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PubMed1977

Intestinal oxalate absorption. I. Absorption in vitro.

Enteric hyperoxaluria and oxalate urolithiasis in patients with ileal resection seem to be caused by intestinal hyperabsorption of oxalate. The mechanism responsible for hyperabsorption of oxalate is not known. Intestinal transport of oxalic acid was therefore examined by an in vitro technique in rat intestine. Oxalic acid was absorbed by a mechanism of simple passive diffusion. The rate of absorption decreased from the colon to the duodenum (colon greater than ileum greater than jejunum greater than duodenum). Bile acids enhanced oxalic acid absorption in the large and small intestine and increased extracellular space; calcium, however, markedly decreased mucosal-serosal transport of oxalic acid. Cholestyramine known to reduce oxalate excretion in hyperuxaluria associated with ileal resection did not directly affect absorption of oxalic acid, but decreased the enhanced absorption of oxalic acid induced by bile acids. The results suggest that the beneficial therapeutic effect of cholestyramine in hyperuxaluria is rather mediated by its bile acid binding activity than by direct binding of oxalic acid.

Animals↗
PubMed1991

Lymphatic absorption of structured glycerolipids containing medium-chain fatty acids and linoleic acid, and their effect on cholesterol absorption in rats.

The effects of various structured triglycerides containing medium-chain (caprylic or capric acids) and long-chain (linoleic acid) fatty acids on fatty acid and cholesterol absorption were studied in lymph-cannulated rats. A considerable portion of capric and caprylic acid was absorbed through the lymph duct, although to a lesser extent than was linoleic acid. Capric and linoleic acid located at the 2-position of 2-decanoyl-1,3-dilinoleoyl-glycerol (18:2/10:0/18:2) and 2-linoleoyl-1,3-didecanoyl-glycerol (10:0/18:2/10:0), respectively, tended to be absorbed more efficiently than those located at the 1- and 3-position or those from tricaprin (10:0/10:0/10:0) or trilinolein (18:2/18:2/18:2). A similar trend was observed when the medium-chain fatty acid was caprylic acid instead of capric acid. Caprylic acid absorption from 2-octanoyl-1,3-dilinoleoyl-glycerol (18:2/8:0/18:2) was significantly greater (p less than 0.05) than from 2-linoleoyl-1,3-dioctanoyl-glycerol (8:0/18:2/8:0) or tricaprylin (8:0/8:0/8:0). Preferential absorption of caprylic and linoleic acid was not observed when the 1 to 2 and the 2 to 1 mixtures of 8:0/8:0/8:0 and 18:2/18:2/18:2, respectively, were administered. The structured lipids did not affect the lymphatic absorption of cholesterol. The results suggest that structured triglycerides composed of medium-chain fatty acids and linoleic acid may be more useful for the treatment of lipid malabsorption than are mixtures of medium-chain triglyceride (MCT) and long-chain triglyceride (LCT).

Absorption↗
PubMed1991

Percutaneous absorption of parathion in vitro in porcine skin: effects of dose, temperature, humidity, and perfusate composition on absorptive flux.

The effect of environmental factors on the percutaneous absorption of parathion in excised porcine skin was assessed in a flow-through diffusion cell system by varying the temperature (T), relative humidity (%RH), perfusate flow rate (F), and composition (porcine serum) at three parathion doses (4, 40, and 400 micrograms/cm2) compared to standard conditions (air temperature = 37 degrees C, perfusate temperature = 37 degrees C, %RH = 60, flow rate = 4 ml/hr, and standard bovine serum albumin medium). Parathion absorption was assessed by monitoring total radiolabeled activity appearing in the perfusate over time. High relative humidity significantly increased parathion penetration, as did two elevated temperature conditions. The effects of flow rate and perfusate composition were variable and dose dependent. In the present studies, lower applied doses appeared to be more sensitive to changes in the environmental conditions studied. These results suggest that these parameters have independent and different degrees of effect on parathion percutaneous absorption. Experimental conditions should be strictly controlled and dose-response studies need to be conducted when evaluating transdermal studies. Finally, if similar effects occur in vivo, the risk assessment calculations on percutaneous absorption should take these parameters into consideration.

