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PubMed1991

A simple test of intestinal absorption of calcium in rats.

We have developed a simple test of fractional calcium absorption in rats using oral 45Ca. The tracer was administered via a gastric tube, each animal receiving 0.15 microgram 45Ca with calcium glubionate as a carrier. Plasma radioactivity was determined at 30, 60, 90 and 120 min and expressed as percent dose in extracellular fluid. The fractional absorption of 45Ca was also expressed as 'area under the curve' (F45Ca) calculated by Simpson's approximation for each rat. The fractional absorption of calcium was determined in fasting and nonfasting fed animal subsets, each subset including control and rats treated with 1,25(OH)2D3. After 1,25(OH)2D3 administration, a significant increase in plasma calcium was seen in both fasting and fed animals. The fractional absorption of calcium was significantly higher in 1,25(OH)2D3-treated fasting as compared with control rats. In these animals, a positive correlation was found between F45Ca and plasma calcium. In contrast, in fed rats, the determined fractional absorption of calcium was similar in control and after 1,25(OH)2D3 administration. These results point to the use of orally administered 45Ca as a technically easy method for calcium absorption which can be used in most laboratories. In fasting animals it is sensitive enough for the evaluation of the effect of promoters of calcium absorption. The different findings in fed and fasting states may be related to the transmural processes which regulate the intestinal absorption of calcium.

Animals↗
PubMed1986

Colonic absorption of sulfated and nonsulfated bile acids in rat.

Absorption of sulfated and nonsulfated chenodeoxycholic and glycochenodeoxycholic acid was studied in the colon and the data were compared with the absorption rates in the ileum. Absorption of nonsulfated chenodeoxycholic acid in the colon was in the same range of magnitude as in the ileum. Glycochenodeoxycholic acid absorption in the colon was lower than in the terminal ileum. Sulfated bile acids were not absorbed in the colon. In the ileum, absorption of sulfated bile acids was significantly (p less than 0.01) lower than the absorption of nonsulfated bile acids. Little absorption of sulfated bile acids in the ileum and lack of absorption in the colon both contribute to the rapid turnover and excretion of bile acid sulfates.

Animals↗
PubMed1967

Absorption of cholesterol from a micellar solution: intestinal perfusion studies in man.

The absorption of cholesterol has been studied in man by perfusing the upper jejunum with a micellar solution of bile salt, 1-monoglyceride, and cholesterol-(14)C, with a triple lumen tube with collection sites 50 cm apart. The absorption of micellar components between the collection sites was calculated from their concentration changes relative to those of the watersoluble marker, polyethylene glycol. Control experiments were performed with cholesterol-free perfusions of saline or bile salt-monoglyceride solutions. Steady state conditions were obtained.Each of the components of the micelle was absorbed to a different extent during passage through the test segment of jejunum. Bile salt was not absorbed (mean, -3%), but micellar monoglyceride was rapidly hydrolyzed and absorbed almost completely (mean, 98%). Cholesterol radioactivity was absorbed to an intermediate extent (mean, 73%), and the absorption of chemically determined cholesterol (mean, 46%) indicated that much of the disappearance of radioactivity represented true absorption and not simple exchange. The specific activity of the perfused cholesterol fell during passage through the loop. This fall was interpreted as signifying the continuous addition of nonradioactive endogenous cholesterol by the test segment. However, the decrease in specific activity may also be considered to signify exchange, in that nonradioactive molecules entered the lumen as radioactive molecules were absorbed. Plant sterols appeared in the intestinal contents during the perfusion and must have been contributed by the perfused segment. The perfusate and samples taken from the upper and lower collection sites were examined by ultracentrifugation to define the physical state of cholesterol. It was found that cholesterol in the perfusate or upper collection site samples did not sediment, but that 23% of the cholesterol in the lower collection site samples was sedimentable (mean of three experiments); bile salt, as control, was not sedimentable. Solubility experiments in model systems showed that cholesterol possessed low solubility in bile salt solution; its solubility increased markedly and in linear proportion to the amount of fatty acid or monoglyceride or both that was added to the bile salt solution. These findings suggest that polar lipid such as fatty acid or monoglyceride as well as bile salt is essential for normal micellar solubilization of cholesterol in intestinal content. They suggest the necessity of considering an insoluble sedimentable phase of particulate sterol in intestinal content as well as an oil and micellar phase for a complete description of sterol absorption. The marked difference in the rates of absorption of individual micellar components suggests that micellar lipid is not absorbed as an intact aggregate and is consistent with the view that polar lipid such as fatty acid is absorbed in molecular form by diffusion from a micellar solution. The experiments confirm previous findings demonstrating that fat absorption without bile salt absorption occurs in the upper small intestine in man.

