Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Absorption”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,099 records · Page 61Linked to original sources
PubMed1971

Intestinal transport of dipeptides in man: relative importance of hydrolysis and intact absorption.

A 30 cm segment of the duodenum, jejunum, or ileum of normal human volunteers was perfused, on separate occasions, with test solutions containing either glycylglycine, free glycine, glycylleucine, or equimolar amounts of free glycine and free leucine. Luminal fluid contained no hydrolytic activity against glycylglycine and minimal activity against glycylleucine. In each intestinal segment, amino acid absorption rates were significantly greater from the test solutions containing the same amount of amino acids in dipeptide than in free form(as high as 185% increase). Perfusion of each intestinal segment with a test solution containing the equimolar mixture of free glycine and free leucine always resulted in a greater leucine than glycine absorption rate. This preferential absorption of leucine, however, was either diminished (jejunum) or almost abolished (duodenum and ileum) when the glycylleucine solution instead of the equimolar mixture was presented to the intestinal mucosa. Among the three segments, the duodenum exhibited the least potential for the disappearance of dipeptides. The jejunal and ileal dipeptide disappearance rates were either similar for glycylleucine (94% vs. 92%) or slightly different for glycylglycine (92% vs. 79%). Despite lack of a remarkable difference in the disappearance rates, absorption rates of constituent amino acids were markedly greater in the jejunum than in the ileum. This reduced amino acid absorption was brought about by a greater accumulation of free amino acids in the lumen of the ileal segment (3 to 10-fold difference). Inhibition of free glycine absorption by leucine during the perfusion of the intestine with a test solution containing glycylglycine and leucine did not result in any greater concentration of free glycine in the lumen than when the glycylglycine test solution did not contain free leucine. Similarly, inhibition of free glycine and free leucine absorption by isoleucine was not accompanied by any remarkable alteration of absorption rates of the constituent amino acids of glycylleucine. The results of these studies suggest that: (a) dipeptide disappearance in the gut lumen is principally accomplished by intact absorption and not by hydrolysis; (b) intracellular hydrolysis of dipeptides is markedly greater in the ileum than in the jejunum, while dipeptide absorption rates are either similar or only slightly different in these two segments; (c) there is no appreciable hydrolysis of glycylglycine by the membrane-bound enzymes and only a small fraction of glycylleucine is hydrolyzed by these enzymes.

Adolescent↗
PubMed1975

Stimulation of active and passive sodium absorption by sugars in the human jejunum.

The effects of glucose and fructose on water and sodium absorption in the human jejunum were compared to assess the relative contribution of active and passive sugar stimulation of sodium transport. The effect of fructose is assumed to be entirely passive, and the difference between the effects of fructose and glucose is assumed to be a measure of sugar-stimulated, active sodium absorption. Water and sodium movement with mannitol was the base line. Three sets of test solutions with differing sugar concentrations were studied. Fructose stimulated 66-100 per cent as much net sodium and water absorption as glucose. Fructose stimulated potassium absorption, whereas glucose stimulated potassium secretion. Urea absorption was stimulated by both sugars. Glucose and fructose stimulated sodium absorption when chloride was the major anion, but they had relatively little effect on net sodium movement when chloride was replaced by bicarbonate or sulfate. It is concluded that glucose stimulates passive and active sodium transport in the human jejunum. Stimulated active sodium absorption generates an electrical potential across the mucosa that causes sodium (and potassium) secretion and partly or completely nullifies the effect of active sodium transport on net sodium movement. Net sodium absorption sitmulated by glucose is mainly (66-100 per cent) the passive consequence of solvent flow. The accompanying anion determines the degree to which sugars stimulate sodium absorption (C1 greater than SO-4 greater than HCO3). The effects of bicarbonate and sugars on jejunal sodium absorption are not additive.

Anions↗
PubMed1977

Role of 1,25-dihydroxyvitamin D3 on intestinal phosphate absorption in rats with a normal vitamin D supply.

