Absorption of amino acids from the intestine and their net flux across the mesenteric- and portal-drained viscera of lambs.

Abstract

Experiments were conducted to compare the rates of apparent absorption (disappearance) of individual essential amino acids (EAA) from the small intestine with their net fluxes across the mesenteric- (MDV) and portal- (PDV) drained viscera in sheep given a pelleted alfalfa diet at two levels of intake. Disappearances of individual EAA across the region of the small intestine drained by the mesenteric arcade (jejunum to ileum) were similar to those across the whole of the small intestine (duodenum to ileum). The net MDV flux of each EAA was similar to its rate of disappearance, but, with the exception of threonine on the low intake level, the net PDV flux was lower (P < .05). Increasing the intake of alfalfa from 800 to 1,200 g/d increased the rate of disappearance of individual EAA between the duodenum and ileum by .56 (range .43 to .65) and between the jejunum and ileum by .51 (range .45 to .60). The MDV and PDV blood flows increased by .35 and .39, respectively, and, with the exception of valine, net fluxes of individual EAA increased by .39 (range .20 to .50) across the MDV and by .44 (range .21 to .71) across the PDV. When net fluxes across the MDV and PDV were measured simultaneously, the ratio of PDV: MDV flux for each EAA was less than (P < .05) unity (mean .61, range .55 to .69), even though all MDV blood enters the PDV, contributing approximately .45 of the total portal flow. This observation suggests that, in regions of the tract not drained by the MDV, extraction of arterial blood EAA for tissue and secretory protein synthesis must exceed the release of protein degradation products into the venous drainage. The results are discussed in terms of endogenous protein secretions into the lumen of the tract anterior to the small intestine.

Intestinal amino acid absorption in lambs fed fresh Lucerne (Medicago sativa) during an established Trichostrongylus colubriformis infection

“…This suggests an increase in AA disappearance from the small intestine of the infected lambs, although the apparent absorption from the small intestine and net flux of AA across the MDV were similar between treatments. The net flux of AA across the MDV in the current study (1 to 5 g/day) is similar to the 4 to 6 g/day reported by MacRae et al (1997b) at similar intakes, but the similar net fluxes of AA across the MDV between control and parasitised lambs contrast with the observations for leucine by Yu et al (2000). While mesenteric plasma flows are within the ranges in the literature for sheep at a similar age and DM intake (700 to 1000 ml/min; Janes et al, 1985;MacRae et al, 1997b;Yu et al, 2000;Bermingham et al, 2007b), they are highly variable (CV of 28% to 40% in the control and parasitised lambs, respectively), and this variability may have masked any effects of infection on MDV AA fluxes.…”

“…The net flux of AA across the MDV in the current study (1 to 5 g/day) is similar to the 4 to 6 g/day reported by MacRae et al (1997b) at similar intakes, but the similar net fluxes of AA across the MDV between control and parasitised lambs contrast with the observations for leucine by Yu et al (2000). While mesenteric plasma flows are within the ranges in the literature for sheep at a similar age and DM intake (700 to 1000 ml/min; Janes et al, 1985;MacRae et al, 1997b;Yu et al, 2000;Bermingham et al, 2007b), they are highly variable (CV of 28% to 40% in the control and parasitised lambs, respectively), and this variability may have masked any effects of infection on MDV AA fluxes. High variability (.25%) in blood flow across the MDV has been observed previously (MacRae et al, 1997b;Yu et al, 2000), and might be attributed to either incomplete mixing of the dye in those blood vessels or movement of the catheter due to peristaltic intestinal contractions (MacRae et al, 1997b).…”

Post-ruminal or intravenous infusions of carbohydrates or amino acids to dairy cows 1. Early lactation

“…Thus, abomasal infusion will probably reduce the AA available for milk production compared with intravenous infusions. It has been shown that there is a high rate of energy and protein turnover in the lumen wall and the PDV (Cant et al, 1996;Reynolds, 2002) and that there is a substantial metabolism of EAA during absorption by intestinal enterocytes (MacRae et al, 1997). Elevated luminal nutrient supply has shown to influence activity which promotes tissue growth (Cant et al, 1996).…”

Strategies for optimizing nitrogen use by ruminants

“…These measurements represent the net supply of AA after metabolism by the PDV during absorption and from arterial blood. As the PDV is a heterogonous collection of tissues, including the small intestine, reticulorumen, hindgut, pancreas, muscle and other tissues that do not have access to the AA during their absorption, measurement of net mesenteric-drained viscera (MDV; the tissues drained by the cranial mesenteric vein) release of AA provides a closer approximation of the true supply of AA from the small intestine, especially for sheep (MacRae et al, 1997b;Ré mond et al, 2003). In sheep, the net PDV release of EAA represented about 65% of the net release across the MDV, reflecting the uptake of EAA from arterial blood by the reticulorumen and other tissues not drained by the cranial mesenteric vein.…”