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At least 127 records · Page 7Linked to original sources
PubMed1987

Studies on drug absorption from oral cavity. II. Influence of the unstirred water layer on absorption from hamster cheek pouch in vitro and in vivo.

The influence of the unstirred water layer (UWL) adjacent to the membrane surface of the hamster cheek pouch on absorption was studied in vitro and in vivo. The tissue uptake rate of 14C-laurylalcohol was determined in vitro and the value of the effective resistance of UWL (RW) was calculated. RW values were reduced by increasing the stirring rate of the mucosal solution. In vitro permeation of 14C-benzoic acid into the serosal compartment was also increased in the well-stirred condition. Thus, the existence of UWL as an effective diffusion barrier for drug absorption from the hamster cheek pouch was suggested. To clarify the influence of the existence of UWL on the absorption in vivo, the apparatus for luminal stirring was newly devised. When the luminal solution was well-stirred, the absorption of benzoic acid in the lower pH region significantly increased, resulting in the disappearance of the shift of pH-absorption curve for benzoic acid. Furthermore, the luminal stirring increased the absorption rate constant for salicylic acid. From these experimental results, it is suggested that UWL plays a part of barriers against drug permeation in the hamster cheek pouch.

Administration, Buccal↗
PubMed1986

Studies on drug absorption from oral cavity: physicochemical factors affecting absorption from hamster cheek pouch.

A new experimental method using a hamster cheek pouch in vivo for studying absorption processes across the keratinized oral mucous membrane was developed and some characteristics of the oral-mucosal absorption were clarified. A positive correlation between the absorption rate and the lipophilicity was observed in 18 aromatic compounds examined. The absorption of ionizable compounds was poor in the ionized form. These results suggest that the absorption from the keratinized hamster cheek pouch is due to a passive diffusion mechanism and obeys pH-partition hypothesis. The systemic transfer of salicylic acid after intra-cheek-pouch administration could be approximated by the first-order absorption model including a lag time process and the plasma levels found were consistent with this model.

Absorption↗
PubMed1990

Combinative improving effect of increased solubility and the use of absorption enhancers on the rectal absorption of uracil in beagle dogs.

An improvement of the rectal absorption of uracil was examined by the application of absorption enhancers in addition to the increased solubility of uracil. Uracil was ground with additives such as MgO, sodium 2,6-dihydroxybenzoate, human serum albumin or hydroxypropylmethylcellulose acetate succinate. Aqueous, oily and powdery formulations, which consisted of the ground mixtures, nicotinamide, urea and absorption enhancers such as polyoxyethylene (23) cetylether (BC-23) or sodium caprate, were prepared. Uracil solubility in the aqueous formulations was increased about 4-13 times that in the corresponding control formulations. When rectally administered to beagle dogs, marked increases in the plasma uracil level were observed in some of the cases of aqueous and oily formulations. In the powdery formulations and formulations containing macromolecular additives, however, absorption improvements was not observed. The results indicated that an improvement in the absorption of uracil was caused by the combinative improving effect of the increased uracil solubility and the promoting effect of absorption enhancers.

Absorption↗
PubMed1990

Studies on sustained-release suppositories. III. Rectal absorption of morphine in rabbits and prolongation of its absorption by alginic acid addition.

Rectal absorption of morphine from various kinds of suppository bases was investigated. The extent of bioavailability of morphine by rectal administration varied with the bases used (30.5-97.5%), but every value was higher than that in the case of oral administration (13.5%). Witepsol bases were preferable to macrogol base for the rectal absorption of morphine. In particular, Witepsol S-55 or W-35 gave a higher plasma peak level than H-15 or E-75, whereas the difference in the mean residence times obtained from these bases could not be regarded as significant. Sustained-release suppositories of morphine could be prepared simply by mixing alginic acid (Alg) with morphine in a suppository base. Further, prolonged rectal absorption could be obtained by using these sustained-release suppositories, and the absorption rate was controlled by the amount of Alg added. It seems likely that the sustained release was due to the binding of morphine to Alg from the results of partition coefficient and binding ratio measurements in aqueous solution. The rapid initial absorption and the subsequent prolonged absorption of morphine simultaneously obtained from the morphine-Alg suppository may be useful in the clinical context.