Adult↗
PubMed1967

Absorption of bile pigments by the gall bladder.

A technique is described for preparation in the guinea pig of an in situ, isolated, vascularized gall bladder that exhibits normal absorptive functions. Absorption of labeled bile pigments from the gall bladder was determined by the subsequent excretion of radioactivity in hepatic bile. Over a wide range of concentrations, unconjugated bilirubin-(14)C was well absorbed, whereas transfer of conjugated bilirubin proceeded slowly. Mesobilirubinogen-(3)H was absorbed poorly from whole bile, but was absorbed as rapidly as unconjugated bilirubin from a solution of pure conjugated bile salt. Bilirubin absorption was not impaired by iodoacetamide, 1.5 mM, or dinitrophenol, 1.0 mM, even though water transport was affected. This indicated that absorption of bilirubin was not dependent upon water transport, nor upon energy-dependent processes. The linear relationship between absorption and concentration of pigment at low concentrations in bile salt solutions suggested that pigment was transferred by passive diffusion. At higher pigment concentrations or in whole bile, this simple relationship was modified by interactions of pigment with bile salts and other constituents of bile. These interactions did not necessarily involve binding of bilirubin in micelles. The slow absorption of the more polar conjugates and photo-oxidative derivatives of bilirubin suggested that bilirubin was absorbed principally by nonionic, and partially, by ionic diffusion. Concentrations of pure conjugated bile salts above 3.5 mM were found to be injurious to the gall bladder mucosa. This mucosal injury did not affect the kinetics of bilirubin absorption. During in vitro incubation of bile at 37 degrees C, decay of bilirubin and hydrolysis of the conjugate proceeded as first-order reactions. The effects of these processes on the kinetics of bilirubin absorption, and their possible role in the formation of "white bile" and in the demonstrated appearance of unconjugated bilirubin in hepatic bile, are discussed.

Absorption↗
PubMed1968

The mechanisms of sodium absorption in the human small intestine.

The present studies were designed to characterize sodium transport in the jejunum and ileum of humans with respect to the effects of water flow, sodium concentration, addition of glucose and galactose, and variations in aniomic composition of luminal fluid. In the ileum, sodium absorption occurred against very steep electrochemical gradients (110 mEq/liter, 5-15 mv), was unaffected by the rate or direction of water flow, and was not stimulated by addition of glucose, galactose, or bicarbonate. These findings led to the conclusion that there is an efficiently active sodium transport across a membrane that is relatively impermeable to sodium. In contrast, jejunal sodium (chloride) absorption can take place against only the modest concentration gradient of 13 mEq/liter, was dramatically influenced by water movement, and was stimulated by addition of glucose, galactose, and bicarbonate. The stimulatory effect of glucose and galactose was evident even when net water movement was inhibited to zero by mannitol. These observations led to the conclusion that a small fraction of jejunal sodium absorption was mediated by active transport coupled either to active absorption of bicarbonate or active secretion of hydrogen ions. The major part of sodium absorption, i.e. sodium chloride absorption, appeared to be mediated by a process of bulk flow of solution along osmotic pressure gradients. The stimulatory effect of glucose and galactose, even at zero water flow, was explained by a model in which the active transport of monosaccharide generates a local osmotic force for the absorption of solution (NaCl and water) from the jejunal lumen, which, in the presence of mannitol, is counterbalanced by a reverse flow of pure solvent (H(2)O) through a parallel set of channels which are impermeable to sodium. Support for the model was obtained by the demonstration that glucose and bicarbonate stimulated the absorption of the nonactively transported solute urea even when net water flow was maintained at zero by addition of mannitol to luminal contents.

Adult↗
PubMed1973

Effect of luminal sodium concentration on bicarbonate absorption in rat jejunum.

