[Determination of the intestinal absorption of cardiac glycosides by measurement of 3H-labelled glycosides in the portal venous blood and in the intestinal lymph of cats].
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Animals↗
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Synthesis, characterization and in situ intestinal absorption of different molecular weight scutellarin-PEG conjugates.
Highly water soluble esters of scutellarin with different molecular weight polyethylene glycol (PEG) were synthesized. The physicochemical properties, the stabilities under different conditions and the in situ intestinal absorption of the conjugates in rats were investigated. By PEG modification, greatly increased water solubility and a desirable partition coefficient were obtained. These compounds act as prodrugs i.e. breakdown occurrs in a predictable fashion: in vitro, the t1/2 of them in PBS buffer at pH 7.4 was above 12 h (37 degrees C), while in plasma a more rapid breakdown was observed (t1/2 1.5-3 h). PEGylation could enhance the absorption of scutellarin in rat intestine, and scutellarin, its PEG conjugates are absorbed through intestine mainly via passive transport. When the molecular weight of PEG increased from 200 to 1000 Da, the absorption of the conjugates decreased accordingly. The range of PEG molecular weight used for the PEGylation of scutellarin was about 400-1000 Da based on considerations of the yield, the stability and the absorption.
Animals↗
Effect of feeding raw legumes on intestinal absorption: a short review.
This review summarizes some of our own results relating with the effect of feeding raw legume diets on the intestinal absorption of sugars and amino acids. As compared to control well-fed animals, both in vivo and in vitro intestinal transport of these substrates are significantly inhibited in legume-fed rats and chickens.
Animals↗
Intestinal absorption of immunologically intact macromolecules in germfree colostrum-deprived piglets maintained on total parenteral nutrition.
We have compared the neonatal absorption of anti-bovine gamma-globulin (BGG) antibody supplied in colostrum or saline in three groups of piglets born and maintained under different environmental conditions to determine the effect of these conditions on the cessation of intestinal absorption of macromolecules (anti-BGG antibody), termed "closure." An enzyme-linked immunosorbent assay was used to estimate the concentration of anti-BGG antibody in sera from each group of piglets. Three stages of macromolecular absorption through the piglet's intestine could be detected. The first stage is a nonselective massive absorption of macromolecules (in milligram levels) that lasts up to 3 days in germfree (GF) colostrum-deprived or conventional colostrum-fed piglets but up to 5 days in GF piglets maintained on total parenteral nutrition. In this stage, absorption was significantly (r = .05) higher in piglets fed anti-BGG serum with colostrum than in piglets fed anti-BGG serum without colostrum on GF day 0 (31.28% vs 15.59%) and GF-total parenteral nutrition day 3 (3.08% vs 0.11%). Thus, whenever there was the ability to absorb a massive amount of macromolecules, the sow colostrum had an enhancing affect. Although there was a minor effect of environmental or orally received stimuli in delaying closure, absorption of macromolecules decreased in all piglets maintained either parenterally or enterally after day 3. Thus, intestinal closure to massive absorption of macromolecules in piglets is primarily time (age)-dependent. The second stage is a selective absorption of immunoglobulins in much smaller quantities (microgram levels), inasmuch as absorption of 0.02% to 0.1% was determined in all 5-day-old piglets.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Intestinal absorption mechanism of dipeptide angiotensin converting enzyme inhibitors of the lysyl-proline type: lisinopril and SQ 29,852.
The intestinal absorption mechanism of two nonsulfhydril lysyl-proline angiotensin converting enzyme (ACE) inhibitors, lisinopril (1) and SQ 29,852 (2; [(S)-1-[6-amino-2-[[hydroxy (4-phenylbutyl)-phosphinyl]oxy[-1-oxohexyl]-L-proline) were investigated in rats using a single-pass perfusion method. Compound 2 is well absorbed from rat jejunum, whereas lisinopril absorption is relatively low. The permeability of both ACE inhibitors is concentration dependent and is decreased by the dipeptide Tyr-Gly and by cephradine, indicating a nonpassive absorption mechanism via the peptide carrier-mediated transport system. Compound 2 is well absorbed by a nonpassive mechanism, in parallel with a small passive component. The estimated dimensionless carrier parameters for 2 are J*max = 0.16, Km = 0.08 mM, P*c = 2.0, and P*m = 0.25; for lisinopril, passive absorption is not significant and its absorption is nonpassive: J*max = 0.032, Km = 0.082 mM, and P*c = 0.39 (where J*max is the maximal flux, Km is the Michaelis constant, P*c is the carrier permeability, and P*m is the passive permeability). These results offer a mechanistic explanation for the prolonged ACE inhibition and the low oral bioavailability of lisinopril, and for the nonlinear pharmacokinetics of 2.