Animals↗
PubMed2003

Analysis and prediction of absorption behavior of colon-targeted prodrug in rats by GI-transit-absorption model.

The gastrointestinal-transit-absorption (GITA) model is useful for the analysis and the prediction of the absorption behavior of drugs orally administered as solutions. In the present study, we tried to predict the plasma concentration-time profile of a colon-targeted prodrug, salicylazosulfanilic acid (SASA), and its parent drug, 5-aminosalicylic acid (5-ASA) which is regenerated after dosing. Prediction of plasma concentration-time profiles for SASA and 5-ASA was performed based on the GITA model using parameters describing GI-transit kinetics, the absorption in each GI segment, and the regeneration of 5-ASA in cecum. Plasma concentration-time profiles of both SASA and 5-ASA after oral administration of SASA were predicted very well by introducing a factor for the first-pass elimination of 5-ASA into the GITA model. The simulation study using the parameters obtained in the present study showed that about 94.7% of SASA reaches the cecum, where 5-ASA is regenerated very rapidly and 76.0% of 5-ASA is absorbed. Furthermore, the bioavailability of 5-ASA was estimated to be 0.330 because of the first-pass elimination through both cecum and liver. In conclusion, the absorption behaviors of a prodrug and its regenerated parent drug can be predicted very well and be clarified successfully using the GITA model.

Animals↗
PubMed2001

Bioadhesive starch microspheres and absorption enhancing agents act synergistically to enhance the nasal absorption of polypeptides.

This paper investigates the effect of starch microspheres on the absorption enhancing efficiency of various enhancer systems in formulations with insulin after application in the nasal cavity of sheep. The enhancers studied were lysophosphatidylcholine, glycodeoxycholate and sodium taurodihydroxyfusidate, a bile salt derivative. The enhancers were selected on the basis of their perceived or proven mechanism of action and worked predominantly by interacting with the lipid membrane. The bioadhesive starch microspheres were shown to increase synergistically the effect of the absorption enhancers on the transport of the insulin across the nasal membrane. Dependent on the potency of the enhancer system the increment in absorption enhancement was shown to be from 1.4 times to 5 times that obtained for the absorption enhancer in solution.

Absorption↗
PubMed1999

Impact of regional intestinal pH modulation on absorption of peptide drugs: oral absorption studies of salmon calcitonin in beagle dogs.

PURPOSE: To investigate the relationship between the modulation of intestinal pH and the oral absorption properties of a model peptide drug, salmon calcitonin (sCT), in conscious beagle dogs. METHODS: Studies were performed to characterize the disintegration of the formulation, intestinal pH changes, and the appearance of the peptide in the blood. Enteric-coated formulations containing sCT and various amounts of citric acid (CA) were tethered to a Heidelberg capsule (HC) and given orally to normal beagle dogs. Blood samples were collected and analyzed by radioimmunoassay (RIA). Intestinal pH was continuously monitored using the Heidelberg pH capsule (HC) system. The integrity of the HC-delivery system tether was verified by fluoroscopy. RESULTS: The intra-individual variation in gastric emptying (GE) of the delivery system was large. There were also large inter-individual differences in the disintegration and absorption properties of the various formulations. However, the peak plasma concentrations of sCT were always observed when the intestinal pH declined. The average baseline intestinal pH was 6.1 +/- 0.2 (mean +/- SEM, n = 12). The intestinal pH reduction was 2.6 +/- 0.4 (mean +/- SEM, n = 12, ranged from 0.5 to 4.0 units from baseline). There was a good correlation between the time to reach the trough intestinal pH (t(pH,min)) and time to reach the peak plasma concentration (tconc,max)) of sCT (t(conc,max) = 0.95 x t(pH,min) + 14.1, n = 11, r2 = 0.91). Plasma Cmax and area under the curve (AUC) increased with increasing amounts of CA in the formulations. CONCLUSIONS: The results of these studies demonstrate that the oral absorption properties of a model peptide drug, sCT, can be modulated by changing intestinal pH. sCT is a substrate for the pancreatic serine protease trypsin which has maximal activity at pH 5 to 6. Reducing intestinal pH presumably stabilizes sCT in the GI tract enabling greater absorption of the intact peptide.

