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Biomedical subjects

X M Sun

Publications and source records attributed to X M Sun.

85 records · Page 5Linked to original sources
PubMed1990

Hypoxia causes ischemic bowel necrosis in rats: the role of platelet-activating factor (PAF-acether).

We have previously shown that injection of platelet-activating factor causes necrotizing enterocolitis in the rat and that platelet-activating factor is an endogenous mediator in lipopolysaccharide-induced bowel necrosis. Because hypoxia is a known predisposing factor for neonatal necrotizing enterocolitis, we investigated the effect of hypoxia on platelet-activating factor formation and intestinal necrosis. Young male Sprague-Dawley rats were made severely hypoxic by placing them in a 100% N2 chamber for 2 minutes; moderate hypoxia was accomplished using 10% O2 for 15 or 30 minutes. To evaluate the role of platelet-activating factor on intestinal perfusion and injury, two platelet-activating factor antagonists, SRI 63-441 and WEB 2086, were injected 10 minutes before the hypoxic exposure. We found that plasma platelet-activating factor levels were significantly elevated after 2 minutes of severe hypoxia (13.8 +/- 2.9 ng/mL vs. control 2.1 +/- 0.8 ng/mL) and after 30 minutes of moderate hypoxia (41.1 +/- 11.7 ng/mL). This increase in platelet-activating factor level was not caused by decreased degradation, because neither plasma nor intestinal platelet-activating factor acetylhydrolase was decreased in the hypoxic rats. (Intestinal acetylhydrolase activity was actually increased). Intestinal perfusion was markedly decreased at 30 minutes in hypoxic animals. In contrast, all platelet-activating factor antagonist-treated animals had normal intestinal perfusion. Histological examination of affected bowel from hypoxic animals showed early intestinal necrosis which was completely prevented by pretreatment with SRI 63-441 and WEB 2086. Because 30 minutes of hypoxia also resulted in metabolic acidosis, we further investigated if acidosis alone could induce platelet-activating factor release and bowel injury. We found that acidosis alone resulted in moderate increase of plasma platelet-activating factor but did not produce bowel injury. We conclude that platelet-activating factor plays a central role in mediating hypoxia-induced intestinal necrosis. Acidosis may enhance the effect of hypoxia on platelet-activating factor production.

Animals↗
PubMed1990

Role of platelet activating factor and tumor necrosis factor-alpha in neonatal necrotizing enterocolitis.

Because previous investigations have suggested that platelet activating factor and tumor necrosis factor-alpha (TNF-alpha) are important mediators of experimental necrotizing enterocolitis in the rat, we measured platelet activating factor, acetylhydrolase (the platelet activating factor breakdown enzyme), and TNF-alpha in the plasma of 12 human neonates with necrotizing enterocolitis and eight age-matched control subjects with similar gestational ages, postnatal ages, and weights. Almost all patients with necrotizing enterocolitis had elevated plasma platelet activating factor values (18.1 +/- 3.6 ng/ml vs. 3.1 +/- 0.9 ng/ml in control subjects, p less than 0.01). Plasma acetylhydrolase activity was lower in patients than in control subjects (10.6 +/- 0.7 nmol/ml/min vs 23.0 +/- 1.4 nmol/ml/min, p less than 0.01). Plasma TNF-alpha concentration was significantly elevated in patients with necrotizing enterocolitis (136 +/- 75 U/ml vs 1.5 +/- 0.8 U/ml, p less than 0.05), although the individual variation was high. There was no correlation between individual TNF-alpha and platelet activating factor levels. We conclude that platelet activating factor and TNF-alpha are elevated in patients with necrotizing enterocolitis and that suppressed platelet activating factor degradation contributes to the increased platelet activating factor levels; platelet activating factor and TNF-alpha may contribute to the pathophysiology of necrotizing enterocolitis.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1990

Circulating plasma platelet activating factor in persistent pulmonary hypertension of the newborn.

Platelet activating factor (PAF) is an endogenous phospholipid mediator that causes pulmonary hypertension and thrombocytopenia in experimental animal models. To investigate circulating PAF in persistent pulmonary hypertension of the newborn (PPHN), we studied PAF and its degradative enzyme, acetylhydrolase. Thirteen neonates with PPHN, diagnosed by routine clinical methods including echocardiography, were compared to six age-matched control patients with respiratory distress. Overall, plasma PAF levels were elevated in patients with PPHN compared to control patients (20.1 +/- 3.9 versus 1.6 +/- 0.7 ng/ml, p less than 0.01). In addition, plasma PAF concentrations in patients with PPHN correlated with the severity of disease as defined by the delta AaPO2 (r = 0.65, p = 0.015). In three patients with elevated PAF levels, as the clinical status improved, the plasma PAF values decreased. Acetylhydrolase activity was similar in both groups (3.96 +/- 0.90 versus 3.78 +/- 1.44 nmol/ml/min, p = NS). We conclude that PAF production is increased in PPHN and that abnormal production of PAF may be associated with pulmonary hypertension.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1990

Effects of in vivo 'priming' on endotoxin-induced hypotension and tissue injury. The role of PAF and tumor necrosis factor.

