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Biomedical subjects

Q Feng

Publications and source records attributed to Q Feng.

At least 91 records · Page 5Linked to original sources
PubMed1995

[Percutaneous absorption of venenum bufonis in vitro].

V-C horizontal diffusion cell and HPLC determination have been used to study the effect of 1,2-propanediol and azone on the percutaneous absorption Venenum Bufonis. The contents of resibufogenin have been determined through mouse skin in vitro by HPLC. The results indicate that the contents get increased when 1,2-propanediol is added and that azone can shorten the lag time of percutaneous absorption of resibufogenin through mouse skin in vitro.

Amphibian Venoms↗
PubMed1995

[A modified esophagogastrostomy: report of 528 patients].

The nearby tissues were used to cover the esophagogastric anastomotic stoma in 528 patients with esophageal and cardiac cancer undergoing resection. After interrupted suturing of the whole layer of esophagus and stomach, the paracervicalis was anastomosed with the capsule of the thyroid gland to strengthen the anterior wall of the anastomotic stoma. In case the anastomosis is done alove the arch of aorta, a flap of pedicled plewa is produced to cover the upper frigonum. The lower ligamentum pulmonale was used to coner the anastomosis when it is performed subaoticolly. No anastomotic leakage and stenosis were found in 528 patients in the follow-up of 2-5 years.

Adult↗
PubMed1995

[Experimental analysis of the calcium source for cardiac excitation-contraction coupling in hibernator Citellus dauricus].

The force-interval and force-frequency relationships and the effects of Cd2+ and ryanodine on the myocardial action potential and contraction were compared between hibernating (HGS) and active (AGS) ground squirrels Citellus dauricus. (1) Raising the driving frequency caused a negative inotropic effect in the AGS group, but a biphasic change with an increase of the peak force followed by a decrease in the HGS group. The contraction in HGS group exhibited a more pronounced post-interval potentiation, and was more significantly modulated by the driving frequency. (2) HGS animals displaged action potentials of shorter early-stage duration and stronger contractions of shorter time course in comparison with the AGS animals. Both the action potential and the contraction of HGS group were less affected by Cd2+, but the contraction was more significantly inhibited by ryanodine than that of the AGS group. Our results suggested that dependence of cardiac excitation-contraction coupling on calcium influx was weakened, while the function of sarcoplasmic reticulum as a source of activator Ca2+ was enhanced during hibernation, which might take an important part in the cold-tolerant adaptation of hibernating hearts.

Action Potentials↗
PubMed1994

pH-induced conformational transitions of Cry IA(a), Cry IA(c), and Cry IIIA delta-endotoxins in Bacillus thuringiensis.

Three protoxins and corresponding delta-endotoxins from Bacillus thuringiensis (BT) were studied by means of circular dichroism spectroscopy and size-exclusion HPLC. At neutral pH, the Cry IIIA toxin exists only as a 65-kDa monomer. The toxins of Cry IA(a) and Cry IA(c) exist both as 66-kDa monomers and as oligomers with apparent molecular masses greater than 220 kDa. At neutral pH, interconversion between monomer and oligomer is slow, and the two, separate forms exist for several days. Equilibration between the monomer and oligomer in both Cry IA(a) and Cry IA(c) toxins is facilitated by increasing the pH of the solutions to above 10. The relative amounts of monomer and oligomer depend upon temperature, pH, and buffer composition. CD spectra of the protoxins and toxins indicate a large helix content. The CD spectra of HPLC-isolated, monomeric Cry IA(a) and Cry IA(c) are quite similar, but are different from the spectrum of Cry IIIA. The Cry IA(a) and Cry IA(c) protoxins exhibit more helical CD spectra than the corresponding toxins. The CD spectra, with the pH titration of Cry IA(a), reveal that there is a significant increase in helical content as the pH is changed from neutral to alkaline values, but no decrease at low pH. A similar titration of Cry IIIA revealed no significant change in structure from pH 6 to pH 11. The CD spectrum of Cry IIIA at pH 2 indicates that the helical content of the toxin has significantly decreased. The magnitude of the 222-nm signal decreases from pH 7 to 2, with a midpoint of approximately pH 4.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

An in vivo assay for the reverse transcriptase of human retrotransposon L1 in Saccharomyces cerevisiae.