In vitamin D-deficient rats, impaired intestinal phosphorus (P) absorption can be corrected by 1,25-dihydroxyvitamin D(3)[1,25-(OH)(2)D(3)]. In the present study, it was investigated whether changes in 1,25-(OH)(2)D(3) production can influence intestinal P transport also in animals with a normal supply of vitamin D. The intestinal P absorption was evaluated in rats using both the in situ duodenal loop technique and the determination of the overall gastrointestinal absorption under three conditions known to influence the production of 1,25-(OH)(2)D(3): (a) variation in dietary P, (b) thyroparathyroidectomy (TPTX) with or without administration of parathyroid hormone (PTH), and (c) treatment with disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP). In all circumstances changes in duodenal absorption paralleled the changes in the overall fractional absorption. (a) Lowering dietary P stimulated P absorption. (b) TPTX decreased P absorption. This effect was corrected either by the administration of PTH or by the administration of 1,25-(OH)(2)D(3). (c) EHDP, when given at a dose known to inhibit 1,25-(OH)(2)D(3) formation, decreased the duodenal P absorption in both intact and TPTX animals. This effect was corrected by 1,25-(OH)(2)D(3). In the TPTX-EHDP-treated animals, the administration of PTH did not rectify the low duodenal P absorption. These results support the thesis that, in rats with normal vitamin D supply, variations in the endogenous production of 1,25-(OH)(2)D(3) change the rate of P absorption. However, these changes are in such magnitude that they are of relatively small importance when compared to the effect of variation in the dietary intake of P. These results also strongly suggest that the action of PTH on duodenal P transport is mediated by its effect on 1,25-(OH)(2)D(3) production, inasmuch as the effect of the hormone is abolished after blocking the renal 1-hydroxylation with EHDP.

Animals↗
PubMed1988

Role of vitamin D-dependent and vitamin D-independent mechanisms in absorption of food calcium.

We measured net calcium absorption and the calcium content of the digestive glands secretions in people with widely different serum concentrations of 1,25 dihydroxy vitamin D (hereafter referred to a 1,25-D). Patients with end stage renal disease on hemodialysis served as a model of human 1,25-D deficiency; they were also studied when they had abnormally high serum 1,25-D concentrations as a result of short periods of treatment with exogenous 1,25-D. Normal subjects were studied for comparison. The amount of calcium secreted into the duodenum by the digestive glands was found to be trivial compared to the calcium content of normal or even low calcium meals; therefore, values for net and true net calcium absorption differed only slightly. There was a linear correlation between true net calcium absorption and serum 1,25-D concentration. By extrapolating the short distance to a zero value for serum 1,25-D, D-independent true net calcium absorption was estimated. By subtracting D independent from true net calcium absorption, values for D-dependent absorption were obtained. For a given level of meal calcium intake, D-dependent calcium absorption was found to be directly proportional to serum 1,25-D concentration. At any given value for serum 1,25-D, absorption via the D-dependent mechanism was approximately the same with a low (120 mg) calcium meal as it was when meal calcium intake was increased to 300 mg. We interpret this to mean that the D-dependent mechanism is saturated or nearly saturated by low calcium meals. The D-independent absorption/secretion mechanism resulted in secretion (a loss of body calcium in the feces) when intake was low (120 mg per meal) and absorption when intake was normal. All of the increment in calcium absorption that occurs when low or normal calcium meals are supplemented with extra calcium is mediated by the D-independent mechanism.

Adult↗
PubMed1991

Intestinal absorption of magnesium from food and supplements.

