Kinetics of methionine influx into various regions of chicken intestine

Multiple pathways for L-methionine transport in brush-border membrane vesicles from chicken jejunum

1. The intestinal transport of L-methionine has been investigated in brush-border membrane vesicles isolated from the jejunum of 6-week-old chickens. L-Methionine influx is mediated by passive diffusion and by Na+-dependent and Na+-independent carrier-mediated mechanisms. 2. In the absence of Na+, cis-inhibition experiments with neutral and cationic amino acids indicate that two transport components are involved in L-methionine influx: one sensitive to L-lysine and the other sensitive to 2-aminobicyclo[2.2. 1]heptane-2-carboxylic acid (BCH). The L-lysine-sensitive flux is strongly inhibited by L-phenylalanine and can be broken down into two pathways, one sensitive to N-ethylmaleimide (NEM) and the other to L-glutamine and L-cystine. 3. The kinetics of L-methionine influx in Na+-free conditions is described by a model involving three transport systems, here called a, b and c: systems a and b are able to interact with cationic amino acids but differ in their kinetic characteristics (system a: Km = 2.2 +/- 0.3 microM and Vmax = 0.13 +/- 0.005 pmol (mg protein)-1 (2 s)-1; system b: Km = 3.0 +/- 0.3 mM and Vmax = 465 +/- 4.3 pmol (mg protein)-1 (2 s)-1); system c is specific for neutral amino acids, has a Km of 1.29 +/- 0.08 mM and a Vmax of 229 +/- 5.0 pmol (mg protein)-1 (2 s)-1 and is sensitive to BCH inhibition. 4. The Na+-dependent component can be inhibited by BCH and L-phenylalanine but cannot interact either with cationic amino acids or with alpha-(methylamino)isobutyrate (MeAIB). 5. The kinetic analysis of L-methionine influx under a Na+ gradient confirms the activity of the above described transport systems a and b. System a is not affected by the presence of Na+ while system b shows a 3-fold decrease in the Michaelis constant and a 1.4-fold increase in Vmax. In the presence of Na+, the BCH-sensitive component can be subdivided into two pathways: one corresponds to system c and the other is Na+ dependent and has a Km of 0.64 +/- 0. 013 mM and a Vmax of 391 +/- 2.3 pmol (mg protein)-1 (2 s)-1. 6. It is concluded that L-methionine is transported in the chicken jejunum by four transport systems, one with functional characteristics similar to those of system bo, + (system a); a second (system b) similar to system y+, which we suggest naming y+m to account for its high Vmax for L-methionine transport in the absence of Na+; a third (system c) which is Na+ independent and has similar properties to system L; and a fourth showing Na+ dependence and tentatively identified with system B.

Effect of heat stress on 2-hydroxy-4-(methylthio)butanoic acid and DL-methionine absorption measured in vitro

The objective of the present experiments was to determine the biochemical basis for preliminary chick performance data, which indicate an ameliorative effect of 2-hydroxy-4-(methylthio)butanoic acid (HMB) when compared with DL-methionine (DLM) fed during hot conditions. In vitro passage of HMB or DLM across intact segments of small intestine from either control (thermoneutral, TN) or heat-stressed (HS) birds was used as a model for intestinal absorption. For DLM placed in the lumen, appearance in the outside buffer was reduced when using intestine from HS birds compared with tissue from TN birds. In contrast, the appearance of HMB in the outside buffer was greater using HS intestine, resulting in a substrate by environment interaction (P < .01). Slices of everted small intestine from TN and HS birds were used to study epithelial uptake of methyl labeled 14C-DLM by three transport pathways: diffusion, carrier-specific energy- and sodium-independent uptake (ESI), and carrier-specific energy- and sodium-dependent uptake (ESD). Correcting for extracellular volume, total epithelial uptake of 14C-DLM (diffusion plus ESI plus ESD) was reduced by 34% in HS intestine (P < .05). Energy-dependent uptake was observed to decrease by 87% in HS (P < .05). Energy-independent uptake was increased (136%, HS versus TN, P < .05), but not enough to compensate for the decrease in ESD uptake. Intestinal transport systems for glucose and leucine were also observed to change during HS, suggesting a role for cellular transport changes in the performance reduction associated with HS.