Absorption↗
PubMed1994

Nasal absorption in the rat. III. Effect of lysophospholipids on insulin absorption and nasal histology.

The intranasal absorption enhancing and histological effects of a range of lysophospholipids has been investigated in the rat. Blood glucose levels fell rapidly following the administration of insulin (8 IU/kg) in combination with lysophosphatidylcholines (LPC; 0.625% w/v) which had ten or more carbon groups in their fatty acid chain. The effect of the LPC-caproyl (C6) was comparable to that of an unenhanced insulin formulation; the enhancing effect of LPC-decanoyl (C10) was similar to that of an LPC-palmitoyl/stearoyl (C16/C18) for similar concentrations. The effect of LPC-decanoyl was reduced with concentration but was still significant at 0.2% w/v (5mM). Lysophosphatidylglycerol (LPG) had a marked insulin absorption enhancing effect even at 0.0625% w/v. The histological effects of LPC-caproyl were similar to those of an unenhanced insulin formulation, while co-administration of LPC-decanoyl resulted in evidence of epithelial interaction. LPG (0.5% w/v) resulted in similar histological changes as LPC (0.625% w/v) (1), but at 0.0625% w/v no significant changes in epithelial integrity were observed. The length of the fatty acid residue of lysophospholipids was identified as an important factor for intranasal absorption enhancing activity. The nature of the polar head group may also have an influence. Increased insulin absorption was not necessarily accompanied by severe disruption of the nasal epithelium. Careful selection of lysophospholipid type and concentration may enable therapeutic drug levels to be achieved via the nasal route without prohibitive toxic effects.

Absorption↗
PubMed1976

Food iron absorption in human subjects. IV. The effects of calcium and phosphate salts on the absorption of nonheme iron.

The influence of physiological levels of calcium and phosphorus on the absorption of nonheme iron from a semisynthetic meal was evaluated. Each of the 34 participating subjects received two to four test meals. In three studies where both calcium and phosphate were added, absorption of nonheme iron was reduced to 27 to 47% of that absorbed when no salts were added. However, with the single addition of either calcium or phosphate to the test meals no significantly inhibiting effect was observed. As the absorption of nonheme iron was significantly reduced only with the combined addition of calcium and phosphate, it is suggested that a calcium-phosphate-iron complex forms which inhibits iron absorption.

Absorption↗
PubMed2003

Reference range for gastrointestinal oxalate absorption measured with a standardized [13C2]oxalate absorption test.

PURPOSE: Hyperoxaluria is a prominent risk factor for calcium oxalate urinary stones. Oxalate in urine is synthesized in the body or absorbed from food in the gastrointestinal tract. The amount of oxalate absorbed by patients with calcium oxalate stones may vary from a few percent to 50% of the dietary intake. Reference values for oxalate absorption measured under a standardized diet have never been attained in sufficient numbers from healthy individuals. Therefore, to our knowledge we collected for the first time the values required to interpret test results in patients with recurrent urinary stones. MATERIALS AND METHODS: A total of 120 healthy volunteers, including 60 females and 60 males, received an identical standard diet on 2 consecutive days. On the morning of day 2 a capsule containing 0.37 mmol. sodium [13C2]oxalate (not radioactive) was ingested with water. Urinary oxalate was measured by gas chromatography-mass spectrometry. Absorption at a fixed 800 mg. daily Ca input is expressed as a percent of the labeled oxalate dose. RESULTS: For the standardized [13C2]oxalate absorption test the reference range in 95% of the 120 volunteers was 2.2% to 18.5% (mean +/- SD 7.9% +/- 4.0%). The repeatability of the standardized test was determined in 26 of the 120 volunteers by repeating the test twice. The mean intra-individual SD was 3.39% +/- 1.68%. CONCLUSIONS: We assessed reference values of intestinal oxalate absorption using a standardized diet. Interindividual and intra-individual variance was high.