The purpose of this study was to measure magnesium absorption over the wide range of intakes to which the intestine may be exposed from food and/or magnesium-containing medications. Net magnesium absorption was measured in normal subjects after they ingested a standard meal supplemented with 0, 10, 20, 40, and 80 mEq of magnesium acetate. Although absorption increased with each increment in intake, fractional magnesium absorption fell progressively (from 65% at the lowest to 11% at the highest intake) so that absorption as a function of intake was curvilinear. This absorption-intake relationship was almost perfectly represented by an equation containing a hyperbolic function plus a linear function. Our results are statistically compatible with a magnesium absorption process that simultaneously uses a mechanism that reaches an absorptive maximum, plus a mechanism that endlessly absorbs a defined fraction (7%) of ingested magnesium. Compared to previous studies of calcium absorption, much less magnesium that calcium was absorbed at intakes above 8 mEq/meal, apparently due to greater restriction of intestinal permeability to magnesium. We also found that magnesium from a high magnesium-containing food source, almonds, was just as bioavailable as from soluble magnesium acetate. In contrast, magnesium absorption from commercially available enteric-coated magnesium chloride was much less than from magnesium acetate, suggesting that enteric coating can impair magnesium bioavailability.

Adult↗
PubMed1995

The effect of surgical bowel manipulation and anesthesia on intestinal glucose absorption in rats.

The effects of surgical bowel manipulation and anesthesia on intestinal glucose absorption were determined in chronically catheterized rats. Total and passive rates of glucose absorption were measured using 3-O-methyl-glucose (3OMG) and L-glucose, metabolically inert analogues of D-glucose. The rates of 3OMG absorption immediately postoperative and 4 h later were 86 and 62% less than the absorption rate 6 d postoperative. The absorption rates of 3OMG 1 and 2 d postoperative were not different from 6 d postoperative. Absorption of L-glucose was not altered by bowel manipulation and anesthesia. Even after correction for the increased resistance of the unstirred water layer (UWL) after bowel manipulation, the rates of total and active intestinal glucose absorption immediately postoperative were only 11 and 15% of predicted rates of absorption. In chronically catheterized rats, > 75% of luminal 3OMG at a concentration of 400 mM was absorbed by active transport. The Km and Vmax of 3OMG active transport corrected for the resistance of the UWL were 11.3 mM and 15.6 mumoles/min, respectively. We conclude that measurements of intestinal glucose absorption performed within 24 h of surgical bowel manipulation greatly underestimate active absorption even if corrections are made to account for the increased resistance of the UWL.

3-O-Methylglucose↗
PubMed2005

Soft tissue absorption tomography with correction for scattering aberrations.

Among the many factors involved in ultrasound attenuation phenomena, scattering effects play a major role, even in the unexpected case of soft tissues. It is proposed in this study to quantitatively evaluate the scattering affecting the measurements before reconstructing the absorption parameter alone. The reconstruction procedure involves three steps: (1) Estimating the sound speed map using a transmission tomography algorithm. This estimation procedure provides a numerical phantom of the organ probed, cleared of all dissipative components. This absorption free phantom mimics the (viscoacoustic) tissues imaged except for the density and absorption characteristics: the density a priori equals 1000 kg/m3 and the absorption is not taken into account. The impedance fluctuations in the object are therefore approximated on the basis of the sound speed contrast. (2) Synthesing the field scattered by the absorption free phantom; the attenuation observed here results solely from the scattering phenomenon. The synthesis is carried out using a finite-element time domain code simulating the ultrasonic propagation through the phantom. It provides the scattering distortion reference introduced into the log spectral absorption estimator. (3) Reducing the scattering distortions affecting the integrated absorption measured along the ray paths using a log spectral procedure. The corrected integrated absorption is then processed using a tomographic reconstruction procedure that provides an estimate of the absorption distribution. Simple numerical simulations show the improvement obtained in the absorption estimates with this approach.

Absorption↗
PubMed1985

Effect of long term treatment with calcitriol on calcium absorption and mineral metabolism in postmenopausal osteoporosis.

