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Biomedical subjects

M C Chen

Publications and source records attributed to M C Chen.

At least 127 records · Page 7Linked to original sources
PubMed1991

Clinical and electrophysiological assessment of cerebral malaria.

From January 1980 to December 1990, six cases of malaria were observed; three cases were caused by plasmodium (P.) vivax and three by P. falciparum. Following a malaria episode, two cases (33.3%), developed cerebral malaria. Both of them were infected by P. falciparum. Neurological and electrodiagnostic investigations were scheduled throughout their clinical course. The first case manifested as a grand mal seizure, followed by myoclonic jerk and a comatous state. A suppression burst EEG observed before anti-malarial therapy was initiated. In the second case, a manifestation of encephalo-myelo-neuropathy was confirmed clinically and electrophysiologically. Although both cases occurred suddenly and were extremely severe, early anti-malarial therapy resulted in good responses without sequelae. The complete reversibility of the pathological event depends on early recognition and comprehensive therapy. Further, electrophysiological assessment is recommended for the detection of regional involvement in cerebral malaria.

Adult↗
PubMed1990

Low probability of double integration in transformation of nonpermissive cells by polyomavirus.

The fate of polyomavirus genomes in stable transformants was examined in experiments in which rat or hamster cells were infected with mixed viral populations containing either two distinguishable wild types or a wild type plus a transformation-deficient mutant. The results demonstrate that in 90% of the cases in either situation, a single polyomavirus parental genome became integrated into the host genome. Both parents in the mixed infection were present in the same cells and both persisted in the infected cells until transformants appeared, eliminating the possibility that one virus would exclude the other in the early steps of the infection process. We believe that these results can be generalized to transformation events derived from normal single infections. Thus, contrary to previous results for the number of integration sites determined by restriction endonuclease and blot hybridization analysis, it appears that the probability for more than one integration event in transformation by polyomavirus is low (1 in 10). A reinterpretation of previous data is proposed.

Animals↗
PubMed1990

Inhibition of vasoconstriction by tetramethylpyrazine: does it act by blocking the voltage-dependent Ca channel?

Using dog mesenteric arterial ring preparations, we studied the in vitro vascular effects of tetramethylpyrazine (TMP, also known as Ligustrazine), a vasoactive component derived from Ligustium Wollichii Franchat; a widely used ingredient in Chinese herbal medicine for the treatment of cardiovascular diseases. TMP had no effect on the resting force of the vascular muscle, but it caused a dose-dependent inhibition of vascular contractile responses to KCl and phenylephrine (PHE). These inhibitory effects of TMP were reversible and more prominent at lower agonist concentrations. TMP also inhibited the responses to PHE in Ca-free medium containing 50 microM EGTA suggesting the action on the release of intracellular Ca2+. Therefore, TMP is not a specific Ca-channel blocker as claimed previously. Its vasodilatory effect is mediated by the inhibition of Ca influx, as well as the release of intracellular Ca2+.

Animals↗
PubMed1990

[Role of ventrolateral medulla in pressor response elicited by stimulation of abdominal vagi in cats].

The experiments were performed on 51 cats of either sex weighing 1.8-2.4 kg to investigate the role of the ventrolateral medulla in the pressor response elicited by stimulation of central ends of abdominal vagi. We observed that both the stimulation of the central ends of abdominal vagi and occlusion of one carotid artery increased the blood pressure by 17.4 +/- 1.6 mmHg (n = 51, P less than 0.01) and 14.7 +/- 1.9 mmHg (n = 19, P less than 0.01) respectively; blockade of the caudal ventrolateral medulla or trapezoid bodies with lidocaine had little effect on blood pressure and the pressor response, but blockade of the rostral ventrolateral medulla with either lidocaine or kainic acid could cause profound depression, and even abolition, of the pressor response. Moreover, application of atropine and phentolamine to the RVL severely inhibited the abdominal vagal pressor response without affecting the baroreceptor reflex. Taken together, we conclude that the RVL is a very important relay in the pathway of the abdominal vagal pressor response in which the adrenergic and cholinergic mechanisms may be involved in the RVL, and it seems that the pressor response pathway is independent of that of the baroreceptor reflex in the RVL.