An exchange of Na(+) for H(+) has been proposed to explain why jejunal Na(+) absorption is influenced by luminal concentrations of H(+) and HCO(3) (-). We studied the influence of luminal Na(+) concentration on net HCO(3) (-) absorption by perfusing rat jejunum in vivo. When Na(+) was omitted from the perfusion fluid, HCO(3) (-) absorption diminished by a fixed amount over a range of initial HCO(3) (-) concentrations of 15 to 80 mM. This change was not caused by alterations in transmural PD or direction of water movement. Because the rate of HCO(3) (-) absorption decreased as the luminal HCO(3) (-) concentration lessened, Na(+)-dependent HCO(3) (-) absorption accounted for an increasing percent of total absorption as the luminal concentration of HCO(3) (-) diminished. The effect of Na(+) on HCO(3) (-) absorption is mediated, at least in part, by H(+) secretion, because luminal CO(2) production (manifested by luminal P(CO2)) dimished as HCO(3) (-) absorption decreased. The changes in P(CO2) are caused by reaction of H(+) with HCO(3) (-) in the luminal fluid because luminal P(CO2) is augmented by the presence of HCO(3) (-) and is diminished by addition of phosphate or Tris buffer. Whether all H(+) secretion requires luminal Na(+) cannot be determined with these experimental techniques because mucosal permeability to Na(+) and the unstirred layer make it impossible to eliminate Na(+) ions from the luminal cell surface. The nature of the mechanism for HCO(3) (-) transport that is not sodium dependent remains to be determined.

Bicarbonates↗
PubMed1977

Quantitation of countercurrent exchange during passive absorption from the dog small intestine: evidence for marked species differences in the efficiency of exchange.

The present investigation was designed to quantitatively assess the possible influence of countercurrent exchange on passive absorption from the small intestine of the dog. Villus blood flow was measured with a modification of the microsphere method. Simultaneously, the absorption from the gut lumen of five diffusible gases (H2, He, CH4, 133Xe, and CO) was determined. Villus blood flow averaged 0.247 +/- 0.03 (SEM) ml/min per g. The observed absorption of H2, He, CH4, and 133Xe was only 16.2 +/- 1.8, 12.8 +/- 2.3, 12.0 +/- 1.8, and 15.8 +/- 1.4 %, respectively, of what this villus blood flow could carry away if it reached perfect equilibrium with the luminal gases. This low absorption rate could result from diffusion limitation to absorption or countercurrent exchange. The diffusive permeability of the barrier seperating the luminal gases and villus blood flow was assessed by measuring the absorption rate of CO. Because absorbed CO binds tightly to hemoglobin, it cannot exchange, and when present in low concentrations its uptake is entirely diffusion limited. Knowledge of the diffusion rate through tissue of the unbound gases relative to that of CO made it possible to calculate the degree to which each of the unbound gases should equilibrate with villus tip blood. The percentage equilibration between lumen and blood at the villus tip for H2, He, CH4, and 133Xe was 99.7, 99.9, 75.6, and 36.0% , respectively. Each of these values greatly exceeded the percentage equilibration of blood leaving the villus (calculated from the observed absorption rate and villus blood flow) and indicated an exchange of 83.8, 87.2, 84.1, and 56.1% of initially absorbed H2, He, CH4, and 133Xe. This result is in accord with theoretical calculations which suggest that countercurrent exchange should be exceedingly efficient in the dog. The striking effect of countercurrent exchange on passive absorption in the dog differs from our previous studies in the rabbit where no exchange was demonstrated. This marked species difference may result from anatomical differences in villus architecture. The dog has long, densely packed villi while the rabbit has broad, widely spaced villi. In the dog, only the villus tips may equilibrate with the lumen, hence a countercurrent gradient may be established in the villus. The entire villus of the rabbit may equilibrate with the lumen and no gradient for countercurrent exchange can therefore be established.

Animals↗
PubMed1981

Interactions between angiotensin peptides and the sympathetic nervous system mediating intestinal sodium and water absorption in the rat.