The mechanism of impaired calcium absorption in postmenopausal osteoporosis is controversial. If it is caused by calcitriol deficiency, it should be corrected by long term administration of physiological doses of this metabolite, whereas if it is caused by either a primary defect in calcium absorption or intestinal resistance to calcitriol action, it should not be. In 56 osteoporotic women, mean (+/- SE) fractional calcium absorption (0.52 +/- 0.02) was lower (P less than 0.001) than that in 20 age-matched normal women (0.61 +/- 0.02). Treatment with calcitriol (0.5-0.75 micrograms/day) increased calcium absorption after 6-12 months to 0.67 +/- 0.02 (P less than 0.001) and, in 29 patients, to 0.66 +/- 0.02 (P less than 0.001) after 24 months. After treatment, only 1 patient still had subnormal calcium absorption. In 26 patients treated with placebo for 6-12 months, there was no significant change in calcium absorption. For all studies, total calcium absorption (fractional absorption X estimated dietary intake) correlated directly with urinary calcium excretion (r = 0.61; P less than 0.001). Urinary hydroxyproline excretion, an index of bone resorption, was 31.0 +/- 1.5 mg/dl glomerular filtration rate (GFR) initially and decreased during treatment to 24.6 +/- 1.1 mg/dl GFR (P less than 0.001) after 6-12 months and to 27.9 +/- 1.3 mg/dl GFR (P less than 0.01) after 24 months. The finding that calcium absorption can be normalized by small doses of calcitriol supports the hypothesis that insufficient endogenous production of calcitriol is the major cause of decreased calcium absorption in postmenopausal osteoporosis.

Aged↗
PubMed1998

Dose dependency in the gastrointestinal absorption of cefatrizine: correlation between in vivo and in situ.

We evaluated the dose-dependent (saturable) gastrointestinal absorption of cefatrizine, an aminocephalosporin transported by peptide carriers, in rats by a physiological mechanism-based approach to clarify its absorption characteristics and to examine the in vitro (in situ)-in vivo correlation in intestinal transport. With an increase in oral dose (mumol/5 ml/kg) from 5 (low) to 50 (high), the intestinal absorption rate constant (ka), which was estimated by analysis of gastrointestinal disposition, decreased markedly, from 0.301 to 0.056 min-1. This decrease was ascribable to the saturability of intestinal membrane transport, of which the concentration dependency in the perfused intestine was similar in extent to the dose dependency in ka. However, the apparent absorption rate constant (ka'), which was estimated by analysis of plasma concentrations after oral administration, decreased only modestly from 0.037 to 0.023 min-1. This was associated with the result that, at the low dose, ka' was far smaller than ka and comparable with k(g) (gastric emptying rate constant), suggesting gastric emptying-limited absorption. At the high dose, where intestinal cefatrizine absorption was less efficient, ka' was closer to ka than k(g). It was also observed that the bioavailability was close to unity, independent of dose, suggesting that the intestinal transit time is long enough to achieve complete absorption, even at the high dose, where intestinal cefatrizine absorption is less efficient. Thus, it was found that the effect of saturability in the intestinal transport of cefatrizine is apparently attenuated in its overall gastrointestinal absorption because of the involvement of gastric emptying and intestinal transit time as additional physiological factors to define absorption. It was also found that a scaling factor is required to correlate the intestinal membrane transport between in vitro (in situ) and in vivo, though this remains to be verified to be utilized for developing oral drug delivery strategies and optimizing oral drug therapy.

Administration, Oral↗
PubMed1997

Association between intestinal vitamin D receptor, calcium absorption, and serum 1,25 dihydroxyvitamin D in normal young and elderly women.

The exact mechanism for the decrease in intestinal calcium absorption with age is not yet understood. A decrease with age in serum 1,25-dihydroxyvitamin D (1,25(OH)2D) or a decrease in the intestinal vitamin D receptor (VDR) protein concentration are possible causes. The objective of this study was to examine the effect of age on these factors. Fifty-nine young women age 25-35 years were compared with 41 elderly women age 65-83 years who underwent measurements of VDR, calcium absorption using a 20 mg and 100 mg calcium carrier, and calciotropic hormones. Calcium absorption by both tests was lower in the elderly women compared with the young women (p < 0.05). Serum 1,25(OH)2D and duodenal VDR protein concentration were not significantly different between the two age groups. Serum 1,25(OH)2D correlated with the 20 mg calcium absorption test in both young (r = 0.35, p < 0.007) and elderly women (r = 0.58, p < 0.0001) and with the 100 mg calcium absorption in the elderly (r = 0.32; p < 0.05). VDR did not correlate with calcium absorption in young women or elderly women, nor did VDR correlate with serum 1,25(OH)2D and serum 25-hydroxyvitamin D. In summary, the decrease in calcium absorption cannot be explained by a decrease in intestinal VDR. The correlation between serum 1,25(OH)2D and both calcium absorption tests only accounts for 12-30% of the variance in the age-related change in the calcium absorption tests. Other factors, not yet understood, are responsible for the decline in calcium absorption with age.

