Search PubMed⌕ Search

Biomedical subjects

S K Chang

Publications and source records attributed to S K Chang.

65 records · Page 4Linked to original sources
PubMed1979

Accelerating effect of ascorbic acid on N-nitrosamine formation and nitrosation by oxyhyponitrite.

The reaction of nitrite ion with ascorbic acid and its effect on the rate of nitrosation of secondary amines have been investigated by differential pulse polarography in aqueous acidic solution. Ascorbic acid shows nonuniform behavior: it accelerates the nitrosation of N-methylaniline between pH 1.00 and 1.95, allows the nitrosation of diphenylamine and iminodiacetonitrile, but inhibits the nitrosation of secondary amines, such as dimethylamine, diethylamine, proline, hydroxyproline, N-methylaminoacetonitrile, N-methylaminopropionitrile, and sarcosine. The nitrosating agent generated by the reaction between ascorbic acid and nitrite ion appears to be oxyhyponitrite ion (N2O3-2).

Ascorbic Acid↗
PubMed1977

Platelet adhesion to solid surfaces. The effects of plasma proteins and substrate wettability.

Platelet adhesion tests were performed using protein-free washed pig platelet suspensions in conjunction with a simple open-static method on smooth, well-defined protein-coated glass and polymer surfaces and bare glass and polymer surfaces. A normalization technique was introduced in an attempt to correct day-to-day variations in platelet reactivity. Protein coatings reduced platelet adhesion (to glass as well as polymer surfaces) to such a low level that the platelet density on one protein/substrate combination could not be distinguished from that on any other protein/substrate combination. Specifically, albumin and fibrinogen behaved identically regardless of the substrate on which they were coated. The addition of albumin and gamma-globulin to the platelet-suspension also significantly reduced platelet adhesion to glass surfaces. Whereas the extent of platelet adhesion from protein-free suspensions to bare glass and polymer surfaces depended on their wettability, the presence of specific chemical groups in the proteins, such as (-CONH-), may have an overriding effect on platelet adhesion to solid surfaces.

Blood Proteins↗
PubMed1977

Inhibition of dimethylnitrosamine-induced strand breaks in liver DNA and liver cell necrosis by diethyldithiocarbamate.

Diethyldithiocarbamate (DEDTC) prevented dimethylnitrosamine (DMN)-induced strand breaks in liver DNA and liver cell necrosis in male Wistar rats. In contrast, DEDTC did not inhibit the fragmentation of liver DNA caused by several other chemical carcinogens (N-hydroxy-2-acetylaminofluorene, 3-hydroxyxanthine, aflatoxin B1, N-acetoxy-2-acetylaminofluorene, methyl methanesulfonate, methylnitrosourea, and methylazoxy-methanol acetate), whether or not they required metabolic activation. Aminoacetonitrile exerted an action similar to that of DEDTC. The inhibitory effect was transitory, lasting at least for 4 hours, and protection for longer than 4 hours required multiple administrations of DEDTC. DEDTC also inhibited the serum clearance of DMN, methylation of liver DNA, and oxidative demethylation of DMN in the in vitro hepatic microsomal system prepared from either male Wistar rats or from hamsters. Interference of the metabolism of DMN appeared to be the mechanism by which DEDTC arrested DMN-induced biochemical and biologic effects.

Aminoacetonitrile↗
PubMedDate not supplied

Active index for content-based medical image retrieval.

This paper introduces the active index for content-based medical image retrieval. The dynamic nature of the active index is its most important characteristic. With an active index, we can effectively and efficiently handle smart images that respond to accessing, probing and other actions. The main applications of the active index are to prefetch image and multimedia data, and to facilitate similarity retrieval. The experimental active index system is described.

Abstracting and Indexing↗
PubMedDate not supplied

The use of contrast-enhanced color Doppler ultrasound in the differentiation of retinal detachment from vitreous membrane.

OBJECTIVE: To compare the clinical utility of contrast-enhanced color Doppler US in the differentiation of retinal detachment (RD) from vitreous membrane (VM) with that of various conventional US modalities, and to analyze the enhancement patterns in cases showing an enhancement effect. MATERIALS AND METHODS: In 32 eyes examined over a recent two-year period, RD (n=14) and VM (n=18) were confirmed by surgery (n=28) or clinical follow-up (n=4). In all cases, gray-scale, color Doppler, and power Doppler US were performed prior to contrast injection, and after the intravenous injection of Levovist (Schering, Berlin) by hand for 30 seconds at a dose of 2.5 g and a concentration of 300 mg/mL via an antecubital vein, contrast-enhanced color Doppler US was performed. At Doppler US, the diagnostic criterion for RD and VM was whether or not color signals were visualized in membranous structures. RESULTS: Diagnostic accuracy was 78% at gray-scale US, 81% at color Doppler US, 59% at power Doppler US, and 97% at contrast-enhanced color Doppler US. The sensitivity of color Doppler US to color signals in RD increased from 57% to 93% after contrast enhancement. The enhancement patterns observed were signal accentuation (n=3), signal extension (n=2), signal addition (n=3), and new signal visualization (n=5). CONCLUSION: Contrast-enhanced color Doppler US was the most accurate US modality for differentiating RD from VM, showing a significantly increased signal detection rate in RD.

Adolescent↗