Age influences on amino acid intestinal transport

1. Intestinal absorption of amino acids show a decrease with aging in different animal species such as avians, rodents and ruminants. 2. The different intestinal segments show different absorptive capacities, the jejunum being the most absorbent. 3. Chickens show the biggest capacity for amino acid absorption close to hatching. 4. In rodents the third week seems to be the period of increased transport capacity.

Regional differences for the d-amino acid oxidase-catalysed oxidation of d-methionine in chicken small intestine

1. Enzymic oxidation of D-[1-14C]methionine (D-met) to 2-keto-4-methylthiobutanoate (KMB) has been determined using 100,000 g supernatants prepared from chicken tissue homogenates. 2. The small intestinal mucosa contains substantial oxidative activity towards D-met, which represents about one-half and one-tenth the hepatic and renal activity, respectively. 3. KMB is poorly decarboxylated and rather transaminated to L-met. 4. The specific activity for D-met oxidation in the duodenal mucosa is 1.5- and 4.0-fold than in the jejunal and ileal mucosa, respectively. 5. The intestinal D-met-oxidizing activity is dramatically altered by the D-amino acid oxidase specific inhibitor benzoate.

Sugar and amino acid transport properties of the chicken ceca

Chickens have two well-developed ceca, with an epithelium that is histologically and functionally heterogeneous. The proximal region, close to the ileorectal junction, has well-developed villi and microvilli and is able to transport sugars and amino acids against a concentration gradient, by mechanisms virtually identical to those described for the small intestine. The medial-distal region does not have true villi but has mounds and ridges, and it cannot transport either sugars or amino acids in the adult bird. In newborn chicks, the whole cecum can accumulate and transport sugars, but this property is soon restricted to the proximal region. The medial cecum, however, retains some transport capacity until the 8th week after the hatch. Ceca are thus well suited for sugar and amino acid absorption. Their contribution to the overall nutrient absorption is, however, limited, because the absorbing epithelium is exposed to the intestinal contents only during the filling and emptying of the cecal segments.

Interspecific variation in sugar and amino acid transport by the avian cecum

Previous studies of cecal sugar and amino acid transport in the domestic chicken led to a widely held generalization that the avian cecum is unimportant as a site of nutrient transport. In fact, we found that the uptake capacity of the cecum for hexose sugars and amino acids is substantial in some species of birds. Cecal transport of glucose was measurable in all five study species (Canada goose, sage grouse, domestic chicken, red-necked phalarope, and rock dove), approached or exceeded intestinal levels in the grouse and phalarope, and accounted for between 0.1% (rock dove) and 49% (sage grouse) of the whole gut's integrated uptake capacity. Proline uptake averaged higher in the proximal portion of the cecum than in any region of the small intestine for all species but the goose. The ceca contributed between 2% (rock dove) and 25% (sage grouse) of the gut's integrated uptake capacity for proline. Similar ranges were found for fructose, lysine, leucine, and aspartate. Future studies should be undertaken to search for phylogenetic and ecological correlates of the interspecific variation in cecal transport and to determine how nutrient transport integrates with other functions of the avian cecum.

Na+-independent and nonstereospecific transport of 2-hydroxy 4-methylthiobutanoic acid by brush border membrane vesicles from chick small intestine

1. The transport of L- and DL-2-hydroxy 4-methylthiobutanoic acid (HMB), the methionine hydroxy analogue, by brush border membrane vesicles (BBMV) from chick small intestine was the sum of a saturable Michaelian component and a diffusive term. 2. Unlike that of L- and DL-MET, uptake was Na+-independent and electroneutral. 3. The inhibition of L-HMB transport by L-lactate, a structural analogue, and D-HMB as well, was of the competitive type. 4. Preloading of BBMV with D-HMB but not with L-lactate or L-MET trans-stimulated the influx of labelled L-HMB. 5. HMB uptake by rat and chick intestinal BBMV exhibited similar characteristics but the chick nonstereospecific transport system appeared to be unable to carry out L-lactate translocation.

