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Biomedical subjects

S Zeng

Publications and source records attributed to S Zeng.

At least 91 records · Page 5Linked to original sources
PubMed1993

Sustainable agriculture and integrated pest management in China.

In developed countries, emphasis is being switched from high productivity through the use of high inputs to ecologically sustainable agriculture. In developing countries such as China priority must be given to increasing food production while simultaneously trying to optimize sustainability. Achievements in plant protection are being countered by continued evolution of the pest ecosystem, in part driven by application of pesticides or the introduction of new crop varieties. Future management of the agricultural ecosystem requires the development of a method of 'super-long-term' prediction to evaluate possible consequences of different strategies of plant protection. Crop plants with durable resistance to pests must be derived by conventional breeding or by using biotechnology and genetic engineering. Genetic vulnerability can also be reduced by techniques such as gene rotation and mixed cropping. Biological control of plant pests shows promise but requires ecological study of the relationships among crop, pest and natural enemy. Implementation of sustainable pest management will need training and education of farmers, extension workers and policy makers to deliver new information in the developing countries.

Agriculture↗
PubMed1993

Intravitreal pharmacokinetics of liposome-encapsulated amikacin in a rabbit model.

BACKGROUND: Intravitreal injection of antibiotics has become a standard therapy for bacterial endophthalmitis. The duration of effective antimicrobial levels in the vitreous after single injection, however, may not be long enough to get optimal response. The authors prepared liposome-encapsulated amikacin for prolonging the duration of intravitreal therapeutic concentrations and investigated the intravitreal pharmacokinetics of the liposomes and amikacin in phosphate buffer solution (PBS) as control. METHODS: The liposome-encapsulated amikacin was prepared by reverse-phase evaporation method. The intravitreal pharmacokinetics of the liposomes was compared with amikacin in PBS by fluorescence polarization immunoassay. Albino rabbits were randomly distributed into 12 groups. Rabbits in groups 1 to 6 and in groups I to VI (control groups) received an intravitreal injection of the liposome-encapsulated amikacin and amikacin in PBS, respectively. RESULTS: The encapsulation rate of amikacin was 91%. The time of 50% spontaneous degradation (half-life) of the liposomes in PBS (38 degrees C, pH 7.4) was 47.6 days, and the time of 50% release (half-life) of the drug from the liposomes in PBS was 84.8 hours. The vitreous amikacin concentrations in groups 1 to 6 were significantly greater (P < 0.05) than those in control groups I to VI in every time interval, except in groups 1 to 3 at 1 hour after injection. The difference was particularly obvious in the endophthalmitis groups. The clearance of encapsulated amikacin in vitreous appeared to be related to the state of blood-ocular barrier and to the structural integrity of vitreous. The distribution, the absorption, and the elimination of encapsulated amikacin in vitreous showed the first-order kinetics. CONCLUSION: The liposome-encapsulated amikacin prolonged half-life of the drug in vitreous. The results of the pharmacokinetic analysis suggested that in endophthalmitis, especially in severe cases, the liposomes may be preferable to conventional preparation.

Absorption↗
PubMed1992

Comparative investigation of disposition of 3,4-(methylenedioxy)methamphetamine (MDMA) in the rat and the mouse by a capillary gas chromatography-mass spectrometry assay based on perfluorotributylamine-enhanced ammonia positive ion chemical ionization.

A gas chromatography-mass spectrometry assay based on perfluorotributylamine-enhanced ammonia positive ion chemical ionization has been developed for MDMA and three of its primary metabolites in biological specimens; the assay is linear from 2 to 1000 ng ml-1. Quantitatively, more of an administered dose of 10 mg kg-1 MDMA was excreted by the mouse (72%) than by the rat (35%); most in both species was excreted in urine and within 24 h. The difference in per cent excretion is entirely due to proportionally greater excretion of the parent drug by the mouse. 4-Hydroxy-3-methoxymethamphetamine (HMM) is the major urinary metabolite in both species. HMM and another primary metabolite, 4-hydroxy-3-methoxyamphetamine (HMA), were excreted mainly as glucuronide and sulphate conjugates (> 85%).

3,4-Methylenedioxyamphetamine↗
PubMed1992

Metabolism of carotenoid analogs in humans.