Angiotensin-Converting Enzyme Inhibitors↗
Prodrug and analog approaches to improving the intestinal absorption of a cyclic peptide, GPIIb/IIIa receptor antagonist.
PURPOSE: The purpose of this study was to test whether structural modifications improve the intestinal absorption of DMP 728 (cyclo(D-Abu-NMeArg-Gly-Asp-Amb)), a GPIIb/IIIa receptor antagonist. METHODS: In vitro permeabilities of prodrugs and analogs of DMP 728 across excised rat intestinal segments were determined. RESULTS: n-Butyl and n-octyl esters of DMP 728 were relatively stable during in vitro permeation of rat intestine. Intestinal permeation rates of these compounds were no greater than that of DMP 728, even though the octyl ester was much more lipophilic. A pivaloyloxymethyl ester, which was hydrolyzed to DMP 728 during intestinal permeation, also did not improve permeability. In another approach, analogs with an additional methyl substituent on various amide nitrogens were evaluated. Cyclo(D-Val-NMeArg-Gly-Asp-NMeAmb), cyclo(D-Abu-diN-MeLys-Gly-Asp-Amb), and cyclo(NMeGly-NMeArg-Gly-Asp-Amb) each had about 2-fold greater permeability than DMP 728. Two other analogs with improved permeability were linear Ac-D-Abu-NMeArg-Gly-Asp-Amb and a DMP 728 derivative in which the Asp was rearranged. An analog in which the charged amino acids were replaced by neutral amino acids had permeability similar to DMP 728. CONCLUSIONS: Within this series of peptides, hydrogen bonding tendency and structural constraint influenced intestinal permeation, but not always in ways consistent with the literature, whereas charge and lipophilicity were not shown to influence intestinal permeability. The failure of these approaches to improve permeation more significantly could be due to the influence of secretory transport.
Animals↗
Intestinal absorption of human insulin in pigs using delivery systems based on superporous hydrogel polymers.
In this in vivo study, novel delivery systems based on superporous hydrogel (SPH) and SPH composite (SPHC) polymers were used to improve the intestinal absorption of insulin in healthy pigs. Six female pigs of approximately 35 kg body weight were used. A cannula was inserted into the jugular vein for blood sampling and a silicone fistula in the duodenum for administration of gelatin capsules containing the delivery systems or insulin solutions. The delivery systems consisted of two components, (1) conveyor system made of SPH and SPHC; (2) core containing insulin. The core was inserted either into the conveyor system (core inside, c.i.) or attached to the surface of conveyor system (core outside, c.o.). The following intestinal formulations were investigated: c.i., c.o. and intraduodenal (i.d.) administration of insulin solutions. Subcutaneous (s.c.) injection of insulin was also investigated for reasons of comparison. Blood samples were taken and analyzed for insulin and glucose concentrations. Relative bioavalibility values of 1.3+/-0.4 and 1.9+/-0.7% were achieved for c.o. and c.i. administrations, respectively. The bioavalibility for i.d. administration of insulin solution was 0.5+/-0.2%. These results indicate that the absorption of insulin was slightly increased using SPH/SPHC-based delivery systems. Furthermore, a large variability was observed, probably due to physiological and metabolic changes during the experiments. Blood glucose levels were slightly decreased after the c.o. and c.i administrations, whereas these levels did not decrease after i.d. administration of insulin solutions. In conclusion, SPH/SPHC-based delivery systems are able to enhance the intestinal absorption of insulin and are, therefore, considered as promising systems for peroral peptide drug delivery. However, insulin delivery from these delivery systems under in vivo have to be improved.
Animals↗
Intestinal absorption and metabolism of chlorpheniramine enantiomers in rat.
Chlorpheniramine (CPAM) is a chiral antihistaminic drug commercialized as a racemic mixture. The intestinal absorption and metabolism of CPAM have been investigated in rat using in vivo (oral and IV administration), in situ (intestinal loop model), and in vitro (everted sac model) experiments. Oral and IV administrations of 20 mg/kg of the racemic mixture show that the pharmacokinetics of CPAM are stereoselective, with higher AUCs for the (+)-S-enantiomer compared to its antipode. The monodesmethyl metabolite (DCPM) was quantifiable in blood and its pharmacokinetics are stereoselective after oral but not after IV administration. Experiments using intestinal loops and everted sacs showed that the absorption is not stereoselective and that in vivo stereoselective formation of DCPM is presumably due to stereoselective hepatic metabolism. Moreover, the in vitro and in situ absorption of CPAM are not modified by modulators of P-glycoprotein and cytochromes P450 (cyclosporin A, ketoconazole).
