Biomedical subjects

M D Mitchell

Publications and source records attributed to M D Mitchell.

At least 181 records · Page 10Linked to original sources

PubMed1989

Amniotic fluid arachidonate lipoxygenase metabolites in preterm labor.

This study was conducted to determine if preterm labor with intact membranes is associated with changes in the amniotic fluid concentrations of arachidonate lipoxygenase metabolites. Amniotic fluid was obtained by transabdominal amniocentesis from 68 women with preterm labor. The patients were classified into three groups according to their response to tocolysis and their amniotic fluid culture results: Group 1 - women with a negative amniotic fluid culture who responded to tocolysis (n = 32); Group 2 - women with a negative culture, but who failed to respond to tocolysis (n = 22); and Group 3 - women with intraamniotic infection (n = 14). The following arachidonate lipoxygenase products were measured by radioimmunoassay: leukotriene B4 (LTB4); leukotriene C4 (LTC4); 12-hydroxyeicosatetraenoic acid (12-HETE); and 15-hydroxyeicosatetraenoic acid (15-HETE). The median concentrations of LTB4 were significantly different among the three study groups (26 pg/ml, 67 pg/ml and 885 pg/ml, respectively, p greater than 0.05). Amniotic fluid concentrations of 12-HETE and LTC4 did not vary among the three study groups. On the other hand, a significant difference in the distribution of amniotic fluid concentrations of 15-HETE was noted only between women with intraamniotic infection (Group 3) and women responding to tocolysis (Group 1). These results indicate that the arachidonate lipoxygenase pathway is activated during the course of preterm labor. Selective changes in the concentrations of the assayed metabolites were noted. Amniotic fluid LTB4 concentrations may be a marker for the patient with preterm labor who is unresponsive to tocolysis.

Amniocentesis↗

PubMed1989

Prostaglandin production by cultured cynomolgus monkey trabecular meshwork cells.

Monkey trabecular meshwork (MTM) cells synthesize a variety of prostaglandins, including large amounts of prostaglandin E2 (PGE2) and smaller amounts of 6-keto-PGF1 alpha and PGF2 alpha. The predominance of PGE2 production by the MTM cells is similar to that observed in human trabecular meshwork cells. In contrast, the relative amounts of 6-keto-PGF1 alpha and PGF2 alpha were reversed compared with the human cells. The MTM cells produced increased amounts of PGE2 in response to treatment with bradykinin, platelet activating factor, and A-23187. Dexamethasone caused a dose-dependent inhibition of PGE2 production with 50% inhibition by 10(-8) M, although this response was variable.

6-Ketoprostaglandin F1 alpha↗

PubMed1989

Bacterial endotoxin and tumor necrosis factor stimulate prostaglandin production by human decidua.

The purpose of these studies was to determine the effect of bacterial endotoxin and tumor necrosis factor (TNF) on prostaglandin (PG) secretion by human decidua. Decidual explants were established from women undergoing elective cesarean sections before the onset of labor. Escherichia Coli endotoxin and purified human recombinant TNF (rh TNF) were incubated with decidual explants. PGF2 alpha and PGE2 biosynthesis was measured by radioimmunoassay. A significant increase in the release of all PGs into the media occurred in response to LPS and TNF. In the setting of an extraamniotic infection, bacterial and host secretory products (TNF) could trigger the onset of labor, activating the decidua to produce PGs.

Decidua↗

PubMed1989

Amniotic fluid concentration of 5-hydroxyeicosatetraenoic acid is increased in human parturition at term.

5-hydroxyeicosatetraenoic acid (5-HETE) is an arachidonate lipoxygenase product capable of stimulating uterine contractility in a dose-dependent manner in vitro. The purpose of this study was to determine if spontaneous human labor at term is associated with changes in the concentration of this metabolite in amniotic fluid. Fluid was retrieved from 36 women not in labor and from 30 women in active labor at term. 5-HETE was determined by radioimmunoassay. The median amniotic fluid concentration of 5-HETE of women in labor was significantly greater than that of women not in labor (3538 pg/ml vs. 1977 pg/ml, respectively; p = 0.05). This observation is consistent with activation of the lipoxygenase pathway of arachidonic acid metabolism during spontaneous human parturition at term.