Ammonia production from uric acid, urea, and amino acids and its absorption from the ceca of the cockerel

Experiments were conducted in situ and in vitro in the ceca to measure ammonia production from uric acid, urea, and amino acids and its absorption. When uric acid was injected into a cecal sac containing mixed cecal microfloras, 77% disappeared within 1 hour, with a concomitant increase in ammonia concentration. When [15N]uric acid was added to the ceca in situ, 28% was converted to ammonia after 30 minutes. About 92% of the ammonia introduced into a cecal sac disappeared from the lumen fluid within 30 minutes. About 43% of each of urea nitrogen and glutamine-amide nitrogen was converted to ammonia-nitrogen, and 25% of uric acid-nitrogen and epsilon nitrogen of the arginine was found in ammonia. The conversion of aminonitrogen of glutamic acid and glycine to ammonia amounted to 19-20%, whereas that of alpha-alanine totaled 11%. It is concluded that dietary and urinary nitrogenous compounds that find their way into the ceca are useful nitrogen sources for ammonia production by microflora in the ceca of the chicken, and that ammonia is absorbed rapidly from the ceca.

Hexose transport by chicken cecum during development

Hexose accumulation during development has been studied in tissue slices from chicken cecum. The age of birds ranged from 0 to 7 weeks after hatch. Ceca were divided into six portions according to their situation either proximal (PC), medial (MC) or distal (DC) to the ileocecal junction. In 0-day-old chicks all segments can accumulate 3-O-methyl-D-glucose (0.5 mmol/l) against a concentration gradient through a phloridzin-sensitive mechanism. Cumulative capacity is lower in DC than in PC and declines with development. Distal segments lose sugar transport ability 1-2 days after hatch whereas the medial region retains some concentrative ability in older birds. In 7-week chickens, PC slices have a similar cumulative ability to that of jejunum (yolk sac region). Kinetic studies showed that in PC the apparent Km for phloridzin-sensitive transport was half that in 1-day- than in 7-week-old birds; apparent Vm increased by 50% in this time range. The ability to transport sugars by the cecum was further confirmed in isolated enterocytes from 5- to 7-week-old chickens using alpha-methyl-D-glucoside (0.1 mmol/l) as substrate. Cell sugar concentration was greater in PC than in jejunal cells and jejunal greater than MC enterocytes. Sugar present in cells from DC was the same as in phloridzin-treated cells. It is concluded that cecal epithelium may play a significant role in the absorption of sugars during development.

Characteristics of the chicken proximal cecum hexose transport system

The properties of the sugar transport system present in chicken proximal cecum have been studied and compared to the jejunal transport system. Experiments were carried out in isolated enterocytes from 5- to 7-weak-old birds. Results show that: (1) Cecal cells are capable of high sugar transport rates by a phloridzin-sensitive mechanism. After 60 min incubation, the accumulation ratio (control/phloridzin-incubated cells) for 0.1 mmol/l alpha-methyl-D-glucoside (alpha-MG) was 43 and that of 3-oxy-methyl-D-glucose (3-OMG) was 25. In jejunal cells, ratios were 37 for alpha-MG and 13 for 3-OMG. The differences found in cumulative capacity of 3-OMG between cecal and jejunal cells suggest that the sodium-independent pathway offers a very small contribution to sugar efflux in the steady-state in the former cells. (2) Lowering external Na+ concentration reduces the steady-state alpha-MG accumulation in cecal cells (as in jejunal cells), indicating that the transport system is Na+-dependent. (3) The process depends on the electrochemical Na+ gradient across the cell membrane since both 2,4-dinitrophenol (0.2 mmol/l) and ouabain (0.25 mmol/l) abolish sugar accumulation. (4) Addition of 10 mmol/l) 3-OMG to the incubation medium markedly reduces the uptake of alpha-MG (concentration: 0.1 mmol/l), indicating that the cecal transport system can be inhibited by analogues of the transported substrate. (5) The specific sugar transport process is a saturable function of alpha-MG concentration, the apparent Km being 1.02 mmol/l and Vm 10.7 mmol/mg cell protein X min.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption of 3-oxy-methyl-D-glucose by chicken cecum and jejunum in vivo

Jejunal and cecal 3-oxy-methyl-D-glucose (3-OMG) absorption was studied in 4- to 8-week-old chickens by an in vivo perfusion technique (perfusion rate 1.5 ml/min). Total and phloridzin-insensitive 3-OMG absorption was tested for lumenal substrate concentrations ranging from 1.25 to 20 mmol/l. The estimated apparent Michaelis constants in jejunum and cecum were 5.1 and 4.0 mmol/l (Lineweaver-Burk method) and 3.2 and 3.1 mmol/l (visual inspection method), respectively. Vmax were similar in both segments with either method, about 0.3 mumol/cm2 X 5 min. Passive permeability coefficients were the same in both regions (about 45 l/cm2 X 5 min X 10(3)). The transport properties of the cecal epithelium in vivo suggest a role of these intestinal segments in the absorption of nutrients originated from digestive processes.