Animals↗
Experimental studies on the influence of surfactants on intestinal absorption of drugs. Cefadroxil as model drug and sodium taurocholate as natural model surfactant: studies in rat colon and in rat duodenum.
The influence of the natural bile acid surfactant sodium taurocholate (CAS 81-24-3) on colic and duodenal (i.e. the proximal third of the small intestine) absorption of cefadroxil (CAS 50370-12-2) was studied using the in situ rat gut technique, and compared with the effect of sodium lauryl sulfate (CAS 151-21-3), the most widely used synthetic anionic surfactant. Previously, the stability, compatibility, and micelle-solubilization characteristics of taurocholate were assessed in order to correct, when necessary, the absorption results. White the passive absorption rate constants (kf, h-1) determined in colon in the presence of increasing lauryl sulfate concentrations showed an asymptotic value about 7-fold higher than that of cefadroxil alone, only a 2-fold higher value was obtained in the presence of taurocholate at similar concentrations. Therefore the natural surfactant would increase the polarity of the colic absorbent membrane much less than lauryl sulfate does (about 3.5 times). The effects of taurocholate on the duodenal absorption of cefadroxil, which is the sum of a single passive process and a simultaneous carrier-mediated transport, can be summarized as follows: 1. When the working concentration of cefadroxil is far from carrier saturation (0.1 mg/ml) a slight but clear net decrease in the apparent kf value is observed in the presence of increasing concentrations of the natural surfactant (from 3.0 to 2.3 h-1) 2. When the concentration of the antibiotic in the working fluid is above carrier saturation (10 mg/ml) the picture is reversed, and a slight net increase in kf in the presence of increasing concentrations of taurocholate (from 0.8 to 1.2 h-1) is found. This means that the effect of taurocholate as a noncompetitive inhibitor of active cefadroxil transport is very much smaller than that observed with lauryl sulfate. Moreover, the increase in passive absorption relative to the synthetic surfactant is also much smaller. On the basis of allometric considerations it could be concluded that for practical purposes taurocholate does not act as a substantial absorption modifier for cefadroxil, at least in the small intestine, the main absorption site of the antibiotic. It can, however, not be considered an inert ingredient, and therefore oral administration of cefadroxil far from that of taurocholate-containing preparations, and even from lipid-rich meals should be strongly recommended.
Algorithms↗
Studies on mechanisms of diarrhea induced by fusarenon-X, a trichothecene mycotoxin from Fusarium species; characteristics of increased intestinal absorption rate induced by fusarenon-X.
Fusarenon-X (F-X) is one of the trichothecene mycotoxins. F-X enhanced D-xylose absorption rate in rat everted intestinal sac. In the present work, the mechanism of the F-X-induced enhancement of intestinal D-xylose absorption rate was studied. F-X had no detectable effect on D-glucose absorption of everted rat intestine. When 10 mM of D-xylose was employed, a concomitant application of oxygen-free condition and low temperature failed to affect the D-xylose absorption of normal rat, but inhibited that of F-X-treated rat. When D-glucose concentration was 5 mM, the concomitant application of oxygen-free condition and low temperature depressed the D-glucose absorption of normal rat, while it did not reduce that in F-X-treated rat. These results suggested that the sugar translocation mechanism of F-X-treated rat intestine was different from that of normal one. F-X-induced enhancement of D-xylose absorption in everted intestinal sac may depend on the increase in permeability of the intestinal membrane which is derived from the histological and functional damage of the intestinal mucosa induced by F-X.
Animals↗
Intestinal absorption of oyster shell electrolysate.
High voltage electric current was passed through oyster shell powder for electrolysis. The crystalline shape of oyster shell electrolysate appeared to be quite different from that of CaO or CaCO3. Higher serum calcium values were achieved by oral administration of the same amount of as oyster shell electrolysate than as calcium carbonate in vitamin D-deficient rats, suggesting a better intestinal absorption of the former than the latter. In four patients with postoperative hypoparathyroidism with reduced intestinal calcium absorption, the same amount of elementary calcium as oyster shell electrolysate was more effective than calcium carbonate in raising serum calcium in the absence of vitamin D supplement. Oyster shell electrolysate was also more effective in suppressing serum parathyroid hormone concentration than calcium carbonate in two patients with secondary hyperparathyroidism with renal failure. Calcium thus appears to be more readily absorbed from oyster shell electrolysate than from calcium carbonate through intestinal barriers produced by insufficient vitamin D action.
Adult↗
Intestinal absorption and liver uptake of medium-chain fatty acids in non-anaesthetized pigs.