Absorption↗
PubMed1976

Absorption from different types of iron tablets - correlation between serum iron increase in total absorption of iron.

The absorption of iron from three different iron tablets - rapidly-disintegrating ferrous sulphate and ferrous carbonate tablets and slow-release ferrous sulphate tablets - was studied in healthy subjects with a serum iron technique and by whole-body counter measurements. A solution of ferrous sulphate was used as a reference. There were no differences in the absorption from the ferrous sulphate preparations, but the ferrous carbonate tablets were less well absorbed. Good correlation was found between the maximal serum iron response and the total absorption of iron and it was concluded that serum iron studies may be used for semiquantitative measurements of iron absorption in comparative studies on different iron preparations.

Adult↗
PubMed1988

Absorption of bile acids in dog as determined by portal blood sampling: evidence for colonic absorption of bile acid conjugates.

The intestinal phase of enterohepatic circulation, such as site and state of bile acid absorption, along the length of the intestinal tract has been speculated but not directly quantitated. In order to gain insight into the actual state of intestinal absorption of bile acid, the bile acid composition of portal blood from various segments of the intestinal tract was studied in dogs after loading endogenous bile acid by injection of caerulein. Total and unconjugated bile acids were determined with and without enzymatic hydrolysis, respectively. The amount of conjugated bile acids was calculated by subtracting unconjugated from total bile acids. Quantitation of cholic, chenodeoxycholic, deoxycholic and lithocholic acids and their conjugates was carried out by gas chromatography/mass spectrometry/selected ion monitoring with deuterated bile acids as internal standards. The major site of absorption of taurine-conjugated bile acid, a major conjugate form in the dog, was the distal small intestine. In addition, a considerable amount of cholic acid was found to be absorbed from the distal large intestine, the majority of which was still in the conjugated form. The pronounced absorption of the unconjugated secondary bile acid from the large intestine suggests the very active formation of the secondary bile acid in situ.

Animals↗
PubMed1988

Bicarbonate absorption stimulates active calcium absorption in the rat proximal tubule.

To evaluate the effect of luminal bicarbonate on calcium reabsorption, rat proximal tubules were perfused in vivo. Perfusion solution contained mannitol to reduce water flux to zero. Total Ca concentration was measured by atomic absorption spectrometry, Ca ion concentration in the tubule lumen (CaL2+) and the peritubular capillary (CaP2+), and luminal pH (pHL) with ion-selective microelectrodes and transepithelial voltage (VTE) with conventional microelectrodes. When tubules were perfused with buffer-free Cl-containing solution, net Ca absorption (JCa) averaged 3.33 pmol/min. Even though VTE was 1.64 mV lumen-positive, CaL2+, 1.05 mM, did not fall below the concentration in the capillary blood, 1.07 mM. When 27 mM of Cl was replaced with HCO3, there was luminal fluid acidification. Despite a decrease in VTE and CaL2+, JCa increased to 7.13 pmol/min, indicating that the enhanced JCa could not be accounted for by the reduced electrochemical gradient, delta CCa. When acetazolamide or an analogue of amiloride was added to the HCO3 solution, JCa was not different from the buffer-free solution, suggesting that HCO3-stimulated JCa may be linked to acidification. To further test this hypothesis, we used 27 mM Hepes as the luminal buffer. With Hepes there was luminal fluid acidification and JCa was not different from the buffer-free solution but delta CCa was significantly reduced, indicating enhanced active calcium transport. We conclude from the results of the present study that HCO3 stimulates active Ca absorption, a process that may be linked to acidification-mediated HCO3 absorption.