Cell membrane amino acid transport processes in the domestic fowl (Gallus domesticus)

Intestinal absorption of amino acids in the chicken occurs by way of processes which are concentrative, Na+-dependent and dependent upon metabolic energy in the form of ATP. Intestinal transport is carrier-mediated, subject to exchange transport (trans-membrane effects) and is inhibitable by sugars, reagents which inactivate sulfhydryl groups, potassium ion, and by deoxpyridoxine, an anti-vitamin B6 agent. It is stimulated by phlorizin, a potent inhibitor of sugar transport, and in Na+-leached tissue by modifiers of tissue cyclic AMP levels, e.g. theophylline, histamine, carbachol and secretin. Separate transport sites with broad, overlapping specificities function in the intestinal absorption of the various classes of common amino acids. A simple model for these sites includes one for leucine and other neutral amino acids, one for proline, beta-alanine and related imino and amino acids, one for basic amino acids, and one for acidic amino acids. Absorption of amino acids appears to be widespread in occurrence in the digestive tract of the domestic fowl; transport has been reported to be present in the crop, gizzard, proventriculus, small intestine and in the colon. By the end of the first week of life post-hatch, the caecum loses its ability to transport. Similarly, the yolk sac loses its ability by the second day post-hatch. Intestinal transport was noted before hatch and was found to be maximal immediately post-hatch. A requirement for Ca2+ appears to be lost after the first week of life post-hatch. The cationic amino acids appear to be reabsorbed by a common mechanism in the kidney. Transport rates of leucine measured in the intestine or in the erythrocyte were found to cluster about discrete values when many individual chickens were surveyed; such patterns may be an expression of gene differences between individuals. Two lines of chickens have been developed, one high and the other low uptake, through selective breeding based on the ability of individual birds to absorb leucine in erythrocytes. High leucine absorbing chickens were found to be more effective in absorbing lysine and glycine, were more effectively stimulated by Na+, had greater erythrocyte Na+, K+-ATPase activity, and their erythrocytes contained about 20% less Na+ than low line erythrocytes. The underlying genetic difference between these lines may reside at the level of the Na+, K+-ATPase and (or) with a regulatory gene determining carrier copies. Amino acid transport in erythrocytes was noted to be highest in pre-hatch chicks and to diminish during post-hatch development.(ABSTRACT TRUNCATED AT 400 WORDS)

Avian species differences in the intestinal absorption of xenobiotics (PCB, dieldrin, Hg2+)

Intestinal absorption of a polychlorinated biphenyl, dieldrin, and mercury (from HgCl2) was measured in adult Northern bobwhites, Eastern screech owls, American kestrels, black-crowned night-herons and mallards in vivo by an in situ luminal perfusion technique. bobwhites, screech owls and kestrels absorbed much more of each xenobiotic than black-crowned night-herons and mallards. Mallards absorbed less dieldrin and mercury than black-crowned night-herons. Mercury absorption by kestrels was more than twice that in screech owls and eight times that observed in mallards. Pronounced differences in xenobiotic absorption rates between bobwhites, screech owls and kestrels on the one hand, and black-crowned night-herons and mallards on the other, raise the possibility that absorptive ability may be associated with the phylogenetic classification of birds.

Developmental changes in amino acid transport in the chicken erythrocyte

1. Influx of leucine, lysine and glycine was found to be highest in prehatch (day -1) chicken red blood cells and to diminish during posthatch development when tested at two and four weeks of age. 2. The greatest decline in transport rate during development was seen with leucine; lysine showed a substantial age-related decline only at substrate concentrations greater than Km, the apparent Michaelis constant of transport. 3. Vmax, the maximal transport influx, of each amino acid tested declined during development. 4. Km of glycine and leucine appeared to increase slightly over the test period. 5. In contrast, a 7-fold decrease in Km for lysine transport was seen over the same period. 6. These results are discussed in context of changes in kinetic parameters of amino acid transport during development reported for various animal organs or tissues.