Amniotic Fluid↗

PubMed1989

Effect of food withdrawal on arterial blood glucose and plasma 13,14-dihydro-15-keto-prostaglandin F2 alpha concentrations and nocturnal myometrial electromyographic activity in the pregnant rhesus monkey in the last third of gestation: a model for preterm labor?

Pregnant rhesus monkeys were studied between 109 and 149 days of gestation. Food withdrawal for 48 hours (with free access to water) was accompanied by a decrease in maternal whole blood glucose concentration and an increased maternal arterial plasma 13,14-dihydro-15-keto-prostaglandin F2 alpha concentration. On successive nights of the 48-hour period of food withdrawal, there was an increase in the frequency of myometrial contractions as recorded by uterine electromyogram. In the period after food was returned, blood glucose, arterial 13,14-dihydro-15-keto-prostaglandin F2 alpha concentration, and contraction frequency returned to baseline. Because food withdrawal results in the appearance of the nocturnal contraction pattern seen at term, we suggest that this experimental paradigm may be used as a model for preterm labor.

Animals↗

PubMed1989

The osteoblast-like differentiated phenotype of a variant of MG-63 osteosarcoma cell line correlated with altered adhesive properties.

A cell line, called MG-63.3A, was selected for its resistance to detachment from cell culture by a synthetic peptide containing the fibronectin cell-attachment sequence, Arg-Gly-Asp-Ser. The mechanism of this resistance is probably the 6-fold overproduction of the cell surface fibronectin receptor in MG-63.3A cells (Dedhar et al, J. Cell. Biol. 105, 1175-1182, (1987]. Compared to the parental, tumorigenic MG-63 cells, the non-tumorigenic MG-63.3A cells display strikingly different properties. These include an altered morphology, a slower proliferation rate, ability to form a calcified matrix in vitro, increased synthesis of type I collagen and expression of bone type alkaline phosphatase activity. Studies with purified growth factors indicate that the MG-63 and MG-63.3A cell lines respond to differentially to growth factors; the growth of MG-63 cells if stimulated by PDGF and GM-CSF and inhibited IL-1 beta, whereas the growth of MG-63.3A is unaffected by GM-CSF and IL-1 beta but is stimulated by PDGF and estradiol. We conclude from these data that the MG-63.3A cells may represent a more differentiated cell type with osteoblast-like properties. Studies are currently underway to further characterize, by electron microscopy, the calcified matrix formation by MG-63.3A cells.

Alkaline Phosphatase↗

PubMed1989

Eicosanoid production and glucocorticoid regulatory mechanisms in cultured human trabecular meshwork cells.

The techniques we developed to propagate HTM cells in serial cell culture have provided an opportunity to investigate the spectrum of endogenous PGs and other eicosanoids that are produced by these cells. PGE2 and PGF2 alpha were the major cyclooxygenase products detected by both radioimmunoassay and thin-layer chromatography. A small amount of 6-keto PGF1 alpha was also detected, indicating that these cells are able to produce prostacyclin. The observation of a substantial increase in the proportion of PGF2 alpha relative to PGE2 at later time periods after a media change suggests a metabolic conversion of PGE2 to PGF2 alpha by these cells. Bradykinin, thrombin, platelet activating factor, and serum were found to be effective stimulators of PG production by HTM cells, whereas calcium ionophore produced only a minor effect. Using high pressure liquid chromatography, elution profiles of radiolabeled metabolites of AA suggested the presence of certain lipoxygenase products, including LTB4, 12-HETE, 15-HETE, and a small amount of 5-HETE in HTM cells. The formation of these products was inhibited by both DEX and BW 755c, reinforcing the view that metabolic conversions of AA through the lipoxygenase pathway were possible in the trabecular meshwork. We also examined the effects of glucocorticoids on specific protein synthesis in the HTM cells, using 35S-methionine labeling and SDS-PAGE techniques. Short-term (1 day) DEX treatment revealed a major induction of a protein band at approximately 30 kDa. Longer treatments (1 to 3 weeks) resulted in major inductions at approximately 55 kDa inside the cells, with the presence of secreted forms (probably glycoproteins) between 55 and 72 kDa. The short-term DEX effect on protein synthesis a phospholipase inhibitor regulating eicosanoid production within the HTM. The longer-term induction may, on the other hand, be related more directly to the development of steroid glaucoma, based on our findings that the inductions of these proteins correlate with the observed time course and dose-dependence topical glucocorticoid effects on IOP. Continued in vitro and in vivo evaluations of the eicosanoid pathways in cultured HTM cells obtained from normal and glaucomatous human eyes may help to delineate their relationship to IOP regulation and the pathogenesis and treatment of glaucoma. Glucocorticoid-induced proteins may be key participants in the regulation of phospholipase activity and hence may represent a major control mechanism of the AA cascade.(ABSTRACT TRUNCATED AT 400 WORDS)