In order to study the rate of intestinal absorption and hepatic uptake of medium-chain fatty acids (MCFA), six growing pigs, mean body weight 65 kg, were fitted with a permanent fistula in the duodenum and with three catheters in the portal vein, carotid artery and hepatic vein respectively. Two electromagnetic flow probes were also set up, one around the portal vein and one around the hepatic artery. A mixture of octanoic and decanoic acids, esterified as medium-chain triacylglycerols, together with maltose dextrine and a nitrogenous fraction was continuously infused for 1 h into the duodenum. Samples of blood were withdrawn from the three vessels at regular intervals for 12 h and further analysed for their non-esterified octanoic and decanoic acid contents. The concentration of non-esterified octanoic and decanoic acids in the portal blood rose sharply after the beginning of each infusion and showed a biphasic time-course with two maximum values, one after 15 min and a later one between 75 and 90 min. Only 65% of octanoic acid infused into the duodenum and 54% of decanoic acid were recovered in the portal flow throughout each experiment. The amounts of non-esterified MCFA taken up per h by the liver were close to those absorbed from the gut via the portal vein within the same periods of time, showing that the liver is the main site of utilization of MCFA in pigs. These results have been discussed with a special emphasis laid on the possible mechanisms of the biphasic time-course of MCFA absorption and the incomplete recovery in the portal blood of the infused fatty acids.
Animals↗
Recent advances in carrier-mediated intestinal absorption of water-soluble vitamins.
Significant progress has been made in recent years toward understanding the mechanisms and regulation of intestinal absorption of water-soluble vitamins from the diet, especially those that are transported by a specialized carrier-mediated mechanism (i.e., ascorbic acid, biotin, folate, riboflavin, thiamin, and pyridoxine). The driving force involved in the uptake events and the molecular identity of the systems involved have been identified for a number of these vitamins. In addition, information about regulation of the uptake process of these micronutrients by intracellular and extracellular factors has been forthcoming. Furthermore, the 5' regulatory region of the genes that encode a number of these transporters has been characterized, thus providing information about transcriptional regulation of the transport events. Also of interest is the identification of existence of carrier-mediated mechanisms in human colonocytes that are capable of absorbing some of the vitamins that are synthesized by normal microflora of the large intestine. Although the contribution of the latter source of vitamins toward overall host nutrition is not clear and requires further investigations, it is highly likely that it does contribute toward the cellular homeostasis of these vitamins in the localized colonocytes.
Animals↗
Further mechanistic study on intestinal absorption enhanced by unsaturated fatty acids: reversible effect by sulfhydryl modification.
In order to study the relationship between the sulfhydryl (SH) modification of membrane-associated proteins and the oleic acid-induced permeability enhancement of the colonic mucosa, in vitro and in situ absorption studies were performed using rat colon and carboxyfluorescein as an impermeable dye. The pretreatment of the mucosa with diamide, a bifunctional sulfhydryl modifier, in in vitro experiments with the everted colonic loops reduced the absorption enhancing effect of oleic acid in a concentration-dependent manner, less inhibitory effect, though just a little, was observed as compared to N-ethylmaleimide. The inhibition caused by the addition of diamide was absolutely restored by exposure of the mucosa to dithiothreitol. On the other hand, these SH modifiers showed no pronounced effect on the in vivo permeability of quinine which is well-known to be absorbed by a passive transport system mainly via the membrane lipid bilayer. These results obtained in the present study have identified an important role of the functional SH groups of membrane proteins on modulating the permeability alteration of the mucosal epithelium provoked by oleic acid. Furthermore, the SH proteins have been revealed as being unimportant in the intestinal absorption of lipoid-soluble compounds.
Animals↗
INTESTINAL ABSORPTION OF VITAMIN A.
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Absorption↗
[Physiology of intestinal absorption].
Hydrolysis of dietary constituents is necessary to allow nutrients absorption by the small intestinal enterocytes. The digestion process takes place in the intestinal lumen, in the brush border membrane, in the enterocyte, and is mediated by a large number of hydrolases secreted in the gastrointestinal tract or produced by the epithelial cells and localized in the brush border. Nutrients are essentially absorbed via a transcellular route across enterocyte cell membranes to enter bloodstream or lymphatic circulation. Transport of nutrients across apical or basolateral membranes occur by active or facilitated mechanisms involving specific transporters. Water, electrolytes and small molecules can be partly absorbed via paracellular pathway. Tight junction permeability is regulated by osmolarity of intercellular space, definite nutrient concentrations in lumen, and activity of brush border membrane transporters.
Biological Transport↗
Proceedings: Intestinal absorption of tetrahydrobiopterin and pterolic acid in man: a comparison of models for the transport of folates across the small intestine.
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Folic Acid↗
The kinetics of intestinal absorption of radiohippuran in control subjects and in patients with intestinal malabsorption.
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Computers↗