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Biomedical subjects

W I Higuchi

Publications and source records attributed to W I Higuchi.

At least 163 records · Page 9Linked to original sources
PubMed1977

Dissolution kinetics of cholesterol in simulated bile I: Influence of bile acid type and concentration, bile acid-lecithin ration, and added electrolyte.

A physical model approach was utilized to investigate cholesterol monohydrate dissolution kinetics in simulated bile. The static pellet method and the Berthoud theory were employed to assess the contributions of the diffusion-convection mass transfer resistance and those of the interfacial resistance to the overall kinetics. For almost all situations studied, the interfacial resistance was the dominant rate-determining factor. The effects of four bile acids and their concentrations, the bile acid-lecithin ratio, and the added electrolytes and their concentrations on the interfacial resistance were examined. The results were correlated with those obtained with human bile samples, and the indications were that the kinetics of cholesterol dissolution in bile may be explainable on the basis of the principal bile acids, lecithin, and the electrolytes in the bile.

Bile↗
PubMed1977

Dissolution rates of model gallstones in human and animal biles and importance of interfacial resistance.

Cholesterol monohydrate dissolution kinetics in human gallbladder bile were studied to determine the magnitudes of the in vitro dissolution rates, the rate resistances in human gallbladder bile, and the extent that the interfacial resistance is the rate-determining factor. Dissolution rate studies also were conducted using human duodenal bile and animal bile for comparison. The dissolution rate resistance, R, ranged from 10(4) sec/cm for chicken bile to 10(4)-10(6) sec/cm for human bile. Interfacial resistance was the rate-determining factor for essentially all results. Where chemical composition data were obtained, the R values for the human bile samples were consistent with predictions made from the simulated bile studies. In two human gallbladder specimens having low bile acid-lecithin molar ratios (i.e., 2.9 and 2.3), very high R values of 1.9 X 10(5) and 4.1 X 10(5) sec/cm were found. These values were in good agreement with the findings in the simulated bile studies and suggest that stone dissolution in patients with low bile acid-lecithin ratios may proceed very slowly, even when the bile is highly undersaturated with respect to cholesterol.

Animals↗
PubMed1977

Cholesterol gallstone dissolution rate accelerators I: Exploratory investigations.

Various compounds that might function as cholesterol gallstone dissolution accelerators were studied. The dissolution rates of cholesterol monohydrate pellets in synthetic bile (116 mM sodium cholate-32 mM lecithin) containing the agent at various concentration levels were determined. In the absence of any dissolution rate accelerator, the dissolution kinetics for cholesterol previously were found to be interfacial resistance controlled, and the rates were around 20 times less than the diffusion-controlled rates in the present experiments. Primary, secondary, and tertiary amines and quaternary ammonium compounds were effective accelerators. When the alkyl chain lengths were long enough and/or when the agent concentrations were high enough, the dissolution rates generally approached diffusion-controlled rates. Steroidal amines generally had good activity. Anionic and nonionic surfactants had little or negative activity.

Amines↗
PubMed1977

Skin as an active metabolizing barrier I: Theoretical analysis of topical bioavailability.

A model and explicit equations were developed to be used in the experimental design and data evaluation of situations where simultaneous metabolism and transport of drugs occur in the skin. By treating the skin as a two-ply laminate composed of the stratum corneum and the viable epidermis, which contains most of the catabolic enzymes that might render a drug inactive by metabolism, equations were developed permitting the in vitro assessment of factors that may affect topical bioavailability in vivo. Two situations were investigated. In the first, the drug was placed on the dermis side of the diffusion cell and did not penerate the stratum corneum. In the second, the drug, placed on the epidermis side, penetrated the stratum corneum and then passed through the metabolizing epidermis. Expressions for determining the metabolic rate constant from experimental data along with concentration profiles and flux expressions are given both for the drug and its metabolite.

Administration, Topical↗
PubMed1977

Synchronized crystal dissolution behavior for tooth enamel and synthetic (NBS) hydroxyapatite.

The synchronized cyrstal dissolution hypothesis previously proposed to explain the unusual dissolution behavior of human dental enamel and hydroxyapatite in partially saturated acidic media has been critically examined with dissolution-dialysis transport experiments. The findings are in accord with the hypothesis. A model based upon a variable effective solubility for the hydroxyapatite crystal is proposed.

Chemical Phenomena↗
PubMed1977

Unusual dissolution behavior of tooth enamel and synthetic HAP crystals under high partial saturation conditions.