L1 elements constitute a highly repetitive human DNA family (50,000 to 100,000 copies) lacking long terminal repeats and ending in a poly(A) tail. Some L1 elements are capable of retrotransposition in the human genome (Kazazian, H. H., Jr., C. Wong, H. Youssoufian, A. F. Scott, D. G. Phillips, and S.E. Antonarakis, Nature (London) 332:164-166, 1988). Although most are 5' truncated, a consensus sequence of complete L1 elements is 6 kb long and contains two open reading frames (ORFs) (Scott, A. F., B. J. Schmeckpeper, M. Abdelrazik, C. T. Comey, B. O'Hara, J. P. Rossiter, T. Cooley, P. Health, K. D. Smith, and L. Margolet, Genomics 1:113-125, 1987). The protein encoded by ORF2 has reverse transcriptase (RT) activity in vitro (Mathias, S. L., A. F. Scott, H. H. Kazazian, Jr., J. D. Boeke, and A. Gabriel, Science 254:1808-1810, 1991). Because L1 elements are so numerous, efficient methods for identifying active copies are required. We have developed a simple in vivo assay for the activity of L1 RT based on the system developed by Derr et al. (Derr, L. K., J. N. Strathern, and D. J. Garfinkel, Cell 67:355-364, 1991) for yeast HIS3 pseudogene formation. L1 ORF2 displays an in vivo RT activity similar to that of yeast Ty1 RT in this system and generates pseudogenes with unusual structures. Like the HIS3 pseudogenes whose formation depends on Ty1 RT, the HIS3 pseudogenes generated by L1 RT are joined to Ty1 sequences and often are part of complex arrays of Ty1 elements, multiple HIS3 pseudogenes, and hybrid Ty1/L1 elements. These pseudogenes differ from those previously described in that there are base pairs of unknown origin inserted at several of the junctions. In two of three HIS3 pseudogenes studied, the L1 RT appears to have jumped from the 5' end of a Ty1/L1 transcript to the poly(A) tract of the HIS3 RNA.

Base Sequence↗
PubMed1994

Secretion of plasminogen activator inhibitor type 1 by cultured ovarian cells obtained from gonadotropin-treated immature rats.

It is demonstrated that i) theca-interstitial compartment synthesizes the majority of plasminogen activator inhibitor type 1 (PAI-1) in the ovary before ovulation, and the follicular wall may therefore serve as a specific barrier with the presence of PAI-1 activity to prevent the secretion of tPA into the extrafollicular compartments; ii) granulosa cells secrete only a small amount of ovarian PAI-1, but synthesize the most of tissue-type plasminogen activator tPA involved in the processes leading to ovulation; iii) since only matured cumulus-oocyte complexes secrete a large amount of tPA and PAI-1, both tPA and PAI-1 activity in the conditioned medium may be used as reliable markers for evaluating oocyte quality for in vitro fertilization.

Animals↗
PubMed1993

The possible involvement of tissue type plasminogen activator in luteolysis of rhesus monkey.

Changes of plasminogen activators (PA) during different stages of development of the corpus luteum, and their possible physiological role in luteolysis were studied in rhesus monkeys. It was demonstrated for the first time that monkey corpus luteal cells not only produce PA, but that the function of the corpus luteum is also closely related to the activity of this enzyme system. Generally, the life span for a corpus luteum in monkey is approximately 14-16 days, its demise beginning thereafter. In the present study, we found that urokinase in the corpus luteum is higher on day 5 and day 10 after human chorionic gonadotrophin injection, while the tissue type (t) PA is mainly produced on day 13 when luteolysis may take place. Progesterone production remained high on day 5 and day 10 and decreased dramatically from day 13, indicating the important role of tPA but not urokinase (u) PA in suppressing luteal function. When purified tPA (but not uPA) monoclonal antibody was added to luteal cell culture to neutralize endogenously produced tPA activity, progesterone production in the cells was increased significantly. Interestingly, prolactin alone was capable of increasing PA production by luteal cells; prolactin together with luteinizing hormone, however, had a synergistic luteotrophic effect.