Animals↗
PubMed1989

Oxygen metabolites modulate prostaglandin E2 production by isolated gastric mucosal cells.

We previously found that the small cell fraction of isolated cells from canine gastric mucosa is a major producer of prostaglandin E2 (PGE2) and identified macrophages as the predominant cellular source. Prostaglandin-H synthase activity is dependent on the continuous presence of hydroperoxides. Because reactive oxygen metabolites may mediate mucosal injury in inflammatory or ischemic disease, we studied the release of PGE2 by isolated gastric cells during exposure to an oxygen metabolite-generating system, xanthine and xanthine oxidase. We found a concentration-dependent relationship between xanthine oxidase concentration and PGE2 production without cell lysis. The maximum PGE2 production stimulated by oxidants was equivalent to the maximum PGE2 response to bradykinin and A23187. The chief and parietal cell fractions produced very little PGE2 with xanthine oxidase concentrations that stimulated maximal PGE2 production in the small cell fraction. Uric acid did not stimulate PGE2 production. Catalase completely inhibited the response, while superoxide dismutase had a partial inhibitory effect. Hydrogen peroxide stimulated concentration-dependent PGE2 production with an ED50 of approximately 5 microM. We concluded that reactive oxygen metabolites stimulate PGE2 production by the small cell fraction of gastric mucosa.

Animals↗
PubMed1989

Prostaglandin E2 production by dispersed canine fundic mucosal cells. Contribution of macrophages and endothelial cells as major sources.

Endogenous prostaglandins (PGs) influence resistance of the gastric mucosa to injury, but the source of PGs is unknown. Using radioimmunoassay, we studied PG production by dispersed canine fundic mucosal cells. PGE2 production, stimulated by bradykinin, epidermal growth factor, zymosan, and calcium ionophore, was greater in the small-cell elutriator fraction (SCEF) than in the medium and large cell fractions, which contained mucous, chief, and parietal cells. Linear density gradients of SCEF cells revealed maximal PGE2 production in cells of light density. Mast, endocrine, and endothelial cells did not account for this PGE2 production. Macrophages, identified by uptake of acetylated-LDL, immunoreactivity with antibodies to the human Ia antigen, and phagocytosis of fluorescent latex particles, were enriched in the SCEF and correlated with PGE2 production in the density gradient. Magnetic separation of cells in the SCEF-ingesting iron particles enriched PGE2 production. Fractions enriched in endothelial cells present in intact capillary fragments, but depleted of macrophages, also produced PGE2. Regulation of PGE2 production differed among cell types. Fibroblasts were easily cultured from submucosa, but were not detected in the SCEF. We conclude that macrophages and capillary endothelial cells are major producers of PGE2 in the canine fundic mucosa.

Animals↗
PubMed1989

[Is synchronous hemorrhoidectomy with colonoscopy a worthwhile procedure?].

There were 201 patients receiving preoperative colonoscopy prior to hemorrhoidectomy in the meanwhile at MMH from July 1984 to June 1988. Other than rectal bleeding, they had colonic symptoms such as anemia, abdominal pain, familiar history of cancer and change of bowel habit etc. The study included 114 male and 87 female with ages ranging from 15 to 74 years (Median, 42 years). Three patients with colonic cancer and twenty-eight patients with neoplastic polyps were found by colonoscopic examination. Three cancer patients all received cancer surgery instead of hemorrhoidectomy as quickly as possible in a short time. One patient died for advanced stage and the other two patients got good results. The literatures were reviewed and discussed in accordance with the colonoscopic finding, operative time, hospital stay, post-operative morbidity and complication. There were not increase the postoperative morbidity in this series which compare with that of other series. The advantages of this procedure included: 1) Preventing suffer from twice colon preparations. 2) Preventing waiting period for Barium enema. 3) Preventing delay diagnosis of colorectal lesions especially colon cancer or precancer lesions of neoplastic polyps. 4) Performing examination and surgery at the same time-money-saving and time-saving. We thought synchronous hemorrhoidectomy with colonoscopy is a worthwhile clinical procedure.