Alginates↗
PubMed1993

Effect of intestinal blood flow on absorptive site blood flow and lysine absorption as examined in situ in Holstein calves.

Total blood flow from an intestinal segment (TBF) was altered to determine effects on blood flow at the absorptive site (ASBF) and lysine absorption. Venous blood flow was restricted using a peristaltic pump to 20, 35, 50, 65, and 80% of the initial unrestricted rate. Lysine absorption and ASBF were determined from recovery of 14C and 3H in blood from intestinally perfused [14C]L-lysine and 3H2O, respectively. Fluid flux in the intestinal lumen was estimated from the difference in polyethylene glycol concentrations in luminal infusate and effluent. Restriction of TBF proportionally reduced ASBF, which composed 3 to 6% of TBF. Lysine absorption was reduced linearly during reduction of TBF. Fluid absorption varied among calves but was independent of TBF. Differences between loss of radioactive marker from perfusate and recovery in blood suggested a loss of 3H2O from the intestinal segment that was independent of TBF. Changes in blood flow to the small intestine may affect nutrient absorption in ruminants.

Animals↗
PubMed1984

Estriol: absorption after long-term vaginal treatment and gastrointestinal absorption as influenced by a meal.

This study was designed to evaluate the vaginal absorption of estriol when given as a 21-day treatment. Vaginal absorption was compared with the oral absorption of a known estriol preparation (TriovexR, Leo AB, Sweden). One mg of estriol was administered intravaginally once a day for 21 days to 6 menopausal women. Plasma concentrations of unconjugated estriol were measured by a specific RIA-method at frequent intervals during 24 hours on the first and 21st day of treatment. One month later, 10 mg of estriol was given once orally and plasma estriol concentrations were measured in the same way. At vaginal administration, the absorption of estriol was very effective. When measured on the 21st day, the absorption had declined significantly but was still nearly in the same range as after oral administration of 10 mg of estriol. At oral administration, there was an initial plasma estriol elevation for 3 hours only followed by a second one immediately postprandially. It is concluded that estriol is readily absorbed from the vagina, but the absorption does decline significantly during prolonged treatment. A large single oral dose of estriol provides initially a high plasma estriol concentration but also a second one induced by eating a meal, possibly indicating an enterohepatic recirculation of estriol.

Administration, Oral↗
PubMed1977

Intestinal absorption of alpha-tocopherol in the unanesthetized rat. The influence of luminal constituents on the absorptive process.

3H-alpha-tocopherol intestinal absorption was studied in the unanesthetized rat. The rate of alpha-tocopherol absorption remained linear over a wide range of concentrations (4 nM to 400 micrometer). Increasing the sodium taurocholate concentration in the micellar infusate up to 15 mM did not increase the rate of absorption of the vitamin. Addition of long-chain fatty acids to the micellar infusate decreased the absorption rate of the vitamin (p less than 0.05). The decrease was most significant (p less than 0.01) following the addition of the polyunsaturated linolenic (C18:3) acid. Increasing the hydrogen ion concentration in the perfusate increased the absorption rate of alpha-tocopherol. The present experiments in vivo support the conclusions drawn from in vitro uptake experiments which indicated that alpha-tocopherol is absorbed by a passive diffusion process. These experiments indicate that micellar expansion with polyunsaturated fatty acids interferes with the absorption of alpha-tocopherol and may result in deficiency of the vitamin.

Animals↗
PubMedDate not supplied

Absorption of amino acids in different parts of the small intestine in growing pigs. III. Absorption of constituents of protein hydrolysates.

The study was performed on pigs weighing 50-75 kg with temporarily isolated loops of the proximal, middle and distal small intestine. Isolated segments were perfused with enzymic hydrolysates of known amino acids in free form and bound to peptides and proteins. Four hydrolysates were used from: casein I (CI), casein II (CII), soya bean protein (S) and gelatin (G). The absorption of nitrogen from all hydrolysates was least in the proximal small intestine (up to 7 g/m/24 h); there were no significant differences in nitrogen absorption between the other parts. The nitrogen absorption from the hydrolysates varied and was highest for CI and lowest for G. The rates of absorption of various amino acids were different, and were influenced by the proportions and composition of proteins, peptides, and free amino acids in the hydrolysates. However, the rates of absorption of methionine, arginine, leucine and phenylalanine were higher than those of lysine, threonine and histidine irrespective of the hydrolysate source. The peptide fraction of the hydrolysates disappeared from the lumen of the intestine more rapidly than did the amino acid fraction; this suggests that proteases and peptidases in the intestinal mucosa play an important role in the process of amino acid absorption.