The purpose of this study was to determine the locus of interaction of angiotensin peptides with the sympathetic nervous system leading to alterations in jejunal sodium and water transport. At low physiological doses, angiotensin II (AII) stimulates jejunal sodium and water absorption, while at high doses peptide inhibits absorption and/or stimulates secretion. Both the stimulation of jejunal transport and the inhibition of absorption were expressed in adrenalectomized rats. However, the stimulation of jejunal water absorption was abolished and a potentiated inhibition of transport was expressed in peripherally sympathectomized rats (intact adrenal medulla) and in normal rats after administration of guanethadine, phentolamine, and prazosin. The angiotensin analog (Sar1 Leu8)-AII has low efficacy and is a potent competitive antagonist of the parent peptide in pressor and myotropic systems, but is a full agonist with even greater potency than AII in stimulating jejunal transport. The increased water transport in response to (Sar1 Leu8)-AII is not secondary to enhanced renal renin release, as the analog also stimulated jejunal transport in the presence of captopril and after bilateral nephrectomy. The stimulation of absorption in response to (Sar1 Leu8)-AII alone or together with AII was abolished by phentolamine. These data demonstrate that AII-increased intestinal absorption is secondary to the release of norepinephrine from nerve endings in the jejunum and that AII inhibition of absorption is not mediated by the sympathetic nervous system. The analog (Sar1 Leu8)-AII is a full agonist in the stimulation of jejunal transport (increased norepinephrine release), but antagonizes the inhibitory response to high doses of AII. Angiotensin peptides are potent modulators of intestinal sodium and water absorption.

Adrenalectomy↗
PubMed1999

Compartmentalization of extracellular cGMP determines absorptive or secretory responses in the rat jejunum.

We examined potential mechanisms by which angiotensin subtype-2 (AT2) receptor stimulation induces net fluid absorption and serosal guanosine cyclic 3',5'-monophosphate (cGMP) formation in the rat jejunum. L-arginine (L-ARG) given intravenously or interstitially enhanced net fluid absorption and cGMP formation, which were completely blocked by the nitric oxide (NO) synthase inhibitor, N-nitro-L-arginine methylester (L-NAME), but not by the specific AT2 receptor antagonist, PD-123319 (PD). Dietary sodium restriction also increased jejunal interstitial fluid cGMP and fluid absorption. Both could be blocked by PD or L-NAME, suggesting that the effects of sodium restriction occur via ANG II at the AT2 receptor. L-ARG-stimulated fluid absorption was blocked by the soluble guanylyl cyclase inhibitor 1-H-[1,2,4]oxadiazolo[4, 2-alpha]quinoxalin-1-one (ODQ). Cyclic GMP-specific phosphodiesterase in the interstitial space decreased extracellular cGMP content and prevented the absorptive effects of L-ARG. Angiotensin II (ANG II) caused an increase in net Na+ and Cl- ion absorption and 22Na+ unidirectional efflux (absorption) from the jejunal loop. In contrast, intraluminal heat-stable enterotoxin of Escherichia coli (STa) increased loop cGMP and fluid secretion that were not blocked by either L-NAME or ODQ. These findings suggest that ANG II acts at the serosal side via AT2 receptors to stimulate cGMP production via soluble guanylyl cyclase activation and absorption through the generation of NO, but that mucosal STa activation of particulate guanylyl cyclase causes secretion independently of NO, thus demonstrating the opposite effects of cGMP in the mucosal and serosal compartments of the jejunum.

Angiotensin II↗
PubMedDate not supplied

Are plasma citrulline and glutamine biomarkers of intestinal absorptive function in patients with short bowel syndrome?