Animals↗
PubMed1993

Ultrastructural study of moniliformin induced lesions of myocardium in rats and mice.

Effects of moniliformin on the ultrastructure of the myocardium of mice and rats were studied. Mice were given moniliformin orally at a dose of 29.46 mg.kg-1 the LD50. One h after dosing, lesions of the mitochondria of the myocardial cells were found which became more severe in 2 and 3 h. Ultrastructural lesions were also observed in the myofibrils and sarcolemma. Rats were given moniliformin orally at the dosage of 6 mg.kg-1 once daily for 56 d. Lesions of mitochondria and myofibrils were relatively mild. In the myocardiac specimens taken from the 21d post-toxin administration, lesions of the sarcolemma became more obvious. These moniliformin-induced lesions were similar to the ultrastructural changes in the myocardium of patients with Keshan disease. Our findings indicate that there may be a close and important relationship between moniliformin intoxication and Keshan disease.

Animals↗
PubMed1992

Crossover reactions between synthetic replicators yield active and inactive recombinants.

Self-replicating molecules can be synthesized through the covalent linkage of two complementary subunits to give a self-complementary structure. Complementarity refers to sizes, shapes, and the weak intermolecular forces involved in molecular recognition between the two subunits. In order to provide a model system for evolution at the molecular level, "crossover" or recombination experiments were staged with synthetic replicators. These reactions gave rise to new structural types. The ability (or inability) of the new recombinants to catalyze their own formation is shown to be a consequence of their molecular shapes.

Catalysis↗
PubMed1992

Inhibition of endothelin (ET-1) induced pressor responses by the endothelin (ETA) receptor antagonist FR139317 in the pithed rat.

The effects of the novel ETA receptor antagonist, FR 139317, on ET-1 induced blood pressure changes were studied in the pithed Sprague-Dawley rat. FR139317 in a dose of 0.025 mg/kg b.w. had no effect while 0.05-1 mg/kg b.w. dose dependently inhibited the pressor response to an i.v. bolus injection of ET6-1 (800 pmoles/kg). While FR139317 potently inhibited the magnitide and duration of the ET-1 induced pressor response, the ETA antagonist did not significantly influence the shortlasting initial depressor response. We conclude that FR139317 in the pithed rat potently inhibits ET-1 mediated pressor responses and that this agent may become a significant tool to elucidate the putative physiological and pathophysiological role of ETA receptor mediated responses.

Animals↗
PubMed1992

[Plasminogen activators and plasminogen activator inhibitor type-1 in human endometrium].

Two types of plasminogen activator (PAs) are present in human endometrium, and their contents vary with the different phases of menstrual cycle, i.e. high in the proliferative phase and low in the secretory phase. In the present study by immunohistochemical technique, both uPA and tPA antigens were demonstrated in the stromal and glandular cells of the endometrium. In cell culture, tPA was released only from stromal cells and uPA only from glandular cells as determined by SDS-PAGE followed by fibrin overlay technique, but PA inhibitor type-1 (PAI-1) was secreted by both stromal and glandular cells. Furthermore, secretion of PAs from endometrial cells was enhanced by adding estradiol and markedly inhibited by progesterone in a dose dependent manner, while the PAI reacted just in the opposite way. The effect of the peptide hormones, hCG, GnRH, PRL, as well as cAMP in cell culture on the secretion of PAs and PAI was similar to that of estradiol, while forskolin demonstrated definitely more stimulative effect on tPA than uPA. Taking into account of the finding of the present study, it appears that, under hormonal control, a balance between PAs and PAI in the endometrium exists. The physiological roles of the PAs and PAI in the endometrium were discussed.

Adult↗