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Biomedical subjects

S M Chen

Publications and source records attributed to S M Chen.

At least 145 records · Page 8Linked to original sources
PubMed1984

Pathogenesis of gastric ulceration produced by acetazolamide in rats.

The present experiment demonstrated that relatively high doses of acetazolamide (100 and 200 mg/kg s.c.) induced severe gastric hemorrhagic ulceration in rats. This ulceration was aggravated by oral administration of HC1, but was inhibited by NaHCO3. Further, the severity of ulceration was also decreased by pretreatment with methysergide, chlorpheniramine, or cimetidine. These protective effects were affirmed by an increase in serotonin and histamine released from the stomach after acetazolamide treatment. Acetazolamide injection also increased the protein level, but reduced the sialic acid content in the gastric secretion, indicating that the gastric mucosal barrier may have been damaged. Prostaglandin E2 content of the gastric mucosa was not affected by the drug; however, carbonic anhydrase activity was markedly reduced in a dose-dependent manner. Thus, it is suggested that the ulceration induced by acetazolamide is mainly due to the inhibition of carbonic anhydrase activity and mucus secretion. The increases in serotonin and histamine released may also have been contributing factors for gastric ulcer formation.

Acetazolamide↗
PubMed1983

The lack of effects of somatostatin on gastric responses induced by electrical vagal stimulation.

The effects of somatostatin on ulcer formation, gastric acid secretion and histamine release were assessed during vagus nerve stimulation in rats. Direct electrical vagal stimulation significantly increased histamine release and acid output in gastric secretion but decreased mast cell counts in gastric glandular mucosa. Hemorrhagic ulceration on the gastric glandular mucosa was also observed. Somatostatin pretreatment (10 micrograms/kg) did not inhibit gastric ulcer formation, gastric acid secretion or histamine release induced by vagal stimulation. Cimetidine (an H2 blocker) pretreatment, however, significantly decreased gastric acid secretion as well as ulcer formation. The present study indicates the direct vagal stimulation increases gastric acid secretion and ulcer formation. These effects are partially histamine dependent. Somatostatin did not inhibit histamine release induced by vagal stimulation and reflects the inability of the drug to prevent ulcer formation and gastric output under these conditions in rats. However, the inhibition of basal gastric acid secretion produced by somatostatin might be useful clinically in humans.

Animals↗
PubMed1981

In vivo and in vitro studies on the mechanism of cardiovascular effects of Wu-Chu-Yu (Evodiae fructus).

The effects of the Chinese herb Wu-Chu-Yu (Evodiae fructus) on the cardiovascular function were assessed in anesthetized cats, conscious rats, and isolated preparations of rat aortic strip and auricle. In anesthetized cats, intravenous administration of alcohol-water crude extracts of Wu-Chu-Yu (0.03-0.24 g/kg) produced a dose-dependent hypertension and an increased contractile force of nictitating membrane which lasted for more than 5 min in higher doses. Phentolamine, but not tetraethylammonium antagonized hypertension and the increased contractile force of nictitating membrane induced by Wu-Chu-Yu. In conscious rats, hypertension was also observed by intraperitoneal administration of Wu-Chu-Yu (6 g/kg). Bilateral nephrectomy, administration of phentolamine or propranolol, all significantly decreased the hypertensive effect of Wu-Chu-Yu. Pretreatment with reserpine 24 hours in advance did not change the pressor effect of the crude extract. In aortic strip preparations, Wu-Chu-Yu caused the increase of contractile force, and the dose-response curve was parallel shift to the right in the presence of phentolamine. In auricle preparations, Wu-Chu-Yu produced positive inotropic and positive chronotropic effects, and the presence of propranolol changed the slope of Wu-Chu-Yu's dose-inotropic effect curve and reversed the chronotropic effect from positive to negative. Both in vivo and in vitro results suggested that alpha and beta adrenoceptors were directly involved in the cardiovascular effects of Wu-Chu-Yu.

Animals↗
PubMed1981

Protective effects of Carica papaya Linn on the exogenous gastric ulcer in rats.

The effects of Carica papaya Linn on exogenous ulcer and histamine-induced acid secretion were studied in rats. The latex of the unripened fruit of C. papaya was effective in protecting the exogenous ulcer. It significantly lessened the acid secretion induced by intravenous infusion of histamine in chronic gastric fistulated rats. Crystalline papain was also effective in protecting the exogenous ulcer and in decreasing the histamine-induced acid secretion in rats. The conclusion is that papain is the active principle in C. papaya that exerts the ulcer-protective effect.