Cells, Cultured↗

PubMed1988

Phorbol ester-induced stimulation of prostaglandin biosynthesis in human amnion cells.

Both phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (10(-8)-10(-6) M) induced concentration-dependent increases in prostaglandin E2 (PGE2) production by human amnion cells, with maximum stimulations of 10.8-fold and 5.9-fold, respectively. 4 alpha-Phorbol 12,13-didecanoate, an inactive phorbol ester analogue, had little or no effect on PGE2 production by amnion cells. PMA and phorbol 12,13-dibutyrate (10(-7) M) induced a maximal increase in the rate of PGE2 biosynthesis within 15 min of treatment. These results suggest that there is an active protein kinase C present in amnion cells that is linked to arachidonic acid release and/or metabolism.

Amnion↗

PubMed1988

Paradoxical stimulation of both lipocortin and prostaglandin production in human amnion cells by dexamethasone.

Glucocorticoids inhibit prostaglandin biosynthesis by inducing the formation of lipocortins. In human amnion cells dexamethasone elicited a concentration-dependent increase in prostaglandin production and raised intracellular lipocortin 1 concentrations. Dexamethasone could also potentiate the epidermal growth factor (EGF)-induced stimulation of prostaglandin production. EGF alone or in combination with dexamethasone increased lipocortin 1 formation in amnion cells. Human amnion cells may provide a unique insight into interactions between glucocorticoids, lipocortin and eicosanoid biosynthesis.

Amnion↗

PubMed1988

Characterization of prostaglandin production in amnion-derived WISH cells.

This study was undertaken to characterize prostaglandin production and its regulation in the human amnion-derived WISH cell line. Epidermal growth factor, tumor growth factor-alpha, tumor growth factor-beta, human interleukin-1, tumor necrosis factor, phorbol 12-myristate 13-acetate, phorbol 12,13-dibutyrate, 4 alpha-phorbol 12,13 didecanoate, and dexamethasone were tested for their ability to modulate prostaglandin production in WISH cells. Quantitatively, the major prostaglandin produced in WISH cells was prostaglandin E2. Treatment with epidermal growth factor, tumor growth factor-alpha, tumor necrosis factor, interleukin-1, phorbol 12,13-dibutyrate, and phorbol 12-myristate 13-acetate resulted in a concentration-dependent stimulation of WISH cell prostaglandin E2 production; tumor growth factor-beta and the inactive phorbol ester analog 4 alpha-phorbol 12,13 didecanoate had no effect. Dexamethasone treatment resulted in concentration-dependent inhibition of prostaglandin E2 production by WISH cells. WISH cells responded in a qualitatively similar manner to that previously observed in primary cultures of human amnion with the exception of the response to dexamethasone. On the basis of the findings of this investigation, we suggest that WISH cells may be a useful model for studying some but not all aspects of the regulation of arachidonic acid release and prostaglandin E2 formation in amnion. WISH cells may also be used to evaluate the mechanisms that link regulation of immune function and arachidonic acid metabolism.

Adjuvants, Immunologic↗

PubMed1988

Amniotic fluid 5-hydroxyeicosatetraenoic acid in preterm labor.

5-Hydroxyeicosatetraenoic acid (5-HETE) is an arachidonate lipoxygenase product capable of stimulating human uterine contractility in a dose-dependent manner in vitro. The purpose of this study was to determine if preterm labor is associated with changes in the concentration of this metabolite in amniotic fluid. Amniotic fluid was obtained by transabdominal amniocentesis from three groups of women with preterm labor: group 1 - women without intraamniotic infection who responded to tocolysis (n = 32); group 2 - women without intraamniotic infection who failed to respond to tocolysis (n = 22); and group 3 - women with intraamniotic infection (n = 14). 5-HETE was determined by radioimmunoassay. The median amniotic fluid concentration of 5-HETE in women who responded to tocolysis (median = 1412 pg/ml; range: 111-3547) was significantly lower than in women who delivered despite tocolysis (median = 2052 pg/ml; range: 136-7774) and women with intraamniotic infection (median = 1876 pg/ml; range: 543-7033) [p less than 0.05]). No difference in amniotic fluid concentrations' of 5-HETE were found between women in groups 2 and 3 (p greater than 0.05).

