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S Yoshioka

Publications and source records attributed to S Yoshioka.

At least 235 records · Page 13Linked to original sources
PubMed1987

Limits to the concept of solid-state stability.

Recently published data about the decomposition of propantheline bromide in the presence of moisture resulted in a general, two-variable, phenomological equation relating the decomposition to the relative humidity and temperature. The true curve, however, is biphasic, since complete liquefaction occurs at some time point. This article deals with the development of a theoretical equation relating decomposition time, temperature, and relative humidity during the solid-state stage (i.e., during the period when solid is still present in the system).

Drug Stability↗
PubMed1987

Statistical evaluation of nonisothermal prediction of drug stability.

Nonisothermal prediction of drug stability based on direct nonlinear estimation of the shelf-life was compared with the isothermal approach. The reliability of the statistics for the estimates of the shelf-life (the time period required for a drug to degrade to 90% remaining at 25 degrees C) and activation energy obtained by the two methods was evaluated by the Monte Carlo method of computer simulations. The accuracy and precision of the estimates obtained by the nonisothermal method depended largely on the experimental conditions, such as experimental periods, sampling time, and temperature rise programs. The uncertainty of the estimates was determined mainly by the extents of drug degradation and temperature change achieved during the experiment. The nonisothermal method needed suitable experimental designs and precise assay methods of drug contents to provide reliable parameter estimates.

Computers↗
PubMed1987

Kinetics of hydrolysis of meclofenoxate hydrochloride in human plasma.

The kinetics of hydrolysis of meclofenoxate hydrochloride in human plasma have been compared with those of clofibrate. The hydrolysis rate in fractionated plasma was determined in the presence and absence of a plasma esterase inhibitor, tetraethyl pyrophosphate. The kinetic data indicated that clofibrate decomposed only by esterase-induced hydrolysis, which was inhibited by binding of clofibrate to plasma proteins. In contrast to clofibrate, meclofenoxate decomposed rapidly in human plasma via spontaneous hydrolysis as well as esterase-induced hydrolysis. The spontaneous hydrolysis appeared to be inhibited by some components present in the esterase fraction isolated from plasma, while no significant inhibition of the hydrolysis by protein binding was observed.

Blood Proteins↗
PubMed1986

Inositol 1,4,5-trisphosphate-induced Ca2+ release from permeabilized mastocytoma cells.

The effect of inositol 1,4,5-trisphosphate (IP3) on Ca2+ release in the transformed murine mast cells, mastocytoma P-815 cells permeabilized with digitonin was studied. Ca2+ was sequestered by intracellular organelles in the presence of ATP until the medium free Ca2+ concentration was lowered to a new steady-state level. The subsequent addition of IP3 caused a rapid Ca2+ release, which was followed by a slow re-uptake of Ca2+. Fifty percent of the sequestered Ca2+ was released by 10 microM IP3. Maximal Ca2+ release occurred at 10 microM and half maximal activity was at 1.3 microM. These results indicate that IP3 may function as a messenger of intracellular Ca2+ mobilization in mastocytoma cells.

Adenosine Triphosphate↗
PubMed1986

Kinetics and mechanism of the solid-state decomposition of propantheline bromide.

The kinetics of the solid-state hydrolysis of propantheline bromide (1) was studied with respect to the effect of temperature and water vapor pressure on the decomposition rate. For the hydrolysis at a relative humidity (RH) above the critical relative humidity (CRH), the percent decomposed (x) could be described by the empirical equation: x = ktn, where n is a constant independent of temperature and water vapor pressure, and k is related to temperature (T) and water vapor pressure (P) by the equation: k = k'e-Ea/RTPs (k' and s are constants). A mechanism in which the decomposition products serve to provide reaction nuclei is proposed. On the other hand, the hydrolysis at RH below the CRH could be described by a zero-order kinetic model with a lag time, and the dependence of the zero-order rate constant and the lag time on T and P was determined. The kinetic data suggested that decomposition occurs in an adsorbed moisture layer.

Adsorption↗
PubMed1986

Nonlinear estimation of kinetic parameters for solid-state hydrolysis of water-soluble drugs.

Nonlinear-regression analysis was applied to estimate the kinetic parameters for the solid-state hydrolysis of meclofenoxate hydrochloride [2-(dimethylamino)ethyl (4-chlorophenoxy)acetate hydrochloride; 1] and propantheline bromide [(2-hydroxyethyl)diisopropylmethylammonium bromide xanthene-9-carboxylate; 2]. The percent decomposed (x) at the initial stage of decomposition was found to conform to the empirical equation x = ktn, where n and k are constants. The goodness of fit of the data was better than with the Prout-Tompkins equation. The parameters indicating the dependence of the rate on temperature (T) and water vapor pressure (P) were estimated by nonlinear-regression analysis based on the equation: x = x0 exp[(Ea/R)(1/298-1/T)] (P/18.167)s(t/50)n, where xo is the percent decomposed at t = 50 d, T = 298 K and P = 18.167 mmHg, and Ea (activation energy), s, and n are constants. For the hydrolysis at a relative humidity (RH) above the critical relative humidity (CRH), nonlinear parameter estimation provided statistically meaningful estimates of Ea, s, x0, and n, and it was suggested that these parameters could be regarded as constants in the experimental range. For the hydrolysis at RH below the CRH, however, the parameters could not be converged by nonlinear-regression analysis, and Ea and/or s were assumed not to be constant in this RH range.

Chromatography, High Pressure Liquid↗
PubMed1986

2-Deoxy-2-[18F]fluoro-D-galactose: a new tracer for the measurement of galactose metabolism in the liver by positron emission tomography.

We prepared 2-deoxy-2-[18F]fluoro-D-galactose as a potential radiopharmaceutical for liver imaging and for the assessment by positron emission tomography of regional metabolic function of the liver. In biodistribution studies of rats, the liver uptake of the compound was very high, almost reaching a plateau (6.33% dose/g) at 30 min and remaining constant until 120 min. This high uptake was reduced by simultaneous administration of D-galactose, but D-glucose had no effect. The compound was much less concentrated in the liver that had been damaged by CCl4 treatment. Positron imaging of a rabbit liver showed a remarkable uptake of the compound with a high liver-to-blood ratio. The high concentration in the liver was also reduced by the administration of D-galactose. These data suggest that the compound was trapped in the liver by a metabolic process and could be used for the measurement by positron emission tomography of galactose metabolism in the liver.

Animals↗