Exogenously administered tumor necrosis factor-alpha (TNF) and bacterial endotoxin (LPS) induce shock and tissue injury. Here, the authors studied the effect of endogenous TNF on LPS-induced hypotension and tissue injury and investigated the role of PAF in these responses. Rats were primed with intraperitoneal injection of zymosan 24 hours before, or Bacillus Calmette-Guérin (BCG) 12 to 15 days before intravenous injection of low dose (0.5 mg/kg) LPS. It was found that nonprimed animals showed mild hypotension and moderate leukopenia in response to LPS. In contrast, zymosanprimed rats developed shock and marked leukopenia, and more severe bowel injury than nonprimed rats. The authors then showed that, following LPS injection, zymosan-primed animals had higher TNF and platelet-activating factor (PAF) levels than nonprimed rats. Pretreatment of the animal with PAF antagonist, SRI 63-441, markedly ameliorated the hypotension and tissue injury. Interestingly, BCG-primed rats did not show aggravation of LPS-induced hypotension. Only TNF (but not PAF) level in these animals was increased. Thus, it appears that TNF release alone, without a sufficient increase in PAF, is incapable of causing severe hypotension. However, most of the BCG-primed animals showed tissue injury, which could be prevented by pretreatment with PAF antagonist. The authors discuss the possible mechanisms of this discrepancy between systemic and local responses in BCG-primed animals.

Animals↗
PubMed1990

[Effect of 2-naphthyl-3- (3,4-dimethoxy) phenyl-propenoic acid on the metabolism of arachidonic acid in rabbit platelets].

Washed rabbit platelets were incubated with [14C] arachidonic acid (AA sodium salt) after being exposed to 2-naphthyl-3-(3,4-dimethoxy) phenyl-propenoic acid (NM-PA), indomethacin (Ind) and imidazole (Imi) or control solvent. The metabolites of AA in rabbit platelets were separated with the system of chloroform: methanol: acetic acid: water (90:8:1:0.8) by thin layer chromatography and quantitated by liquid scintillation counter. The metabolism of AA was influenced by NMPA dose-dependently in the range of 0.05-0.5 mmol/L. The formation of thromboxane B2 (TXB2) and 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT), the final metabolites in the pathway of cyclooxygenase-thromboxane synthetase, were decreased from 24 +/- 6.7 to 3.2 +/- 1.6% and 10.3 +/- 2.49 to 4.7 +/- 2.8%, respectively. Meanwhile, 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), the metabolite in the pathway of lipoxygenase, was increased from 11.9 +/- 1.7 to 34 +/- 5.6%. It is suggested that NMPA blocks the pathway of cyclooxygenase-thromboxane synthetase and then changes the direction of arachidonate metabolism in platelets, the activation of platelets is inhibited in this way.

Animals↗
PubMed1989

[Use of amphotericin B-cells to detect inhibitors of cellular cholesterol biosynthesis].

A new method for detecting inhibitors of cellular cholesterol biosynthesis is reported. It was established according to the principle that amphotericin B binds sterols in the membranes of animal cells to form a complex which kills the cells. The method was simple, reliable and easy to handle. Moreover, the cost was low. Using this method, the authors had screened twenty Chinese herbs and found that Salvia miltiorrhiza and its extracts inhibit cellular cholesterol biosynthesis efficiently.

Amphotericin B↗
PubMed1988

Bowel necrosis induced by tumor necrosis factor in rats is mediated by platelet-activating factor.

We have developed a rat model of ischemic bowel necrosis associated with shock by injection of platelet-activating factor (PAF) or a combination of PAF and endotoxin. Recent investigations have shown that tumor necrosis factor (TNF) also induces shock and necrosis of the gastrointestinal tract. The morphological changes of TNF-induced bowel lesions are indistinguishable from those caused by PAF. The mechanism of TNF-induced bowel necrosis is unclear. In the present study, we have shown that (a) TNF caused PAF production in bowel tissue; (b) the effects of TNF and LPS on PAF production in the intestine are additive; (c) TNF and LPS are synergistic in inducing bowel necrosis; and (d) TNF-induced bowel necrosis is due to PAF release and can be prevented by pretreatment with PAF antagonists.

Animals↗
PubMed1987

Determination of artemether in plasma and whole blood using HPLC with flow-through polarographic detection.

An HPLC method with polarographic detection for the trace determination of artemether in plasma and whole blood was developed and applied to pharmacokinetic and clinical pharmacological studies. The method showed high sensitivity and selectivity because of the easy reduction of the peroxide linkage of artemether at the mercury drop electrode. The detection limit was 10 ng and the detector response was linear over the range of 10 ng to 1 microgram artemether injected onto the column. The largest relative standard deviation of 10 replicate measurements of standard solutions (concentrations of 10 ng/mL-1 microgram/mL) was 8%. The recovery from whole blood and plasma of added drug (concentrations of 15-480 ng/mL) was 71-100%.

Animals↗