Single oral doses (100 mumol) in peanut oil of 4,4'-dimethoxy-beta-carotene, ethyl beta-apo-8'-carotenoate, and beta-apo-8'-carotenal were administered to healthy adult male subjects (n = 4-6). Blood samples were taken frequently thereafter, and serum carotenoids and retinoids were analyzed by HPLC. The metabolism of the three analogs was very different; 4,4'-dimethoxy-beta-carotene was oxidized at the 4 and 4' positions but apparently not cleaved, whereas ethyl beta-apo-8'-carotenoate was not detectably metabolized, and beta-apo-8'-carotenal was extensively converted to its corresponding acid, alcohol, and fatty acyl ester and detectably converted to retinyl ester and possibly to two shorter beta-apocarotenals. Serum concentrations of endogenous retinoids and carotenoids, except as noted above, were not affected in any case. Kinetically, the maximum serum concentrations, areas under the curve, and mean sojourn times for the three analogs differed by 50-, 270-, and 5-fold, respectively. For any given analog, however, the fractional standard deviations for these parameters were only 0.2-0.5.

Administration, Oral↗
PubMed1992

Clinical value of lung scintigraphy with Tc-99m gluconate in distinguishing benign from malignant lung diseases.

One hundred patients were studied with three-phase lung scintigraphy with Tc-99m gluconate. The results showed that there were statistically significant differences between benign and malignant lung lesions in the intensity of accumulation, the blood supply index ratio, and the radioactive uptake ratio. However, no difference was observed between the benign lung lesions and the healthy lungs. Analysis of false negatives and false positives revealed that false negatives had something to do with the cell types of the malignancies, in addition to the relatively small size of the lesions; the false positives were mostly caused by acute inflammation, for which obstructive pneumonitis might be responsible in part. It is concluded that Tc-99m gluconate is tumor-avid and can be used as an agent for positive imaging of lung cancer, because quantitative parameters, blood supply index ratio, and radioactive uptake ratio are more objective in distinguishing malignant lung lesions from benign ones, and are of relatively higher sensitivity and specificity. Thus, lung scintigraphy with Tc-99m gluconate provides an efficient supplementary measure for differentiating between malignant and benign lung lesions.

Adenocarcinoma↗
PubMed1992

[The experimental studies of the effect of Forskolin on the lowering of intraocular pressure].

The effect of the domestic Forskolin on lowering the intraocular pressure (IOP) of rabbits was studied. The results showed that the Forskolin significantly lowered the normal IOP of rabbits and blocked the ocular hypertension induced by water load in rabbits (p < 0.01). The maximum decrease value of 2%, 1% and 0.5% of the Forskolin was 0.59. 0.36 and 0.19 kPa (1 kPa = 7.5 mmHg), which showed the noticeable dose-effect relationship. Topical ocular application of Forskolin lowered IOP in 1/2 hour, reached to a peak in 2-3 hours and remained significantly for 10 hours. The pupillary diameter did not change when IOP were reduced. Furthermore, the Forskolin had potent stimulative properties to adenylate cyclase (AC). The greater the ability of the Forskolin to stimulate AC, the stronger the effect of IOP lowering.

Adenylyl Cyclases↗
PubMed1991

Functional analysis of the CPS I upstream sequences with a cat assay.

Expression plasmids (pKCPS-CAT) containing carbamyl phosphate synthetase (CPS I) upstream sequences of different lengths were constructed, and the function and characteristics of the sequences were studied with the CAT assay. Results showed that the CPS I upstream sequences exerted highly tissue-specific control on CPS I gene expression, and the -113 approximately -38 bp region relative to the cap site was found to be indispensable for CPS I gene transcription. The -1700 approximately -161 bp region contains sequences which confer an enhancing effect on CPS I gene transcription. Dexamethasone and thioproline (a differentiation inducer) showed enhancing effects on CPS I gene transcription in hepatoma cells. These results would have significance in studies on the gene regulation of CPS I associated with the mechanism of hepatocyte differentiation and carcinogenesis.

Antineoplastic Agents↗
PubMed1990

A survey of children with HBsAg markers related to their parents HBV markers.

It was showed that 103 children with HBsAg markers alone (4-8 years of age) were closely selected to their either mothers or fathers. The data indicated that all of HBV markers were detected in all samples except. Three of them. But one of their three children was adopted. The ratio of HBsAg and HBeAg in the parent's positive sera was 26.6% to 12.5%. Even though the mother with HBeAg marker played an important role in the transmission of hepatitis B infection, but we could not omitted the role of father with HBeAg marker. Therefore some persistent appropriate measures in daily life was necessary to prevent children from HBV infection. Hepatitis B vaccine inoculation should be considered firstly on new born infants, nursery children and then those who were HBV markers negative.