Absorption↗
PubMed1988

Studies on intestinal lymphatic absorption of drugs. II. Glyceride prodrugs for improving lymphatic absorption of naproxen and nicotinic acid.

A series of alpha- and beta-monoglycerides and triglyceride derivatives of naproxen or nicotinic acid were synthesized and investigated in order to elucidate the molecular form of the derivative with properties that enhanced lymphatic absorption. The lymphatic absorption rate was increased by adjusting the length of an n-alkyl chain introduced between the alpha- or beta-position of glycerol and the drug residue. The alpha- and beta-monoglyceride derivatives (containing an n-alkyl chain) were approximately equal in lymphatic absorption rates, but differed markedly in the concentration of the di- and triglyceride analogues in the lymph lipids. The lymphatic absorption of triglyceride derivatives, drugs combined directly with beta-position of glycerol, was low in comparison with the monoglyceride derivatives. Compared with nicotinic acid, the alpha-monoglyceride derivative (n-alkyl chain length, Cn = 20) of nicotinic acid provided a higher AUC0-8 h value of free nicotinic acid and maintained a lower level of free fatty acids in blood.

Animals↗
PubMed1982

Intestinal absorption of several beta-lactam antibiotics. III. Competitive inhibition behavior among zwitterionic beta-lactam antibiotics in the rat intestinal absorption.

Competitive inhibitory behavior among zwitterionic beta-lactam antibiotics in the rat intestinal absorption process was examined. Intestinal absorption of cephradine and cephalexin was significantly inhibited by cyclacillin. The mutual inhibition between these amino-cephalosporins was also observed. On the other hand, in the pretreatment experiments with cyclacillin, it was found that absorption of cephradine was significantly inhibited, but the inhibitory effect of cyclacillin was not observed for cephalexin. These results showed that cephradine had a common carrier-mediated transport mechanism with cyclacillin which is not present in the absorption process of cephalexin. It was postulated that the mutual inhibition between cephradine and cephalexin is based on the competitive inhibition in the accumulation or uptake by the intestinal mucosa.

Animals↗
PubMed1984

Drug absorption from the gastrointestinal tract and immunity: the mechanism of the decreased absorption of salicylic acid during systemic anaphylaxis. II.

Rats were intraperitoneally immunized with ovalbumin (egg albumin) with incomplete Freund's adjuvant, and the effect of intravenous challenge with ovalbumin on the intestinal blood flow was measured by means of hydrogen clearance method. The intestinal blood flow was significantly reduced by the antigen challenge in ovalbumin-immunized rats compared to the non-immunized rats. However, no significant change was observed on the intestinal blood flow in rats without challenge of the antigen. Moreover, the blood flow reduction was not found in ovalbumin-immunized rats challenged with bovine gamma-globulin. The effect was maintained for at least 16 weeks after the third immunization, but the reduced blood flow was gradually restored to the control level. The decrease in both blood flow and absorption of salicylic acid was recovered by nearly 70% of the control level when high dose of theophylline or caffeine was administered intravenously. In the case of gastric absorption during systemic anaphylaxis, similar results were also obtained by means of in situ loop technique. The decreased absorption of salicylic acid from the rat stomach also correlate with the reduced gastric blood flow. These findings suggest that the decreased absorption of salicylic acid from the gastrointestinal tract might be affected by the reduced blood flow during systemic anaphylaxis.

Anaphylaxis↗
PubMed1992

Contribution of interstitial diffusion in drug absorption from perfused rabbit muscle: effect of hyaluronidase on absorption.