Adult↗

PubMed1988

Trauma peptide-mediated prostaglandin E2 biosynthesis: a potential mechanism for trauma-induced immunosuppression.

In vitro exposure of peripheral-blood-adherent mononuclear cells or amnion cells to nanomolar quantities of a trauma-associated immunosuppressive peptide resulted in an increased biosynthesis of prostaglandin E2 (PGE2). Trauma peptide enhanced prostaglandin E2 biosynthesis by as much as 425% compared to buffer controls. The addition of trauma peptide to mixed lymphocyte cultures significantly inhibited [3H]thymidine incorporation by human peripheral blood lymphocytes. Addition of indomethacin (an inhibitor of prostaglandin biosynthesis) to mixed lymphocyte cultures did not significantly abrogate the immunosuppressive activity of the peptide. These results indicate that suppression of T lymphocyte blastogenesis by trauma peptide is probably mediated by at least two mechanisms: (1) by increased PGE2 biosynthesis, induced by trauma peptide, and (2) through a non-cyclooxygenase-mediated pathway.

Dinoprostone↗

PubMed1988

Plasma prostaglandins in lung cancer.

Plasma levels of three stable prostaglandin (PG) metabolites were measured in 29 patients with lung cancer. The mean level of 6-keto-PGF1 alpha, the hydrolysis product of prostacyclin, was significantly elevated in cancer patients compared to a control group with non-malignant respiratory disorders, although an overlap in values between the groups was seen. Levels correlated inversely with survival and showed a significant fall in 14 patients with tumour regression. The mean level of 11-deoxy-3,14-dihydro-15-keto-11,16-cyclo-prostaglandin E2 was also significantly elevated in cancer patients, but did not correlate with tumour response. 13,14-Dihydro-15-keto prostaglandin F2 alpha levels did not differ in lung cancer patients and controls. Contrary to previous reports we could not support a role for the metabolites of PGE2 and PGF2 alpha as tumour markers in lung cancer but plasma 6-keto-PGF1 alpha should be further evaluated in this regard.

6-Ketoprostaglandin F1 alpha↗

PubMed1988

Amniotic fluid prostaglandin E2 in preterm labor.

These studies were designed to determine amniotic fluid concentrations of prostaglandin E2 (PGE) in women with preterm labor. Amniotic fluid was retrieved by transabdominal amniocentesis from 68 women with preterm labor (less than 37 weeks). Patients were divided into three groups according to the response to tocolysis and the presence or absence of an intraamniotic infection. Amniotic fluid concentrations of PGE2 were significantly greater in women with preterm labor and intraamniotic infection than in women without infection. Patients unresponsive to tocolysis without intraamniotic infection had a significantly greater concentration of PGE2 in amniotic fluid than those responsive to tocolysis.

Adult↗

PubMed1988

Increased amniotic fluid leukotriene C4 concentration in term human parturition.

The purpose of this study was to determine whether parturition is associated with changes in the amniotic fluid concentration of leukotriene C4, an arachidonate lipoxygenase metabolite. Amniotic fluid was collected from 36 women not in labor and from 30 women in active labor with cervical dilation of greater than or equal to 6 cm. The concentration of leukotriene C4 was determined by radioimmunoassay. The median amniotic fluid concentration of leukotriene C4 was greater in laboring women than in nonlaboring women: 121 pg/ml (range, 52 to 261 pg/ml) versus 73.5 pg/ml (range, 6 to 249 pg/ml), respectively (p = 0.0008). These data are consistent with activation of the lipoxygenase pathway during spontaneous parturition at term.

Amniotic Fluid↗

PubMed1988

Cyclooxygenase products formed by primary cultures of cells from human chorion laeve: influence of steroids.