The dissolution behavior of enamel and synthetic hydroxyapatite in acidic media possessing a high degree of partial saturation was found to be neither simple surface dissolution nor linear with time. Instead, a repetitive, stepwise dissolution pattern was observed. To explain this phenomenon, a model based upon a hypothesis that the crystals dissolve in a synchronized fashion was proposed.

Buffers↗
PubMed1976

Oil-water distribution of p-alkylpyridines.

The distribution of a homologous series of p-alkylpyridines between water and six organic solvents with varying degrees of polarity was investigated. The distribution coefficients were considered as reflections of the strength of net interactions involved in the solvents. The order was chloroform greater than octanol greater than carbon tetrachloride greater than butyl ether greater than hexadecane greater than octane. The effect of the methylene group upon the distribution coefficients differed little among the six solvents. The relative constancy was attributed to the predominance of the dispersion forces in the incremental effect.

Hydrogen-Ion Concentration↗
PubMed1976

Dissolution rates of high energy sulfathiazole--povidone coprecipitates II: characterization of form of drug controlling its dissolution rate via solubility studies.

Solubility studies were made to characterize the form of sulfathiazole controlling the rate of dissolution exhibited in previously reported dissolution rate studies of sulfathiazole coprecipitated with povidone. The aqueous solubility of the high energy form of sulfathiazole obtained using sulfathiazole--povidone coprecipitates was determined in the presence of polymer in solution. Its aqueous solubility in the absence of polymer was determined by extrapolation. The solubility value was much greater than either the supercooled melt or the crystalline forms of sulfathiazole. Stabilization of these sulfathiazole solutions supersaturated with respect to the more stable crystalline form was achieved by the addition of sufficient polymer to the solution to prevent nucleation of the crystalline form. The concentration of polymer required to prevent nucleation of the crystalline forms was much higher than the previously reported concentrations required to inhibit crystal growth of sulfathiazole. The ratio of the solubility value obtained for the coprecipitated sulfathiazole as compared with its crystalline form I was in agreement with the ratio of their dissolution rates obtained the plateau regions of the dissolution rate experiments reported previously. The extrapolated aqueous solubility values in the absence of povidone were obtained as a function of temperature and were utilized to obtain thermodynamic parameters. The difference in the heat of solution of the two forms of sulfathiazole from the slope of the van't Hoff plots of the extrapolated solubility values was 1618 cal/mole, in excellent agreement with the literature value. The free energy, enthalpy, and entropy at 27 degrees for the coprecipitated drug relative to its crystalline form I were 1125 cal/mole, 8439 cal/mole, and 24 eu, respectively, indicating the high degree of molecular randomness and lack of structure in these high energy systems. These results provide strong evidence for the presence of an amorphous state of sulfathiazole as the controlling phase of both the solubility and dissolution rate experiments involving the high energy form of sulfathiazole obtained by coprecipitation with povidone.

Crystallization↗
PubMed1976

Dissolution rate studies of cholesterol monohydrate in bile acid-lecithin solutions using the rotatingdisk method.

A physical model approach was used to investigate cholesterol gallstone dissolution kinetics in simulated bile. Critical experimental and theoretical investigations simulating in vivo conditions showed that, in the bile acid-lecithin solutions, there is a significant interfacial barrier for both cholesterol gallstone and cholesterol monohydrate pellet dissolution. In the present study, the rotating-disk dissolution method and the accompanying Levich theory were applied to assess the contributions of the diffusion convection mass transfer resistance and of the interfacial barrier to the overall kinetics. Cholesterol dissolution rates in bile acid solutions were about 2-20 times slower than diffusion-controlled rates depending upon the degree of agitation. As found in previous studies, these rates in the presence of sufficient concentrations of dissolution accelerators approached the theoretical diffusion-convection-controlled rates. To account for the much slower dissolution rates in bile acid-lecithin solutions, two possible kinetic interpretations were investigated. The first is based upon slow crystal-micellar solution interfacial kinetics, and the second is based upon a slow rate of cholesterol solubilization in the aqueous diffusion layer. For the latter, an analytical mathematical solution was obtained.

Benzoates↗
PubMed1976

Systems approach to vaginal delivery of drugs II: In situ vaginal absorption of unbranched aliphatic alcohols.