Adult↗
PubMed1987

Menstrual blood loss and hematologic indices in healthy Chinese women.

Menstrual blood loss, cyanmethemoglobin and serum ferritin were determined in 421 healthy, noncontracepting Chinese women. The range of menstrual blood loss (MBL) was 4.1-273.6 mL, the mean value was 54.2 mL, and the median was 42.9 mL. The range of hemoglobin was 8.3-16.7 g/dL, and the mean value was 13.2 g/dL. The range of ferritin was 1.2-180.0 ng/mL, the mean value was 22.8 ng/mL, and the geometric mean was 17.1 ng/mL. The upper normal limit of MBL in Chinese women was set at 80 mL.

Adolescent↗
PubMed1986

Menstrual blood loss, haemoglobin and ferritin concentration of Beijing women wearing steel ring, VCu 200, and TCu 220c IUDs.

Menstrual blood loss (MBL), serum ferritin and whole blood cyanmethemoglobin were measured at pre- and 1, 3, 6, 12, 18 and 24th postinsertion cycles in 60 women wearing the Steel Ring, the Copper V (VCu 200) or the Copper T (TCu 220c). The MBL, incidence of menorrhagia and iron deficiency anemia were lower among users of the Steel Ring than among users of the Copper V and T. Anemia occurred later and the duration of menstruation was shorter with the Steel Ring than with the Copper T. There were no statistically significant differences between the Copper V and T.

Anemia↗
PubMed1985

[Evidence for the internalization and degradation of insulin in cultured Bri-7K human lymphocytes].

We have studied the internalization of insulin and the mechanism of insulin degradation in cultured Bri-7K human lymphocytes. The internalization of 125I-insulin was observed by using an acid extraction technique by Heigler's method which removed surface-bound insulin, leaving only intracellular insulin associated with cells. Insulin binding to Bri-7K cells reached a peak at 15 min and showed a gradual fall thereafter at 37 degrees C. Internalization of insulin rose with a peak in 30 min, and its rate was nearly 25% of the total specific cell-associated radioactivity. Insulin degrading activities in Bri-7K cells were examined as to precipitability with trichloroacetic acid (TCA method), Sephadex G-50 column chromatography (gel chromatography method) and the ability to bind to specific receptors on Bri-7K cells (rebinding method). Under conditions demonstrating that the insulin degradation didn't take place in the medium but was cell-mediated, the insulin degradation was not demonstrated by the TCA method. Chromatographic studies showed that the extractable radioactivity consisted almost entirely of intact insulin, whereas the supernatant and the nonextractable radioactivities consisted of large molecular weight material and intact insulin. Thus, the apparent degradation of insulin was not detectable by the TCA and gel chromatography methods, however, using the rebinding method, we could obtain results demonstrating that fair amounts of insulin in the supernatant were degraded. These results suggest that the products of insulin degradation are peptides with a molecular size similar to insulin itself but with little or no receptor binding activity. In conclusion, insulin internalizes into Bri-7K cells at physiological temperature, and the mechanism of insulin degradation in Bri-7K cells seems to be a limiting proteolysis of insulin by specific enzyme(s).

Cell Membrane↗
PubMedDate not supplied

Disposition of quercetin and kaempferol in human following an oral administration of Ginkgo biloba extract tablets.

Ten adult volunteers with an average age 28 years were given a single oral dose of six tablets of Ginkgo biloba extract. Quercetin and kaempferol in different period of human urine were determined by using RP-HPLC. The results showed the elimination rate constant k and the absorption rate constant ka of quercetin were slightly more than that of kaempferol; and the absorption half-life (t(1/2a)), the elimination half-life (t(1/2)) and t(max) of quercetin were less than that of kaempferol, the differences were, however, not statistically significant. The mean values of ka were 0.61 h(-1) and 0.55 h(-1), t(1/2a) 1.51 h and 1.56 h, k 0.37 h(-1) and 0.30 h(-1), t(1/2) 2.17 h and 2.76 h, T(max) 2.30 h and 2.68 h for quercetin and kaempferol, respectively, which mean absorption and elimination of quercetin and kaempferol are 0.17% and 0.22%, respectively. Quercetin and kaempferol are excreted in the human urine mainly as glucuronides.

Administration, Oral↗