Sensitive biomarkers for intestinal absorptive function would be clinically useful in short bowel syndrome (SBS). Citrulline (Cit) is a product of the metabolism of glutamine (Gln) and derived amino acids by enterocytes. Cit is produced almost exclusively by the gut, which is also a major site of Gln metabolism. The goals of this study were to examine whether plasma Cit and Gln concentrations are biomarkers of residual small intestinal length and nutrient absorptive functions in adult SBS patients followed prospectively. We studied 24 stable adults with severe SBS receiving chronic parenteral nutrition (PN) in a double-blind, randomized trial of individualized dietary modification +/- recombinant human growth hormone (GH). During a baseline week, intestinal absorption studies (% absorption of fluid, kcal, nitrogen, fat, carbohydrate, sodium, phosphorus, and magnesium) were performed and concomitant plasma Cit and Gln concentrations determined. Individualized dietary modification and treatment with subcutaneous injection of placebo (n = 9) or GH (0.1 mg/kg daily x 21 days, then 3 times/week; n = 15) were then begun. PN weaning was initiated after week 4 and continued as tolerated for 24 weeks. Repeat plasma amino acid determination and nutrient absorption studies were performed at weeks 4 and 12. Residual small bowel length at baseline was positively correlated with baseline plasma Cit (r = 0.467; p = .028). However, no significant correlations between absolute Cit or Gln concentrations and the percent absorption of nutrient substrates at any time point were observed. Similarly, no correlation between the change in Cit or GLN concentration and the change in % nutrient absorption was observed (baseline vs weeks 4 and 12, respectively). By weeks 12 and 24, 7 and 13 subjects were weaned completely from PN, respectively. However, baseline plasma Cit or Gln did not predict PN weaning at these time points. We concluded that plasma Cit (but not Gln) concentrations appeared to be an indicator of small intestinal length in adult SBS. However, neither plasma Cit nor Gln was a biomarker for intestinal absorptive function in this cohort of patients with SBS.

Biomarkers↗
PubMed1997

Kinetic analysis of the intestinal iron absorption process in situ. The potential of vascularly autoperfused intestinal loops.

1 Blood sampling from mesenteric venules during absorption in situ is a useful tool to analyse intestinal absorption kinetics and prehepatic metabolism in different sections of the rat small intestine. By use of a micromanipulator, the method can be applied to the duodenum. This part of the small intestine shows the strongest adaptation of non-haem iron absorption to the demand for iron. 2 Iron absorption kinetics was linear in duodenal and jejunal segments. In iron-deficient animals, intestinal iron absorption capacity was increased in the duodenum, while simultaneously determined galactose absorption showed no change. 3 In situ perfusion and cannulation of mesenteric venules in duodenal segments are described. The use of a micromanipulator permits varying the blood volume collected by changing the vertical angle between the cannula and the mesenteric vessel. 4 Intestinal iron absorption rates remained close to constant when blood flow rates were varied by a factor of about ten. Plasma concentrations of absorbed iron vs mesenteric blood flow rates followed a hyperbolic function, as the plasma concentration of absorbed iron in mesenteric venules increased to the same extent as the blood flow decreased. 5 As the plasma transferrin concentration did not change over the experimental period, the concentration of absorbed iron in the mesenteric plasma exceeded the iron-binding capacity of plasma transferrin at low blood flow rates. This observation shows that enhancement of intestinal iron absorption does not require a corresponding increase in plasma iron-binding capacity in the intestinal tissue. 6 Vascularly perfused gut loops were also used to measure prehepatic metabolism, which may influence organotropism of carcinogenic metabolites. Therefore, this type of preparation is likely to find a variety of toxicological applications.

Animals↗
PubMed2005

The advantages of the Ussing chamber in drug absorption studies.

By adding high concentrations of test drugs to an Ussing chamber with rat jejunum, we established a system that yields very high correlations between the rat absorption percentage and the membrane permeability, and that can accurately predict the absorption percentage for rats. An advantage of this technique is that, unlike the results obtained using Caco-2, the slope of the absorption/membrane-permeability curve is gentle, which facilitates a more exact prediction of the absorption percentage. In addition, the results obtained with this technique demonstrated that it could be used to evaluate the absorption percentage of drugs with an affinity for P-glycoprotein (P-gp), which cannot be assessed using Caco-2. This method also allows for cassette screening, which would facilitate evaluation of the contribution of P-gp to absorption in the small intestine. Cassette screening showed that absorption of fexofenadine was unaffected by combination with the P-gp substrate ketoconazole. Consistent with this finding, in vivo studies showed that ketoconazole did not affect the Fa Fg for fexofenadine, a pharmacokinetic parameter that reflects absorption and bioavailability in the small intestine. This confirms the usefulness of the Ussing chamber for cassette screening and also suggests that intestinal P-gp has a minimal contribution to drug absorption.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Dermal absorption and tissue disposition of 3,3',4, 4'-tetrachlorobiphenyl (TCB) in an ex-vivo pig model: assessing the impact of dermal exposure variables.