Amino acid absorption in jejunum and ileum in vivo -- a kinetic comparison of function on surface area and regional bases

Maximum absorptive capacities (Vmax) for the jejunum and ileum corrected for the presence of an unstirred layer of water have been calculated for glycine, valine and methionine in vivo in fowls per unit surface area and per region. Vmax per cm2 showed that ileal enterocytes had a greater absorbing capacity than jejunal for glycine and valine but not for methionine. Vmax for glycine and valine, calculated for the whole jejunum and ileum, however, were not different but for methionine the jejunal value was 1.9 times greater than the ileal.

Effects of dietary intake of sodium chloride on sugar and amino acid transport across isolated hen colon

1. Using the isolated mucosa from the colon of the adult hen, transport of galactose, leucine and lysine was studied through measurements of influx across the brush-border membrane, unidirectional transmucosal fluxes, and of steady-state mucosal uptake.2. In hens maintained on a NaCl rich diet influx of galactose, leucine and lysine were saturable processes with well defined values for J(max) and K(t). All three substances were actively transported across the epithelium and accumulated in the mucosal tissues to steady-state concentrations several times higher than in the incubation media.3. In hens maintained on a NaCl poor diet the K(t) of the leucine influx was markedly increased and the J(max) moderately decreased, while the epithelium maintained the capability of active transepithelial transport and of establishing a steady-state tissue/medium distribution ratio well above 1. Galactose and lysine could no longer be actively transported and in the steady state their tissue concentrations did not exceed those of the medium.4. It is proposed that in the low NaCl colon the processes of galactose and lysine co-transport with Na are abolished and that the transport of galactose proceeds via a phloretin sensitive system like that described for the enterocyte of the chicken small intestine.5. In the high NaCl colon 1 mM-leucine increases the mucosa to serosa flux of lysine by a factor 2.8 without affecting the serosa to mucosa flux or the steady-state mucosal accumulation of lysine. In the low NaCl colon 1 mM-leucine induces active transepithelial transport of lysine. Assuming that the active transport of leucine is secondary to the transport of Na, leucine-induced active transport of lysine is described as a tertiary active transport.6. In the high NaCl colon the mucosa to serosa flux and the steady-state mucosal accumulation of leucine were inhibited by galactose which had no effect on leucine influx across the brush-border membrane. Leucine did not affect any of the parameters of galactose transport.

Methionine transport by pig colonic mucosa measured during early post-natal development

New-born pig proximal colon, incubated in vitro, transports methionine with a Km of 0-33 mM and a Vmax of 0-62 mumole cm-2h-1. There is still a net transport of methionine on day 4, but the Km now increases to 10 mM and the Vmax falls to 0-15 mumole cm-2h-1. There is no net transport of methionine across proximal colons taken from 10-day-old pigs. 2. The mean intramucosal concentration of methionine, following incubation in medium containing 1 mM methionine, is 7-18+/-0-8 mM for the new-born, 0-55+/-0-05 mM for the 4-day-old and 0-31+/-0-06 mM for the 10-day-old pig. 3. Both methionine and glucose cause an immediate increase in the short-circuit current of new-born and 1-day-old pig colons. The kinetics for this interaction with methionine gives a Km for methionine of 0-24 mM and a maximum effect of 27 muA cm-2. This effect is not seen in 4- or 10-day-old pigs. 4. Net Na+ transport across the new-born pig proximal colon, measured in the absence of methionine, is about three times that calculated from the measured short-circuit current. Methionine increases the mucosal to serosal flux of Na+ by an amount roughly equal to that predicted from the increase in short-circuit current. The ability of glucose and methionine to affect short-circuit current is lost by day 4. 5. Short-circuit current, measured in the absence of methionine or glucose, increases between day 1 and 2 of post-natal life. This increased electrogenicity is maintained for up to at least 10 days after birth. 6. The pig proximal colon has many of the properties of a small intestine at birth. It actively transports methionine and the presence of methionine stimulates the absorption of Na+. These effects could be physiologically important in the pig, where the normal absorptive function of the intestine is temporarily inhibited at birth by the intestinal transmission of immune globulins.