The absorption of unbranched aliphatic alcohols in the rabbit vagina was studied using a perfusion method, and the absorption rates were found to be first order with respect to the drug concentration in the vagina from methanol to octanol. A physical model involving an aqueous diffusion layer in series with a membrane consisting of aqueous pores and lipoidal pathways was used for analyzing the data. The physically based parameters in the model were determined. An effective diffusion layer thickness ("unstirred layer") of around 0.035 cm was found. The increase in the permeability coefficient for the lipoidal pathway per methylene group was around 2.5 for this homologous series.

Absorption↗
PubMed1976

Systems approach to vaginal delivery of drugs III: Simulation studies interfacing steroid release from silicone matrix and vaginal absorption in rabbits.

A composite physical model involving the simultaneous receding boundary release of drug from a drug suspension-silicone polymer matrix system, diffusion across the aqueous layer, and passive transport across the vaginal membrane consisting of parallel lipoidal and aqueous pore pathways is described. Simulation studies with progesterone and hydrocortisone illustrate matrix release-limiting, membrane absorption, and aqueous diffusion layer-limiting cases when the cylindrical silicone delivery device is interfaced with the vaginal membrane of the rabbit.

Cell Membrane↗
PubMed1975

Systems approach to vaginal delivery of drugs I: development of in situ vaginal drug absorption procedure.

In the framework of the development of drug delivery systems for locally administered contraceptive drugs, a reliable method that can afford quantitative evaluation of drug absorption behavior was explored using the rabit doe. A system was constructed based upon perfusing the drug solution in the vaginal tract. For this purpose, a "rib-cage" type cell was constructed and surgically implanted in the rabbit prior to an experiment. The primary purpose of the present paper is to evaluate the method, including the surgical operation and the perfusion system. The absorption experiments were carried out using n-butanol-1minus 14C as the model solute to survey the reproducibility of the absorption behavior. Experiments were conducted with a number of rabbits on several successive days to determine the day-to-day and animal-to-animal variations. The drug disappearance in the reservoir followed first-order kinetics from which the apparent permeability coefficient was calculated. The results indicated that a set of experiments may be carried out on a single animal and that the method generally affords rather high precision.

Absorption↗
PubMed1975

Systems approach to study of solute transport across membranes using suspension cultures of mammalian cells III: steady-state diffusion models.

General physical models are derived for the diffusional transport of drugs across membranes of mammalian cells in culture suspension. These models represent different sets of possible physical processes taking place during the transport of a drug molecule. Once the diffusing species reaches the cell barrier, it may gain entrance to the cell kinetically by one of the principal quasisteady-state mechanisms, all of which assume the cell membrane to be an integral part of the total barrier.

Biological Transport↗
PubMed1975

Systems approach to study of solute transport across membranes using suspension cultures of mammalian cells IV: Uptake and release kinetics of sterols.

The kinetics of uptake and release of desmosterol, cholesterol, and beta-sitosterol by Burkitt lymphoma cells at 26 degrees, pH 7.3, and isoosmotic conditions were quantitatively and mechanistically interpreted. The data are in agreement with the model involving the passive transport of the unbound sterol across the rate-determining plasma membrane, with rapid distribution within the heterogeneous cell interior. Effective permeability (P-e) and partition (K-e) coefficients of the sterols were inversely proportional to the serum concentration in the external media due to sterol-serum binding. These results are consistent with the mechanism in which only the unbound solute in the external solution participates in the membrane transport process. At all serum levels, P-e and K-e increased with increasing sterol polarity: desmosterol greater than cholesterol greater than beta-sitosterol.

Animals↗
PubMed1975

Systems approach to study of solute transport across membranes using suspension cultures of mammalian cells V: Uptake and release kinetics of cardiac glycosides by Burkitt lymphoma cells.

Mass transport studies with three cardiac glycosides in the Burkitt lymphoma cell system have provided significant examples of the factorization and quantification of the influences of serum-drug binding, membrane-drug binding, cell interior binding, and intrinsic membrane permeability upon the uptake and release kinetics of drugs in living cell systems. All of the data from the glycosides are in agreement with the general physical model involving the rapid equilibration of the solute within the cell after permeation through the rate-determining plasma membrane barrier. The transport of digitoxin was influenced by membrane and serum binding and that of digoxin was influenced by membrane binding. There was no binding of ouabain to the plasma membrane and serum. The variables in the uptake and release kinetic studies at pH 7.3 included the use of viable and heat-inactivated cells, fetal bovine serum levels, and temperature.

Burkitt Lymphoma↗