Adult↗
PubMed1992

Percutaneous absorption of drugs.

The skin is an evolutionary masterpiece of living tissue which is the final control unit for determining the local and systemic availability of any drug which must pass into and through it. In vivo in humans, many factors will affect the absorption of drugs. These include individual biological variation and may be influenced by race. The skin site of the body will also influence percutaneous absorption. Generally, those body parts exposed to the open environment (and to cosmetics, drugs and hazardous toxic substances) are most affected. Treating patients may involve single daily drug treatment or multiple daily administration. Finally, the body will be washed (normal daily process or when there is concern about skin decontamination) and this will influence percutaneous absorption. The vehicle of a drug will affect release of drug to skin. On skin, the interrelationships of this form of administration involve drug concentration, surface area exposed, frequency and time of exposure. These interrelationships determine percutaneous absorption. Accounting for all the drug administered is desirable in controlled studies. The bioavailability of the drug then is assessed in relationship to its efficacy and toxicity in drug development. There are methods, both quantitative and qualitative, in vitro and in vivo, for studying percutaneous absorption of drugs. Animal models are substituted for humans to determine percutaneous absorption. Each of these methods thus becomes a factor in determining percutaneous absorption because they predict absorption in humans. The relevance of these predictions to humans in vivo is of intense research interest. The most relevant determination of percutaneous absorption of a drug in humans is when the drug in its approved formulation is applied in vivo to humans in the intended clinical situation. Deviation from this scenario involves the introduction of variables which may alter percutaneous absorption.

Animals↗
PubMed2001

Assessing the absorption of new pharmaceuticals.

The advent of more efficient methods to synthesize and screen new chemical compounds is increasing the number of chemical leads identified in the drug discovery phase. Compounds with good biological activity may fail to become drugs due to insufficient oral absorption. Selection of drug development candidates with adequate absorption characteristics should increase the probability of success in the development phase. To assess the absorption potential of new chemical entities numerous in vitro and in vivo model systems have been used. Many laboratories rely on cell culture models of intestinal permeability such as, Caco-2, HT-29 and MDCK. To attempt to increase the throughput of permeability measurements, several physicochemical methods such as, immobilized artificial membrane (IAM) columns and parallel artificial membrane permeation assay (PAMPA) have been used. More recently, much attention has been given to the development of computational methods to predict drug absorption. However, it is clear that no single method will sufficient for studying drug absorption, but most likely a combination of systems will be needed. Higher throughput, less reliable methods could be used to discover 'loser' compounds, whereas lower throughput, more accurate methods could be used to optimize the absorption properties of lead compounds. Finally, accurate methods are needed to understand absorption mechanisms (efflux-limited absorption, carrier-mediated, intestinal metabolism) that may limit intestinal drug absorption. This information could be extremely valuable to medicinal chemists in the selection of favorable chemo-types. This review describes different techniques used for evaluating drug absorption and indicates their advantages and disadvantages.

Animals↗
PubMed1994

Absorption activity and barrier properties in the endolymphatic sac. Ultrastructural and morphometric analysis.

