out as described by Nozière et al (2000a). Peptide amino acid (PAA) determination in plasma was achieved according to the work of Rémond et al (2000b). Bernard et al (2001) has already discussed the choice of this technique.…”

“…After pH measurement, rumen fluid was centrifuged (800 g for 10 min at 48C), and the supernatant fraction was then centrifuged at 27 000 g for 20 min at 48C. The supernatant fraction was sub-sampled for analyses of VFA, NH 3 -N, FAA and PAA as described by Rémond et al (1993aRémond et al ( , 2000b.…”