Animals↗
PubMed1980

Mitochondrial DNA replication does not involve DNA polymerase alpha.

Aphidicolin, a known inhibitor of DNA polymerase alpha, is a potent inhibitor of nuclear DNA synthesis in HeLa cells but has no effect on the replication of mitochondrial DNA. Parallel experiments with mitochondria incubated in vitro also show no inhibition of DNA synthesis by aphidicolin; however, DNA synthesis in these isolated mitochondria is completely blocked by dideoxycytidine triphosphate, which inhibits DNA polymerase gamma but not the alpha polymerase. The replication of mitochondrial DNA therefore requires only one DNA polymerase of the gamma type.

Aphidicolin↗
PubMed1979

Prostaglandins and congeners XXIII (1). Synthesis of 15-deoxy-16-hydroxy-16-methylprostanglandins. The importance of the C13--C14 trans double bond for bronchodilator activity.

The synthesis and bronchodilator activity in the guinea pig of several 15-deoxy-16-hydroxy-16-methylprostaglandin analogs is described. The E2 (VIa) and E1 (VIb) analogs are potent bronchodilators comparable in activity to the natrual prostaglandins, but possessing a longer duration of effect. Replacement of the C13--C14 trans double bond by a cis double bond or an ethylene linkage causes a substantial diminishment of this activity.

Animals↗
PubMed1978

Evidence that spo0A mutations are recessive in spo0A-/spo0A+ merodiploid strains of Bacillus subtilis.

The spo0A locus contains two types of closely linked mutations that block sporulation at stage 0: spo0A mutations (the most pleiotropic of the stage 0 markers) and spo0C mutations. It was previously thought that spo0A mutations were dominant in merodiploids of Bacillus subtilis, whereas spo0C mutations were recessive. We have shown that spo0A mutations were recessive when spo0A-/spo0A+ merodiploids were made in the genetic backgrounds of strains that were resistant to antibiotic produced by the wild-type strain. Reinvestigation of cultures of spo0A-/spo0A+ merodiploids constructed in the antibiotic-sensitive spo0A strain showed that they contained the spo0A allele at a low frequency, and they produced very few haploid Spo- segregants. These facts indicated that the cultures contained mostly homogenotic (spo0A+/spo0A+) cells. The reason for the poor survival of the spo0A-/spo0A+ merodiploids in the genetic background of the antibiotic-sensitive strain was not clear, but several possible explanations were given. It may have been related to the diploid state of other genes in the same merodiploid cells. The previous indication that spo0A mutations were dominant seems to have been based on the properties of a rare class of Spo- segregants that were probably selected in the presence of antibiotic.

Anti-Bacterial Agents↗
PubMed1977

Control of anthocyanin synthesis by the C locus in maize.

Alleles at the C locus in maize include C, one of the complementary genes required for anthocyanin pigmentation in the aleurone tissue of the mature kernel; C-I, dominant inhibitor of pigmentation; and c, recessive colorless. The recessive colorless alleles can be differentiated into two distinct forms: c-p (p for positive), conditional colored, develops pigment in the light during germination; c-n (n for negative), colorless, fails to develop pigment at any time. Four-point linkage data support the differentiation of c-p (in the alleles derived from either W22 or K55 inbreds) from c-n. Light and germination conditions are both required for anthocyanin synthesis in c-p tissue, but light "induction" and germination "induction" are two separable events inasmuch as the light stimulus can be stored. The ratio between the two major pigments, cyanidin and pelargonidin, is lowered in c-p tissue relative to that in dominant colored (C) tissue for the W22 allele and background but not for the K55 allele and background. Segregation tests reveal that the difference in the cyanidin-to-pelargonidin ratio in the C and the c-p tissue of W22 background is associated with the C locus. Several properties of the C locus, including anomalous allelic functions, stage- and properties of the C locus, including anomalous allelic functions, stage- and condition-dependent anthocyanin synthesis controlled by its multiple allelic series, and tissue-specific function, suggest that C may be a regulatory locus in the control of anthocyanin synthesis in aleurone tissue.

Alleles↗