A constant volume of horseradish peroxidase (HRP) was injected directly into the endolymphatic sac (ES) lumen of the guinea pig to investigate the detailed absorption activity and the barrier properties of the ES. The reaction products were analyzed using an ultrastructural and morphometric method 1 to 10 h after the injection of this tracer. The epithelial cells in the proximal portion did not absorb the intraluminal HRP at any intervals after the tracer injection. The epithelial cells of the intermediate portion were classified clearly into two types according to their absorption activity: active-absorptive, and non-active cells. Uptake in the active-absorptive cells reached its maximal rate 8 h after the injection and then decreased. The active-absorptive cells in teh intermediate portion are considered to play a major role in the macromolecular absorption in the ES epithelium. The non-active cells scarcely absorbed the intraluminal HRP, suggesting that these cells are not involved in the macromolecular absorption. The absorption activity in the distal portion was lower than that in the active-absorptive cells in the intermediate portion 1 to 8 h after the HRP injection, while higher 10 h after the injection. Not only the intermediate portion but also the distal portion may play an active role in the macromolecular absorption. In no portion of the ES did intraluminal HRP penetrate beyond the junctional complexes between epithelial cells or through the cytoplasm. It is conceivable that there is a tight barrier to the intraluminal macromolecules in the epithelial linings of the ES.

Absorption↗
PubMed1997

Gastrointestinal absorption of metals.

Estimating gastrointestinal absorption remains a significant challenge in the risk assessment of metals. This presentation reviews our current understanding of the gastrointestinal absorption of lead (Pb) to illustrate physiological mechanisms involved in metal absorption, new approaches that are being applied to the problem of estimating metal absorption in humans, and issues related to integrating this information into risk assessment. Absorption of metals can be highly variable in human populations because it is influenced by a variety of factors that include the chemical form of the metal, environmental matrix in which the ingested metal is contained, gastrointestinal tract contents, diet, nutritional status, age, and, in some cases, genotype. Thus, in risk assessment models, gastrointestinal absorption is best described as a variable whose distribution is determined in part by the above multiple influences. Although we cannot expect to evaluate empirically each of the above factors in human populations, we can expect to achieve a sufficiently detailed understanding of absorption mechanisms to develop conceptual and, eventually, quantitative models of absorption that account for some aspects of individual variability. A conceptual model is presented of the physiological processes involved in the transfer of ingested metals from the lumen of the gastrointestinal tract to the blood circulation. Components of the model include delivery of the metal to the site(s) of absorption; distribution of metal among intracellular and extracellular ligands and transcellular and paracellular pathways of transfer across the gastrointestinal tract epithelium. The gastrointestinal absorption of Pb is discussed in the context of this model.

Biological Availability↗
PubMed1998

Gastrointestinal absorption of metals.

Estimating gastrointestinal absorption remains a significant challenge in the risk assessment of metals. This presentation reviews our current understanding of the gastrointestinal absorption of lead (Pb) to illustrate physiological mechanisms involved in metal absorption, new approaches that are being applied to the problem of estimating metal absorption in humans, and issues related to integrating this information into risk assessment. Absorption of metals can be highly variable in human populations because it is influenced by a variety of factors that include the chemical form of the metal, environmental matrix in which the ingested metal is contained, gastrointestinal tract contents, diet, nutritional status, age, and, in some cases, genotype. Thus, in risk assessment models, gastrointestinal absorption is best described as a variable whose distribution is determined in part by the above multiple influences. Although we cannot expect to evaluate empirically each of the above factors in human populations, we can expect to achieve a sufficiently detailed understanding of absorption mechanisms to develop conceptual and, eventually, quantitative models of absorption that account for some aspects of individual variability. A conceptual model is presented of the physiological processes involved in the transfer of ingested metals from the lumen of the gastrointestinal tract to the blood circulation. Components of the model include delivery to the site(s) of absorption; distribution among intracellular and extracellular ligands and transcellular and paracellular pathways of transfer across the gastrointestinal tract epithelium. The gastrointestinal absorption of Pb is discussed in the context of this model.

Animals↗
PubMed1983

Net absorption and ruminal concentrations of metabolites in nonpregnant dry Holstein cows before and after intraruminal acetic acid infusion.

