Search PubMed⌕ Search

Biomedical subjects

S Cheng

Publications and source records attributed to S Cheng.

At least 307 records · Page 17Linked to original sources
PubMed1982

Isocratic high-performance liquid chromatographic method for the determination of tricyclic antidepressants and metabolites in plasma.

An isocratic high-performance liquid chromatographic method for the determination of six tricyclic antidepressants and their major metabolites is presented. Hexane containing 0.5% diethylamine was used as an extraction solvent to minimize adsorption onto glass. A reversed-phase cyanopropylsilane column was used with a mobile phase consisting of 70% acetonitrile and 30% 0.03 M acetate buffer, pH 7.0. Good identification and quantitation were obtained by the use of both UV detection at 245 nm and spectrofluorometric detection with an excitation wavelength of 276 nm and an emission filter with a 370-nm cutoff. A minimum detectable limit of less than 5 ng/ml of plasma is possible with this system. The reproducibility and precision of the method are shown from the analysis of samples containing 20-400 ng/ml in plasma.

Adsorption↗
PubMed1982

Affinity labeling of the plasma membrane 3,3',5-triiodo-L-thyronine receptor in GH3 cells.

The binding of 3,3',5-triiodo-L-thyronine (T3) to GH3 rat pituitary tumor cells was studied at 15 degrees C and was shown to be saturable, reversible, and stereospecific. Least-squares analysis of the binding data showed two classes of binding sites with dissociation constants of 1.8 +/- 0.2 nM and 260 +/- 30 nM and binding capacities of (5.2 +/- 0.2) X 10(4) and (1.6 +/- 0.2) X 10(6) sites per cell, respectively. Affinity labeling of intact cells was carried out by incubation of cells with 0.3 nM N-bromoacetyl-[125I]T3 at 15 degrees C for 1 hr. Analysis of the cellular extracts by sodium dodecyl sulfate gel electrophoresis showed three labeled protein bands with apparent molecular masses of 55, 47, and 33 kilodaltons (kDal) in a ratio of 86:7:7. The labeling of only the 55-kDal protein band was selectively reduced to 50% by 20 microM unlabeled T3. Highly purified plasma membranes of GH3 cells were prepared and shown to be free of nuclei. Affinity labeling of the purified plasma membranes gave the same labeling pattern as with intact cells. Peptide mapping by Staphylococcus aureus V8 digestion of the 55-kDal protein from cells or plasma membranes gave the identical peptide fragments. Thus the 55-kDal protein labeled from intact cells is the same protein as that from purified plasma membranes. These results together with our earlier findings [Horiuchi, R., Cheng, S.-y., Willingham, M. & Pastan, I. (1982) J. Biol. Chem. 257, 3139-3144] suggest that the 55-kDal protein may be involved in mediating the uptake of T3 in GH3 cells.

Affinity Labels↗
PubMed1981

Sputum and plasma doxycycline concentrations after a single oral 600 mg doxycycline dose in patients with chronic bronchitis.

Plasma and sputum concentrations of doxycycline were measured in 10 patients with chronic bronchitis for a period of 96 h after a single oral 600 mg dose of doxycycline. The plasma doxycycline levels exceeded the minimal inhibitory concentrations (MIC) against common respiratory pathogens. Sputum doxycycline levels were detected in nine patients and these compared favourably with the above MICs for 24 h. The mean percent ratio of sputum/plasma doxycycline level reached a maximum of 28% at 48 h. There was a positive correlation between sputum and plasma doxycycline levels. This study provides pharmacokinetic support for a single oral 600 mg dose of doxycycline in the treatment of acute bronchial infection.

Aged↗
PubMed1979

Effect of deglycosylation on the binding and immunoreactivity of human thyroxine-binding globulin.

Thyroxine-binding globulin (TBG), prepared from human serum by an improved purification method, was treated with a mixture of neuraminidase, beta-galactosidase, alpha-mannosidase, and beta-N-aectylglucosaminidase, which resulted in the removal of approximately 86% of saccharides. Purification by thyroxine-Sepharose affinity chromatography gave a homogeneous protein as shown by equilibrium sedimentation and sodium dodecylsulfate-polyacrylamide gel electrophoresis. Amino acid and NH2-terminal sequence analysis indicated that the protein moiety was intact. Deglycosylation had no effect on the stoichiometry of the binding of L-thyroxine as shown by tryptophanyl fluorescence quenching and equilibrium dialysis at pH 8.6 and 25 degrees C. However, the affinity constant for L-thyroxine was reduced from 1.6 X 10(9) M-1 to 0.58 X 10(9) M-1. Analysis of radioimmunoassay data revealed that deglycosylation resulted in a slight decrease of the affinity constant for anti-TBG antibody from 3.9 X 10(10) M-1 to 1.8 X 10(10) M-1. These results suggest that the polypeptide moiety, rather than the heterosaccharides, contains the antigenic determinants. Removal of the majority of the heterosaccharides of TBG has only a minor effect on its immunoreactivity and on the binding of thyroid hormone.

Amino Acids↗
PubMed1979

Pharmacokinetics and tolerability of a single oral 600-mg dose of doxycycline.

The pharmacokinetics of a single orally administered 600-mg dose of doxycycline (six 100-mg film-coated tablets) was studied in 18 healthy subjects. Plasma doxycycline levels remained above 1.35 mumol/L for 48 hours and compared favourably with the mean inhibitory concentrations of doxycycline against the common infecting organisms in chronic bronchitis. In a separate tolerability study in 37 healthy subjects, there was no significant difference between doxycycline and placebo in the incidence of adverse effects.

Adult↗