TCB is one of the dioxin-like polychlorinated biphenyls (PCBs). This research was designed to help assess the risk of occupational and environmental TCB exposure. To evaluate exposure variables' effects on dermal absorption and cutaneous disposition, 14C-TCB (40 microg/cm(2)) in acetone, methylene chloride, a water-acetone mixture, and a soil-based mixture were applied in an ex-vivo pig-skin-flap model (n = 4-5/treatment). Dermal absorption (0.11-0.66%, 8 hr) and penetration (1.14-2.48%) varied according to exposure conditions. Acetone and methylene chloride vehicles differed in absorption profiles and skin penetration patterns but were similar in absorption amounts. Adding water to the acetone did not change absorption but did alter the penetration pattern. The non-occluded soil-based mixture showed more absorption than did the liquid vehicles (p<0.05), but occlusion significantly (p<0.05) decreased that absorption (0.66-->0.29%, 8 hr) and penetration (2.48-->1.11%). In conclusion, dermal absorption data from liquid-organic or aqueousorganic mixtures may underestimate the risk of exposure to TCB-contaminated soil.

Animals↗
PubMed2004

Cholesterol absorption is mainly regulated by the jejunal and ileal ATP-binding cassette sterol efflux transporters Abcg5 and Abcg8 in mice.

In the present study, we investigated whether intestinal sterol efflux transporters Abcg5 and Abcg8 play a major role in determining variations in cholesterol (Ch) absorption efficiency, and we compared the physiological functions of the duodenal, jejunal, and ileal Abcg5 and Abcg8 on the absorption of Ch and sitostanol in inbred mice challenged with various amounts of Ch, sitostanol, hydrophilic, or hydrophobic bile acids. We found that Abcg5 and Abcg8 in the jejunum and ileum, but not in the duodenum, were main factors in determining, in part, variations in Ch absorption efficiency. The jejunal and ileal Abcg5 and Abcg8 played a major regulatory role in response to high dietary cholesterol and were more sensitive in the regulation of Ch absorption when compared with sitostanol absorption. These results, combined with different sterol uptake rates, suggest that the absorption efficiency of Ch and sitostanol is determined by the net results between influx and efflux of intraluminal Ch and sitostanol molecules crossing the apical membrane of the enterocyte. Hydrophilic and hydrophobic bile acids influenced Ch absorption through mediating Ch solubilization and its physical-chemical state within the small intestinal lumen. We conclude that Ch absorption is mainly regulated by the jejunal and ileal Abcg5 and Abcg8 in mice.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed1983

Disaccharide feedings enhance rat jejunal macromolecular absorption.

Disaccharide feedings to post-weaning rats alters their jejunal barrier to macromolecular absorption. Penetration of horseradish peroxidase (HRP) across the jejunum was enhanced after short-term high concentration gavage (30 g . kg-1 . day-1) of lactose that produces weight loss, osmotic diarrhea, and jejunal mucosal damage. HRP absorption was also increased by longer term feedings of lower levels of disaccharide that did not produce body weight alterations, diarrhea, or cell damage. Rats without diarrhea and gavaged with 7.5 g . kg-1 . day-1 of either lactose or maltose showed an increase in lumen to blood HRP absorption after 21 days of feedings. Also, lactose or maltose in the solid food diet at 30 g . kg-1 . day-1 for 21 days did not lead to diarrhea but produced an increase in jejunal lumen to blood HRP absorption. Rats having no diarrhea and receiving 15 g . kg-1 . day-1 of lactose or maltose in the drinking water for 21 days, showed an increase in jejunal HRP absorption. When rats were fed either lactose or maltose for 21 days glucose absorption became totally dependent upon the sugar concentration in the perfusion medium. The kinetics of this glucose absorption are compatible with a decrease in the "unstirred" layer. Disaccharide-induced HRP absorption may be mediated by transport from endocytotic vesicles across the jejunal epithelium.

Animals↗
PubMed1990

Development of the neonatal rat small intestinal barrier to nonspecific macromolecular absorption: effect of early weaning to artificial diets.