Adolescent↗
PubMed1988

Prostanoid inhibition of canine parietal cells: mediation by the inhibitory guanosine triphosphate-binding protein of adenylate cyclase.

We have investigated the mechanisms underlying prostaglandin inhibition of histamine-stimulated parietal cell function. Enzyme-dispersed canine parietal cells were enriched by elutriation. The accumulation of the weak base [14C]aminopyrine was used as an index of parietal cell function and cyclic adenosine monophosphate content was measured by radioimmunoassay. Step density gradients of the elutriator-enriched parietal cell fractions indicated that parietal cells accounted for the histamine stimulation of cyclic adenosine monophosphate production and inhibition by the prostaglandin E analogue Enprostil. Pertussis toxin adenosine diphosphate-ribosylates a subunit with a molecular weight of 41,000, thereby inactivating the inhibitory guanine nucleotide-binding protein of adenylate cyclase. Pertussis toxin treatment of parietal cells in overnight suspension culture was used to determine if inhibitory guanosine triphosphate-binding protein mediated prostanoid inhibition. In control cultured cells, prostaglandin E2 and Enprostil markedly inhibited forskolin- and histamine-stimulated aminopyrine accumulation. In parietal cells treated with pertussis toxin (300 ng/ml) for 18 h, stimulation of parietal cell function by histamine, isobutylmethylxanthine, and forskolin was unaltered compared with control cells, whereas prostaglandin E2 and Enprostil inhibition was markedly reduced. In pertussis toxin-treated cells, histamine-stimulated cyclic adenosine monophosphate generation was unaltered, whereas Enprostil inhibition of histamine-stimulated cyclic adenosine monophosphate production was markedly reduced. Pertussis toxin treatment of membranes from control, but not from pertussis toxin-treated, cells induced the [32P]adenosine diphosphate-ribosylation of a membrane protein with a molecular weight of 41,000, presumably the alpha-subunit of inhibitory guanosine triphosphate-binding protein. We conclude that prostanoids inhibit parietal cell function by receptor-mediated interaction with the inhibitory guanine nucleotide-binding protein of adenylate cyclase.

Adenosine Diphosphate Ribose↗
PubMed1988

Hepatic micrometastases in the rat: ferrite-enhanced MR imaging.

A rat tumor model was used to evaluate the ability of ferrite-enhanced magnetic resonance (MR) imaging to demonstrate hepatic metastases smaller than 1 cm. Twenty-eight rat livers were inoculated with 5 X 10(5) mammary carcinoma cells and imaged with a 0.6-T MR system. Non-enhanced and ferrite-enhanced images were analyzed and correlated with autopsy findings for each rat. Lesion detection rates correlated closely with cancer-to-liver contrast-to-noise ratios. Ferrite-enhanced MR imaging demonstrated significantly more lesions than non-enhanced imaging (P less than .05) and decreased the threshold size for lesion detectability (less than 2 mm). Ferrite also enabled more accurate measurements of the lesions (r = .96).

Animals↗
PubMed1988

Use of a multinational survey to provide clinical guidelines for upper gastrointestinal bleeding in developing countries.

The OMGE multinational survey of patients with upper gastrointestinal bleeding demonstrated that it was possible to predict patient outcome, using a computer and a database of information from many centres. It remained to be seen whether this database could be used in specific remote areas of the world. To answer this question, two areas have been studied, Sikkim and China. In Sikkim, when the computer-aided prognostic system was used, 69% of patients put into a high-risk group for rebleeding actually did so; and 54% died. By contrast, only 2% of patients placed into a low-risk group for rebleeding did so. As there is little computer technology in Sikkim, a simplified scoring system was developed which gave the same predictive accuracy as the computer system. In China there was a slightly lower accuracy with both systems. Hence a new database and scoring system were created, using only information from Chinese patients. This database improved the results. From the studies it is suggested that these types of systems can be of value to patients in remote areas by targeting patients at high risk rebleeding or dying, so that the scarce resources available can be best used.

China↗