Amino Acids↗
PubMed1995

Intestinal strontium absorption: from bioavailability to validation of a simple test representative for intestinal calcium absorption.

Calcium absorption tests have rarely been validated for being representative for absolute bioavailability (true absorption) or for intraindividual variation. Therefore, we investigated the reproducibility of the absolute bioavailability of strontium chloride, a marker for intestinal calcium absorption, in healthy male volunteers (n = 8) by measuring the area under the plasma strontium concentration-time curve after oral and intravenous administration of strontium. Subsequently, we selected a simple test variable as being representative of absolute bioavailability. The mean absolute bioavailability (+/- SD) was 25% +/- 7%. The best test variable appeared to be the fractional absorption at 240 min (Fc240) after oral intake, which demonstrated the highest correlation with absolute bioavailability (r = 0.66). The intraindividual variations of the data for this variable and for the absolute bioavailability are similar to those described for various absorption tests based on the use of calcium isotopes. Thus, the Fc240 of strontium offers the potential of a simple clinical test for use as a measure of intestinal calcium absorption and its modulation.

Adult↗
PubMed1983

Vaginal absorption of a potent luteinizing hormone-releasing hormone analogue (leuprolide) in rats III: Effect of estrous cycle on vaginal absorption of hydrophilic model compounds.

The effect of estrous cycle stages on vaginal absorption was determined by the use of insulin, phenolsulfonphthalein, and salicylic acid as hydrophilic model compounds. Absorption of these compounds was markedly affected by the stage, possibly due to the change of transport rate through the pore-like pathways. The absorption of phenolsulfonphthalein during proestrus and estrus is roughly one-tenth of that during metestrus and diestrus. An increase of the nonionized form of salicylic acid, produced by a lowered pH, resulted in an enhancement of absorption during proestrus and diestrus; higher contribution of the transport through the cell membrane possibly reduced an effect of the estrous cycle. However, consecutive daily administration of leuprolide halted the cycle at diestrus and reduced the cycle effect on the vaginal absorption of phenolsulfonphthalein; when the treatment was started at any of the four stages of the cycle, vaginal absorption was enhanced approximately 20%, with less variance than that observed in normal diestrous rats.

Animals↗
PubMed1990

Bile salt-fatty acid mixed micelles as nasal absorption promoters of peptides. I. Effects of ionic strength, adjuvant composition, and lipid structure on the nasal absorption of [D-Arg2]kyotorphin.

Bile salts and synthetic surfactants have been used to promote nasal absorption of peptide drugs. Although a marked increase in nasal absorption has been achieved, this may not be adequate and the possibility of adjuvant-induced membrane toxicity exists. The present study employs a rat in situ nasal perfusion technique and mixed micelles between sodium glycocholate (NaGC) and various lipids as potential nasal absorption enhancers of a stable model dipeptide, [D-Arg2]kyotorphin. NaGC alone enhanced the nasal absorption of the dipeptide in a concentration-dependent manner. When linoleic acid was added to form mixed micelles with NaGC, the absorption was further enhanced (P less than 0.01). The effect of mixed micelles was synergistic and much greater than with single adjuvants. Increasing ionic strength was found to increase the adjuvant activity of both NaGC and NaGC-lipid mixed micelles. Structure of the lipid component of the mixed micelles also affected the adjuvant potency. Oleic acid, a cis-unsaturated fatty acid, was more effective than elaidic acid, the trans-isomer, whereas cis-linoleic acid and trans-linolelaidic acid were equally effective (alpha = 0.05). Mixed micelles of mono-glycerides such as monoolein and monolinolein were also more effective than NaGC alone (alpha = 0.05). Micellar solubilization of these polar lipids by NaGC appears to be important for nasal absorption enhancement to occur. Reversal of the membrane permeability was also observed within approximately 20-40 min after removal of the adjuvants from the rat nasal cavity. These observations are similar to the effects of mixed micelles on the rectal mucosa and may involve the same mechanism.