[3H]Water and [14C]inulin were injected into perfused rabbit muscle with or without hyaluronidase (300 units/ml) and their absorption into venous effluent from muscle was determined. Hyaluronidase accelerated the absorption of both compounds but the enhancement of [14C]inulin was much larger than that for [3H]water. The pharmacokinetic analysis of venous appearance curves based on a physiological diffusion model elucidated that interstitial diffusion of [14C]inulin was remarkably increased by hyaluronidase treatment, suggesting the existence of steric hindrance for it by the polysaccharide network under normal conditions. Enhancement of [3H]water diffusion was also detected although enhancement ratio was about one-half of that of [14C]inulin. Mean time necessary for each process was calculated using the statistical moment concepts. The results suggested predominant contribution of the interstitial diffusion process and secondary and little contribution of local perfusion flow and permeation process across the capillary wall, respectively, in total absorption of [14C]inulin. Effect of hyaluronidase on transcapillary movement of [14C]inulin was studied using an in vitro diffusion experiment with cultured endothelial cell monolayer and no enhancing effect was shown on [14C]inulin transport across the cell monolayer. The contribution of the local perfusion flow, on the other hand, was shown to be almost equivalent to that of the diffusion process in the total absorption of [3H]water.

Absorption↗
PubMed2003

A modified two-portion absorption model to describe double-peak absorption profiles of ranitidine.

BACKGROUND: The pharmacokinetics of oral drugs exhibiting double peaks cannot be adequately described by using conventional compartmental models. OBJECTIVE: To propose and evaluate a modified two-portion absorption model based on physiological and biopharmaceutical considerations to describe the double-peak concentration-time curve of ranitidine. MODEL DESIGN: The proposed model assumes that oral ranitidine is absorbed sequentially in two portions due to delayed gastric emptying, and thus includes a gut compartment in addition to the central and peripheral compartments. METHODS: Validation of the model was performed with respect to structural identifiability, parameter estimability and model applicability. Using initial estimates of parameters obtained from previous intravenous data, the model was used to fit oral ranitidine data from six subjects who manifested clear double-peak concentration-time profiles as well as from six subjects who showed irregular but apparent single-peak concentration-time curves. RESULTS: Based on goodness-of-fit criteria, the model fitted well for both double-peak and single-peak concentration-time curves of ranitidine (for the two groups: weighted residual sum of squares, 0.044 +/- 0.027 and 0.054 +/- 0.036; correlation between observed and model predicted concentrations, 0.995 +/- 0.003 and 0.995 +/- 0.005). Simulation studies with concentrations generated with 10% normally distributed random error showed that all model fitted parameters had good accuracy and reasonable precision. The mean percentage bias ranged from -7.0 to 28.6%, and the coefficient of variance was within 30% for the majority of parameters compared with the theoretical values. CONCLUSION: The modified two-portion absorption model may afford a useful approach to characterise the absorption phase and estimate pharmacokinetic parameters for drugs with two absorption peaks.

Adult↗
PubMed1975

Thiamine absorption in the rat. ii. intestinal alkaline phosphatase activity and thiamine absorption from rat small intestine in-vitro and in-vivo.

The correlations between intestinal alkaline phosphatase (IAP) activity and thiamine absorption and glucose absorption were studied in the rat. An everted sac in-vitro technique was used in adult rats whereas in-vitro experiments were performed in young rats 10 days old. All incubation experiments were done with 14-C-labeled thiamine. The patterns of IAP activity along the small intestines differed greatly between young and adult rats but were closely paralleled by the distribution of active thiamine transport in adult rats and thiamine absorption in young rats, respectively. When IAP was specifically inhibited in adult rats by L-phenylalanine active thiamine transport in-vitro was abolished. No correlation was found between IAP activity and active transport or glucose in-vitro, nor did inhibition of the enzyme in any way affect glucose transport capacity. It is suggested that the enzyme intestinal alkalinephosphatase is involved in the process of active thiamine absorption.

Age Factors↗