Objectives were to define daily patterns of net absorption of various nutrients and to assess effects of intraruminal infusion of acetic acid on concentrations of ruminal fluid and net absorption of various metabolites. These characteristics were measured in three nonpregnant, dry Holstein cows (491 kg) at hourly intervals for 24 h before and after 5 days of intraruminal infusion of acetic acid to provide energy equal to 10% of daily intake of metabolizable energy. Cows were fed a completely mixed, 60% corn silage, 40% grain supplement diet at maintenance intake; daily rations were split into two feedings. Net rates of absorption were greatest after feeding and least during early morning. Net absorption of all metabolites measured was similar for the two daily feeding intervals, indicating daily net absorption could be calculated from either feeding interval. Intraruminal infusion of acetic acid caused increased ruminal and plasma concentrations of acetate, increased net absorption of acetate, and almost a twofold increased loss of urea-nitrogen from plasma to the gut. Sixty-nine percent of acetic acid infused was accounted for by increased net absorption of acetate. Ruminal fluid concentrations and net absorption of other volatile fatty acids were not affected by infusion of acetic acid. Net absorptions of ammonia-nitrogen, L-lactate, and glucose likewise were not affected. Net absorption of volatile fatty acid and L-lactate was 43% of daily intake of metabolizable energy.

Absorption↗
PubMed1988

The mechanisms of intestinal absorption of the carcinogen MNNG (N-methyl-N'-nitro-N-nitrosoguanidine).

We studied the characteristics and mechanisms of MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) intestinal absorption and the interaction between bile acids and fatty acids and MNNG absorption rate in vivo in male Sprague-Dawley rats. We perfused a segment of the proximal small bowel with a physiological solution containing MNNG to assess its basic kinetics and the influence of some physiological and dietary factors on carcinogen absorption. We found that MNNG was absorbed by simple passive diffusion. Transport of MNNG was the highest at pH 6.0. The addition of the bile salt, taurocholate by itself, greatly increased MNNG absorption, while the addition of the long-chain unsaturated fatty acids, oleic and linoleic, decreased the rate of absorption of MNNG. The phospholipid lecithin addition to the perfusate did not change the rate of MNNG absorption. Induction of dietary vitamin A deficiency (serum vitamin A level decreased from 40.9 to 13.7 micrograms/dl) did not change the absorption rate of MNNG. These studies demonstrate that bile acids, dietary fatty acids, and the pH of the intestinal content can modify the rate of absorption of this carcinogen by the small intestine. Since initial intestinal absorption determines serum levels and subsequent reabsorption and enterohepatic cycling determines long-term lumenal levels, serum levels, and total body content, factors which modify the rate of intestinal absorption of MNNG could also modify its carcinogenicity.

Animals↗
PubMed1991

[Absorption of the urinary constituents from canine ileum].

To clarify the mechanism of metabolic changes after using intestinal segments as a urinary tract, absorption of urinary constituents from the ileum was studied in dogs. An isolated distal ileum (30 cm in length) was anastomosed to the urinary bladder in each dog. Although these animals maintained the normal renal function throughout the experimental period, mild acidosis was noticed one month after anastomosis and it became severe after six months. Stagnation of a urine-like solution (artificial urine: AU) in the isolated ileum resulted in an absorption of 66% of the instilled solvent on average during 60 minutes. The average absorption rates of each AU constituent were as follows: sodium 63%, potassium 80%, chloride 83%, phosphorus 68%, magnesium 34%, urea nitrogen 93% creatinine 56%, and ammonia 97%. On the contrary, calcium increased in the stagnated fluid by 21%. In spite of the severe histologic changes in the villi of the ileal mucosa, which became atrophic and flat, no deterioration in the absorptive capacity of the AU constituents was noticed during the six month experimental period. Furosemide administration suppressed the absorption of urinary constituents, especially water and sodium. On the other hand, the absorption of urea nitrogen and ammonia was scarcely affected. Perfusion of the isolated ileum with AU (0.5 ml/min) for 60 minutes resulted in an absorption of 59% of the solvent and 50 to 86% of each constituent. The rate of absorption was reduced after increment of the perfusion rate. In conclusion, the absorption of urinary constituents occurs rapidly and significantly. The absorptive capacity remains longer regardless the severity of histological changes of the ileal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