Adjuvants, Pharmaceutic↗
PubMed1982

Maternal essential fatty acid supplementation increases zinc absorption in neonatal rats: relevance to the defect in zinc absorption in acrodermatitis enteropathica.

Pregnant zinc deficient and zinc adequate rats were injected subcutaneously with evening primrose oil throughout gestation and for 3 days post partum. The nursing pups were injected intragastrically with zinc-65 on day 3 of live and sacrifices 4 h later. The % of the total injected zinc recovered in the carcass (minus the gut and gut contents) was significantly increased in those pups nursed by mothers injected with evening primrose oil, regardless of their dietary zinc intake. The fatty acid composition of the total lipid extract of the gut and gut contents of the neonates with increased zinc-65 absorption indicated that these pups had higher proportions of arachidonic acid and other metabolites of linoleic acid than did those with lower zinc-65 absorption. In other 3-day-old rat pups, intragastric injection of linoleic, gamma-linolenic or dihomo-gamma-linolenic acids along with the dose of zinc-65 very significantly increased zinc-65 absorption in a dose-related manner. Arachidonic acid however had no significant effect on zinc-65 absorption. Prostaglandin E1 caused a significant increase in zinc-65 absorption but prostaglandin E2 had no consistent effect. Indomethacin caused a dose-related inhibition of zinc-65 absorption.

Acrodermatitis↗
PubMed1985

[Comparative studies on the enzymatic absorption of protein hydrolysates in the small intestines of the rat. 3. The absorption of trypsin, thermitatic and trypsin thermitatic wheat gluten hydrolysates in comparison with equimolar mixtures of free amino acids].

Tryptic, thermitatic, and tryptic-thermitatic wheat-gluten hydrolyzates as well as their equimolar amino-acid mixture were perfused through proximal and distal parts of the intestine (10 cm length) of non-narcotized rats. The total amino-acid concentration of the perfused solution was 50 mM. The tryptic hydrolyzate showed a significantly lower absorption of nitrogen and total amino acids than the amino-acid mixture. Both the supplied forms were very different as to their absorption pattern of the amino acids. The high variability of the percental absorption of the individual amino acids of the tryptic hydrolyzate results in a high coefficient of variation. The absorption of nitrogen and total amino acids from thermitatic and tryptic-thermitatic hydrolyzates is equal to that from the amino-acid mixture. In a peptidic form glutamic acid is more rapidly absorbed from the two hydrolyzates, and methionine from the tryptic-thermitatic hydrolyzate in both the intestinal parts. As to alanine and glycine this concerns only the distal intestinal part for both the hydrolyzates. There are no differences between the absorption patterns of the two hydrolyzates but in comparison with the amino-acid mixture and the tryptic hydrolyzate differences were evident. The coefficients of variation of both the hydrolyzates are significantly lower as compared to those of the tryptic hydrolyzate and the amino-acid mixture. All forms of supply are more rapidly absorbed in the distal than in the proximal part of the intestine.

Amino Acids↗
PubMed1975

Percutaneous absorption of drugs. IV. Percutaneous absorption of drugs from oily vehicles.

The percutaneous absorption and retention of salicylic acid and carbinoxamine from four oily vehicles (liquid paraffin, oleic acid, hexadecyl alcohol, and isopropyl myristate) were studied by employing a recirculation apparatus. The absorption followed first-order kinetics, with the exception of the initial period. The vehicle that had a strong affinity to the drug showed a poor drug-releasing effect, and poor absorption and retention of drugs by the skin were observed. Higher absorption rate constants were observed for damaged skin than intact skin. The acceleration of absorption because of skin damage, however, was not so great from liquid paraffin as from the aqueous solution. The amount of drugs retained in the damaged skin declined following the initial increase.

Animals↗
PubMed1984

Physical model approach to gastrointestinal absorption of prostaglandins III: In situ rat intestinal absorption of dinoprostone.