We studied the effect of early weaning from maternal breast milk to artificial diets on rat jejunal absorption of an exogenous 40-kD glycoprotein, horseradish peroxidase (HRP). Rat pups, fed maternal milk (MM) from birth, received one of three diets for the last 4 d before weaning (d 17-21): MM, protein hydrolysate formula (PH), or soy formula (S). Some rats were pretreated on d 14 with intraperitoneal hydrocortisone (5 mg/rat). In MM-fed rat pups, jejunal HRP absorption was markedly higher on d 17 than on d 21. [Geometric means (95% confidence interval) were: d 17, 626.4 (461.3, 850.6) versus d 21, 90.6 (48.2, 170.5) IU HRP/mL x cm x min, p less than 0.01.] By contrast, 21-d-old PH- and S-fed pups maintained elevated absorption of the tracer [PH, 292.3 (177.5, 480.6), p less than 0.05 versus MM pups, S, 340.8 (164.4, 704.8), p less than 0.01 versus MM pups]. Wt-matched control studies indicate that the difference in HRP absorption was not due to the smaller body wt of formula-fed pups. The increased absorption in formula-fed animals was suppressed by hydrocortisone. In S-fed pups, the increased macromolecular absorption appeared, in part, to be the result of diffusion across altered villus absorptive cells. In PH-fed pups, there was no evidence of damage and HRP absorption appeared to occur by vesicle-mediated transport. Delay in the normal maturation of small intestinal "closure" appears to be associated with early weaning to artificial diets. This may lead to increased nonspecific macromolecular permeability that could result in immune-mediated sensitization and food intolerance.

Age Factors↗
PubMed1998

The influence of meat on nonheme iron absorption in infants.

During weaning the infant has a high iron requirement, and highly available dietary iron is needed to ensure optimal iron status. Muscle tissue has been identified as an enhancer of nonheme iron absorption in adults, although the influence of meat on nonheme iron absorption in infants has not been previously reported. The effect of the addition of 25 g of meat (lean beef) on nonheme iron absorption from a home-prepared vegetable purée meal (80 g of vegetables) was investigated in infants in the present study. The meals did not differ in their contents of other known enhancers or inhibitors of nonheme iron absorption. Incorporation of stable isotopes of iron (57Fe and 58Fe) into red blood cells 14 d after intake was used to measure iron absorption, using a cross-over design in eight healthy infants 43-49 wk of age. Nonheme iron absorption was significantly increased (p = 0.002) from the vegetable purée with added meat (geometric mean 15.0%) compared with the puréed vegetables (geometric mean 9.9%). These results thus suggest that meat is also an enhancer of nonheme iron absorption in infants and that nonheme iron absorption from weaning foods can be increased by the addition of meat.

Adult↗
PubMed1992

Sites and patterns of absorption of 3,5,3'-triiodothyronine and thyroxine along rat small and large intestines.

It is clear that some thyroid hormone is absorbed from mammalian intestines, but numerous aspects of this process remain unresolved, including elucidation of the locations, extent and mechanisms of absorption, and the role of absorption in thyroid hormone economy. Our goal was to identify the sites and patterns and estimate rates of absorption of both tracer T4* and T3* comprehensively along the entire length of rat intestines, with normal contents included, to gain further insight into the role of this organ in whole-body thyroid hormone regulation. We measured absorption directly in situ in fed rats, using a variant of the classic intestinal loop technique used by others demonstrating absorption of T4 or of T3 from portions of rat intestines under various conditions. Rats were anesthetized, bile ducts were ligated, and absorption was measured from pylorus to anus, in 14 loops of intestines previously injected with T3* or with T4*, or with T3* and T4* injected in adjacent loops. Rats were maintained under otherwise approximately normal conditions, with intestines in situ and abdomen closed, until killing at 2 h. Excised loop radioactivity was measured and loops were homogenized, extracted, and chromatographed quantitatively to evaluate remaining and absorbed T3* and T4*. Absorption of both T3* and T4* were clearly present and were approximately uniform from all small and large intestinal sections, all containing normal intestinal contents, indicating that the entire organ is involved in whole-body thyroid hormone regulation. Furthermore, T3* and T4* were absorbed at approximately the same rate, adding to evidence reported by others for a simple diffusion absorption mechanism.

Animals↗