Quantification of circulating peptides and assessment of peptide uptake across the gastrointestinal tract of sheep.

Abstract

Gastrointestinal absorption of peptides was examined in sheep fed a forage-based diet. Peptide concentrations were determined in arterial, portal, and mesenteric blood and plasma by quantification of amino acid concentrations before and after acid hydrolysis of samples that had been first deproteinized then subjected to Sephadex G-15 gel-filtration to remove residual protein. In contrast to other studies of ruminants, peptide concentrations for individual amino acids were lower than for the corresponding free amino acids with peptide (expressed as a proportion of total nonprotein amino acid) representing not more than .25 to .3 of total amino acid. Peptide concentrations in arterial, mesenteric, and portal blood and plasma were similar, indicating that on this diet there was no net uptake of peptides from the small intestine (mesenteric-drained viscera, MDV) or the whole tract (portal-drained viscera, PDV). Increasing the intake of alfalfa pellets from 800 to 1,200 g/d, while increasing the absorption and net flux across the MDV and PDV of free amino acids, had no effect on peptide absorption. Preparation of blood and plasma samples for peptide analysis with methods used in studies in which substantial peptide absorption has been reported indicated no net MDV or PDV flux of peptide. Such conflicting data on the extent of gastrointestinal peptide flux are discussed in the context of methodological differences and the importance of diet and physiological state of the animal.

Preparation of a polyclonal antibody against immunogenic fragment of bovine intestinal peptide transporter I (<i>b</i>PepTI)

“…In calves, for example, it has been shown that small peptides constituted 79% of total amino acid absorbed into portal vein in calves [9]. In sheep, however, no small peptide was found to be absorbed into portal vein [10]. Although differences in the results among these studies are attributable to species and diet, more important reason may be due to the inaccurate nature of the flux determination methods.…”

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

“…In the present study with sheep fed fresh forage it accounted for 25 %. In sheep fed lucerne pellets (Backwell et al 1997;Bernard et al 2002) no significant flux of PAA across the PDV tissues could be detected. Combined, these data suggest that, in adult sheep, the significance of low-molecular-weight peptide net flux across the PDV is related to the nature of the diet.…”

In Vitro Transfer of L-Alanine, L-Histidine, and Carnosine Across Rumen Epithelium of Sheep

“…Peptide absorption from the stomach was postulated to explain this phenomenon. However, in another study (Backwell et al 1997), no significant release of peptide amino acids was observed in the mesenteric vein or in the portal vein. Thwaites et al (1993) showed the presence of the proton-coupled peptide transporter in the epithelial tissues on both the apical and basolateral membranes in the gut.…”