In situ absorption studies with dinoprostone in the rat jejunum were carried out to provide a quantitative mechanistic insight of the absorption process. The variables included buffer pH (3.5-9.5), buffer capacity, hydro-dynamics in the lumen, and concentration. The disappearance kinetics from the lumen was first order. The rate decreased with increasing pH in a sigmoidal manner and reached a minimum at about pH 9. These results indicate the effects of the partitioning of nondissociated species in the lipoidal membrane and transport across aqueous pores. The rate was higher with the higher degree of agitation of the lumenal solution. Between two hydrodynamic situations, the differences in the rates were large at pH 4.5 where the transport was largely aqueous diffusion controlled and then tended to become smaller with increasing pH where the transport became effectively membrane controlled. The 15-oxo- and 13,14-dihydro-15-oxo metabolites of dinoprostone were found. The physical model was applied to quantify the permeability coefficients of the aqueous diffusion layer and the aqueous pores of the membrane and the effective membrane transport-bioconversion permeability coefficient at various pH values. The overall absorption dinoprostone was similar to that of the less lipophilic dinoprost reported earlier and also more rapid. Hence, baseline absorption studies were completed with two major reference prostaglandins from which estimations of intestinal absorption can be made for their analogues and derivatives.

Animals↗
PubMed1990

Solute absorption from the airways of the isolated rat lung. II. Effect of surfactants on absorption of fluorescein.

To determine the effects on the pulmonary barrier of several surface active agents, a series of metered dose inhalers (MDIs) was prepared and used to dose aerosolized surfactant to the airways of isolated perfused rat lungs. The MDIs contained a range of concentrations, from 0.1 to 5.0% (w/w), of either oleic acid, oleyl alcohol, or Span 85, which released approximately 45 micrograms (0.1%, w/w) to approximately 1660 micrograms (5.0%, w/w) of surfactant per actuation. The permeability of the pulmonary barrier was assessed by the rate of transfer of disodium fluorescein dosed as 100 microliters of aqueous solution (1 mg/ml) after administering the surfactants. Some 12.1 +/- 4.7% of the recovered surfactant, per dose, was assessed to reach the pulmonary regions of the lung. All surfactants tested caused an increase in fluorescein transfer rates. A single actuation from the MDI containing 5% (w/w) oleic acid produced gross edema in all lungs tested within 40 min and the first-order half-lives of absorption were reduced almost threefold, from 12.9 +/- 2.5 min for controls to 4.5 +/- 0.8 min. Differences in absorption were noted between the acid and the alcohol, which is consistent with the hypothesis that both the hydrocarbon chain and the polar head group have roles in the altered permeability to fluorescein. The absorption of fluorescein when dosed from the MDI containing 5% (w/w) Span 85 was increased but all surfactants dosed from the lowest concentration MDI of 0.1% (w/w) did not alter absorption rates of the dye relative to those of controls. Results are discussed in light of current interest in absorption enhancement and the presence of surfactants in currently marked MDIs.

Absorption↗
PubMed1990

Bile salt-fatty acid mixed micelles as nasal absorption promoters of peptides. II. In vivo nasal absorption of insulin in rats and effects of mixed micelles on the morphological integrity of the nasal mucosa.

The effectiveness of mixed micelles in promoting nasal absorption of peptides has been demonstrated in vivo by employing insulin as a model compound. Insulin in the absence of adjuvants was not absorbed following intranasal administration. The results confirmed previous findings by others that absorption of insulin via alternative routes required absorption enhancers. Mixed micelles between NaGC and linoleic acid were found to rapidly deliver insulin into systemic circulation, with a concomitant decrease in plasma glucose. The extent of the hypoglycemic response was significantly greater than that produced by NaGC alone (55 vs 47%, P less than 0.05). Emulsion of linoleic acid, on the other hand, did not produce any significant insulin absorption. The findings thus supported previous in situ data that mixed micelles were more effective than NaGC or linoleic acid in promoting nasal absorption of peptides. Histopathologic examination of the rat nasal mucosa revealed that the extent of morphological alterations caused by mixed micelles was of mild to moderate severity even after 5 hr of exposure. However, studies involving more frequent and prolonged exposures are necessary to assess the practicality of these adjuvants before any clinical application can be attempted.

Absorption↗