Cells were isolated from human chorion laeve obtained at term (38-40 weeks gestation) by elective caesarean section and were maintained in primary culture for 1 week in defined media supplemented with 10% fetal calf serum. The production of various cyclooxygenase products by the cultures was examined. Little or no prostaglandin (PG) F2 alpha, 6-keto-PGF1 alpha, thromboxane B2, or 13,14-dihydro-15-keto-PGF2 alpha was found. In contrast, the cells produced PGE2 which was low on day 0, increased during culture to a maximum on day 1 or 2, then declined to low levels. When cells were grown in the presence of media containing cortisol, dexamethasone, progesterone, and estradiol (at 10(-7) or 10(-9) M), the glucocorticoids (at 10(-7) and 10(-9) M), but not estrogen or progesterone, markedly inhibited the increase in PGE2 output. There was no difference in the protein content and thymidine incorporation of cells grown in the presence of glucocorticoids when compared with controls. This inhibitory effect was not sensitive to cycloheximide (1 microgram/mL) indicating protein synthesis may not be involved in the process. These studies indicate that PGE2 is the major prostaglandin formed by primary cultures of chorion laeve and that prostaglandin metabolism in the chorion is sensitive to glucocorticoid inhibition.

Cells, Cultured↗

PubMed1988

Pulmonary intravascular macrophages and hemodynamic effects of liposomes in sheep.

We studied the effects of liposomes on the pulmonary circulation of sheep and found a close correlation between liposome retention in the lung and the intravascular macrophages. A test dose of liposomes (5.5 mumol of total lipids) injected intravenously transiently increased pulmonary arterial pressure from 24 +/- 2 to 55 +/- 16 (SD) cmH2O. The pulmonary arterial pressure responses were dose dependent and reproducible. The rise in pulmonary arterial pressure was blocked completely by indomethacin and 75% by a thromboxane synthase inhibitor. Systemic arterial thromboxane B2 concentration increased from a base-line level of less than 50 pg/ml to 250 +/- 130 pg/ml at the peak of the pressor response. Larger doses of liposomes (220 mumol of total lipids) infused intravenously over 1 h increased pulmonary arterial pressure maximally within the first 15 min. Lymph flow increased and lymph protein concentration decreased, suggesting venoconstriction. Over half (62.4 +/- 15.7%) of 111In-labeled liposomes remained in the lung after 2 h. Fluorescence and transmission electron microscopy showed that greater than 90% of the liposomes were associated with mononuclear cells in the lumen of the alveolar wall microvessels. We conclude that liposomes affect pulmonary arterial pressure transiently by a mechanism involving the arachidonate cascade, principally thromboxane. Our observations suggest that a population of pulmonary intravascular macrophages is likely to be the source of the thromboxane and the pulmonary hemodynamic and lymph dynamic changes that occur in a dose-dependent fashion, although interactions between liposomes, leukocytes, or endothelial cells, in addition to the macrophages, have not been completely ruled out. We believe this is the first demonstration that pulmonary intravascular macrophages may be the source of the arachidonate metabolites rather than endothelial cells, neutrophils, or perivascular interstitial cells.

Animals↗

PubMed1988

Prostaglandin concentrations in cerebrospinal fluid of rabbits under normal and ischemic conditions.

Clinical studies have demonstrated elevated levels of both arachidonic acid and prostaglandins in the cerebrospinal fluid of humans after ischemic stroke and subarachnoid hemorrhage. Such increases in free fatty acid, arachidonic acid, and prostaglandin concentrations suggest excessive production and accumulation of these substances in the ischemic brain. We used a rabbit model of ischemic infarction to examine the relation between controlled central nervous system ischemia and cerebrospinal fluid prostaglandin levels. We found that following stroke PGF2 alpha and not PGD2 was the predominant prostaglandin present in the cerebrospinal fluid. PGF2 alpha also underwent the largest percent increase over control prostaglandin concentrations. This is similar to human and dog cerebrospinal fluid studies, which demonstrate PGF2 alpha as the predominant prostaglandin following ischemic injury. The lack of PGD2 elevation under ischemic conditions may suggest that the rabbit model is more like stroke in humans than the rat or gerbil models. Our preliminary work demonstrates that it is practical to study postischemic prostaglandin changes in cerebrospinal fluid rather than in brain tissue in a rabbit model of central nervous system ischemia.

Animals↗